Geologic Map of the

Huerfano Hill Quadrangle,

Sierra County, New Mexico

By

Colin T. Cikoski and Daniel J. Koning

June 2013

New Mexico Bureau of Geology and Mineral Resources Open-file Digital Geologic Map OF-GM 243

Scale 1:24,000

This work was supported by the U.S. Geological Survey, National Cooperative Geologic

Mapping Program (STATEMAP) under USGS Cooperative Agreement and the

New Mexico Bureau of Geology and Mineral Resources.

New Mexico Bureau of Geology and Mineral Resources

801 Leroy Place, Socorro, New Mexico, 87801-4796

The views and conclusions contained in this document are those of the author and should not be interpreted as necessarily representing the official policies,

either expressed or implied, of the U.S. Government or the State of New Mexico.

1

SYNOPSIS

Situated 15-27 km (9-17 mi) north of Truth or Consequences, NM, the Huerfano

Hill quadrangle exhibits an extensive, high-level, east-sloping surface locally

incised by east- and southeast draining arroyos (Fig. 1). These drainages

generally cut less than 30 m (100 ft) into this surface. Two major canyons include

Monticello Canyon and Willow Springs Draw. Monticello Canyon is the larger of

the two, being 60 m (200 ft) deep and 0.8-1.6 km (0.5 -1.0 mi) wide (Fig. 1).

Alamosa Creek flows through Monticello Canyon, draining the northern

Winston graben and exhibiting a suite of 6 correlated terraces. The

aforementioned high-level surface is called the Cuchillo surface and exhibits an

extensive stage IV, locally stage III, carbonate horizon (McCraw, 2012; McCraw

and Love, 2012; Gile et al., 1966). This petrocalcic soil serves as a protective cap

that inhibits slope retreat of the few deep canyons.

Aside from constructing the cross section, most of our efforts for this project

involved mapping volcanic units in the Sierra Mediano (northwest corner) and

differentiating Holocene-Pleistocene valley bottom and terrace deposits

associated with the east- to southeast-flowing drainages. The Sierra Mediano are

capped by the Vicks Peak Tuff (from the 28.8 Ma caldera explosion associated

with the Nogal caldera; Furlow, 1965; Farkas, 1969; Deal and Rhodes, 1976) that

overlie andesite lava flows. The valley-bottom and terrace deposits range in age

from modern to middle Pleistocene.

The valley-bottom and terrace deposits overlie the older Palomas Formation

(Plio-Pleistocene), a non-tilted unit that extends across the quadrangle and which

2

Figure 1. View looking north across Monticello Canyon towards the southern

San Mateo Mountains. The prominent alluvial fan in the center of the

photograph lies at the mouth of Questa Blanca Canyon, a tributary to Monticello

Canyon. The location of Questa Blanca Canyon approximately coincides with the

north-striking, west-down Willow Draw fault. Note the multiple terraces

preserved on the north slope of Monticello Canyon. The flat surface marked by

arrows is the Cuchillo surface. This surface represents the culmination of Santa

Fe Group deposition at 0.8 ka (McCraw and Love, 2012; Mack et al., 1993; 1998;

Leeder et al., 1996; Seager and Mack, 2003; Mack et al., 2006). The Cuchillo

surface has been displaced ~12 m (40 ft) down-to-the-west by movement along

the Willow Draw fault.

overlies older, tilted, variably cemented, non-differentiated Santa Fe Group

strata. The Palomas Formation is generally a sandy gravel piedmont facies.

Gravelly channel-fills progressively decrease, and clayey-silty sands increase,

laterally in an eastward direction. The axial facies, associated with the ancestral

Rio Grande, are only mapped along the bottom of Alamosa Creek within 900 m

(3000 ft) of the eastern quadrangle boundary.

3

Strata below the Palomas Formation dip eastward, and faults generally strike

north-south and dip westward. The main structure on the quadrangle is the Mud

Springs fault, which experienced at least 3600 m of west-down, stratigraphic

displacement. Another major fault, the Willow Draw fault, is located near the

western border of the quadrangle. The Willow Draw fault has been more active

in the past 780,000 years than the Mud Springs fault, as evidenced by scarp

heights (~6 m vs. ~2 m, respectively), even though the latter has experienced far

more cumulative movement over the past 26 million years. A south-dipping

ramp structure may exist in the subsurface between the mapped north end of the

Mud Springs fault and the northern Willow Draw fault. This ramp is probably

broken by WNW-striking, normal oblique-slip (?) faults whose stratigraphic

displacements are mostly down-to-the-south. Bedrock faults and associated

fractures may act to introduce warm ground water, traveling via deep flow

paths, into pre-Palomas Santa Fe Group strata.

INTRODUCTION

Geographic setting

The Huerfano Hill quadrangle is located 15-27 km (9-17 mi) north of Truth or

Consequences in south-central New Mexico. The climate here is arid. Total

yearly precipitation averages only 25 cm (10 inches) and arrives largely in two

pulses: winter precipitation that is dominated by snow (average of 3 inches) and

summer preciptation characterized by summer monsoonal storms (Western

Regional Climate Center, 2009). The terrain is characterized by an extensive,

high-level, east-sloping, piedmont surface locally incised by east- and southeast

draining arroyos. This surface is called the Cuchillo surface and exhibits an

extensive stage IV, locally stage III, carbonate horizon (McCraw and Love, 2012;

4

McCraw, 2012; Gile et al., 1966). This petrocalcic soil serves as a protective cap

that inhibits slope retreat of the few deep canyons. Plant life on the Cuchillo

surface is dominated by a sparse cover of creosote. More diverse desert plants

are present in the canyon bottoms, including mesquite and desert willow.

Near the northern border of the quadrangle lie two sets of hills. The larger of

these sets is the Sierras Mediano, found 3 km (2 mi) east of the northwest corner

of the quadrangle. The Sierras Mediano rise up to 120 m (400 ft) above the

Cuchillo surface. Three km (2 mi) to the east of the Sierras Mediano lies the

relatively small Huerfano Hill, which stands only 25 m (~80 ft) above the

Cuchillo surface. Both the Sierras Mediano and Huerfano Hill are composed of

volcanic rocks (i.e., the Vicks Peak Tuff underlain, in the Sierras Mediano, by

older andesite).

Drainages generally cut less than 30 m (100 ft) into the Cuchillo surface. Two

major canyons include Monticello Canyon and Willow Springs Draw. Monticello

Canyon is the larger of the two, being 60 m (200 ft) deep and 0.8-1.6 km (0.5 -1.0

mi) wide. Alamosa Creek flows through Monticello Canyon; it drains the

northern Winston graben and exhibits a suite of 6 correlated terraces. Monticello

Canyon is the only inhabited area of the quadrangle, probably because

groundwater is shallower here compared to other places.

Wells

Several wells are plotted on the geologic map. Most of these consist of water

wells that contain useful lithologic well logs. Based on these well logs, depth to

water in the Monticello Canyon wells is generally less than 60 m (200 ft). Three

deep, oil exploratory wells are also plotted on the geologic map. These wells

5

proved useful in this study because their cuttings and geophysical well logs

could be accessed in the Petroleum Records Library at the New Mexico Bureau of

Geology and Mineral Resources. From west to east, these wells include: Gartland

1 Garner, West Elephant Butte Federal No. 1, and Gartland 1 Brister (Table 1).

Table 1. Oil exploratory wells found in the Huerfano Hill quadrangle

Well name (completed drill

date)*

API Owner API Township, Range, Section

Location within

section**

Depth to base of

Palomas Fm

Gartland 1 Garner (12/21/1950)

N/A Thomas J. Gartland

N/A T12S, R5W, sec. 11

660’FSL & 1980’FEL

355 ft

West Elephant Butte Federal No. 1 (12/12/1982)

30-051-20009

Getty Oil 30-051-20009

T12S, R4W, sec. 7

990’FNL & 2310’FEL

525 ft

OWDD: Gartland 1 Brister (9/20/1955) ORIG: Gartland #1 Drew-Matthews (10/3/1951)

30-051-00007

Thomas J. Gartland

30-051-00007

T12S, R4W, sec. 8

2010’FSL & 1988’FEL

522 ft

Notes: Information provided by Annabelle Lopez of the NM Bureau of Geology and Mineral Resources * ORIG: Original well; OWDD: Original well that was drilled deeper at a later date ** FEL: Feet west from east boundary of section; FNL: Feet south from north boundary of section; FSL: Feet north from the south boundary of section.

STRUCTURE

Two large, east-tilted structural basins are found on the Huerfano Hill

quadrangle: the Palomas Basin to the west and the western, shallow part of the

Engle Basin to the east. These basins are separated by the Mud Springs fault,

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which is described in more detail below. The Palomas Basin extends southward

past Truth or Consequences (west of the Mud Springs Hills). Immediately east of

the Mud Springs fault, corresponding with the easternmost, shallow part of the

Engle basin, lies a structural high that continues south to the Mud Springs

Mountains. Basin-fill is relatively thin (less than ~500 m (1650 ft) thick) over this

structural high. Near the northern boundary of the quadrangle, this structural

high extends westward to the western quadrangle boundary and includes the

Sierras Mediano and Huerfano Hill. The structural high is tilted eastward and

overlying basin-fill thickens eastward into the Engle Basin.

Strata on the Huerfano Hill quadrangle dip eastward by various degrees, as is

illustrated in cross section A-A.' Dips of the Palomas Formation (units QTpp

and QTpa) approximately parallel modern stream grade (0.5-0.7°E). Based on

stratigraphic correlations between the W. Elephant Butte Federal No. 1 and the

Gartland 1 Brister oil exploratory wells, locally differentiated intervals within the

pre-Palomas Santa Fe Group (Tsf, described below) dip 1-4° E (apparent dip),

with dips increasing with depth. The basal contact of unit Tsf has an apparent

dip of 5° E. The eastward splaying of dips in unit Tsf indicates that it was

deposited during active tilting of the footwall block of the Mud Springs fault. On

the footwall of the Mud Springs fault, the large discrepancy between the slope of

the Tsf basal contact and dips within bedrock strata indicate prolonged eastward

tilting prior to the erosional development of the Tsf basal contact. Although

some of this pre-Tsf tilting may have occurred during the Laramide orogeny, we

interpret that additional tilting took place during the early to middle phases of

Rio Grande rifting -- mainly because dip magnitudes of the post-Laramide

Turkey Springs Tuff (in the Sierras Mediano and Huerfano Hill) fall between that

of Tsf on the footwall of the Mud Springs fault (1-4° E) and dips of pre-Tsf

7

bedrock (20-25°E) illustrated in cross section A-A'. If that is true, then the Tsf

preserved on the footwall block is likely associated with the latter half of Rio

Grande rifting and probably middle to late Miocene in age.

Two long, west-down faults are present in the quadrangle that strike north-

south. Near the western quadrangle boundary lies the Willow Draw fault

(Figures 1-4). This fault experienced as much as 6 m of vertical movement after

the development of the Cuchillo surface ca. 780 ka, as evidenced by the height of

fault scarps (Figure 5) (age of Cuchillo surface from McCraw and Love, 2012;

Mack et al., 1993; 1998; Leeder et al., 1996; Seager and Mack, 2003; Mack et al.,

2006). The fault zone associated with the Willow Draw fault is exposed at three

localities, where the fault dips west 78-82° (Figures 2-4). Slickenside striations at

two of these localities indicate a minor component of left-lateral (sinistral) slip,

making this an oblique-slip, normal fault (Figures 2 and 4). The other long fault is

found near Interstate 25 and called the Mud Springs fault. Surface fault scarps

associated with this feature are only about 2 m tall or less. However, well data

(cross section A-A') and gravity data (Gilmer et al., 1986) indicate at least 3600 m

of west-down, stratigraphic displacement of Paleozoic bedrock units below the

Palomas Formation. The Mud Springs fault bounds the west side of abedrock

high that continues southward to the Mud Springs Hills.

8

Figure 2. Photograph of the Willow Draw fault, where exposed at the foot of the slope on the south side of Monticello Canyon. Here, the fault plane strikes 349° and dips 69° W. Slickenside lineations plunge 65-69° SW along a trend of 230-239°. Kinematic data here and to the south indicate a component of left-lateral slip along this predominately west-down normal fault.

9

Figure 3. Photograph of the Willow Draw fault, where exposed in Willow Springs Draw near the southern boundary of the quadrangle. View is to the south. The fault zone consists of two faults, marked by arrows, bounding a 50-60 cm-wide, slightly deformed sliver of Palomas Formation sandy gravel. The eastern bounding fault is located immediately to the left of the rock hammer. Throw is down-to-the-west. Note the rotated clasts along the two faults and the drag folding on either side of the fault zone.

10

Figure 4. Another view of the Willow Draw fault, located 1.5 km north of the exposure illustrated in Figure 3. The fault zone is manifested by a 15-35 cm-wide damage zone containing thin (<1 cm wide) clay cores. The fault plane strikes 006° and dips 78°E. Trend and plunge of slickenside lineations average 247°\68° SW, consistent with a minor component of left-lateral slip along this predominately west-down, normal-slip fault.

Figure 5. Looking east at the 6.5 m (20-22 ft) tall fault scarp created by west-down movement along the Willow Draw fault. Photograph taken ~1 km (0.6 mi) southwest of Monticello Canyon.

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STRATIGRAPHY AND GEOLOGIC HISTORY

Stratigraphy is the geologic discipline that studies the characteristics of layered

rocks, especially the temporal and spatial relationships between various

lithologic units (some of which are formally named as specific geologic

formations). Lithologic units on this quadrangle are recognized largely by

differences in physical characteristics of the rocks (such as color, texture,

cementation, composition, and deformation differences). The lithologic units can

be divided into subsurface bedrock units, volcanic rocks, basin-fill associated

with the Rio Grande rift, and Quaternary deposits post-dating the aggradational

culmination of Rio Grande rift basins. Here, we summarize the salient features of

these four general subdivisions and illustrate some of the units using

photographs. More details of these units are presented in Appendix 2 and also in

the map legend.

Subsurface bedrock units

Subsurface bedrock units are illustrated in cross section A-A.' Here, we

summarize these units and their relation to the ancient geologic history of the

area. More detail regarding the geologic history of the Proterozoic, Paleozoic,

and Mesozoic and can be found in various papers presented by Mack and Giles

(2004).

Proterozoic

The oldest rocks consist of crystalline basement originally deposited in the

Proterozoic (within 700 to 2000 million years ago). These rocks, which include

quartzite, schist, amphibolite, and gneiss, are complexly contorted and interlayed

as a result of tectonic events that occurred during this time (Maxwell and

Oakman, 1990; Jahns et al. 1978, and Nelson et al., 2012).

12

Paleozoic rocks

Sedimentary rocks deposited in the Paleozoic and Mesozoic are much less

deformed than Proterozoic rocks, with deformation being generally limited to

tilting (up to 25° to the east) and local folding near faults. The Bliss Sandstone

(40-50 m thick) was deposited along a transgressing shoreline in the Cambrian.

Afterwards, a thick sequence (~260-270 m-thick) of strata dominated by

limestone and dolomite was deposited under relatively shallow seas in the

Ordovician. Deposition became more clastic in the Devonian and was

characterized by 30-40 m accumulations of shale and siltstones. Following the

development of a disconformity, about 540-550 m of interbedded limestones and

shales were deposited in the Pennsylvanian (Red House, Nakaye, and Bar B

Formations). Reddish clastic sedimentation largely laid down by rivers, whose

lower and upper parts contain interbedded limestones associated with periodic

advances of seas, followed in the early Permian; this package is represented by

the Bursum, Abo, and Yeso Formations (oldest to youngest) and is about 520-540

m thick. Marine conditions and limestone-dominated deposition returned in the

late Permian, marked by the 210-230 m-thick San Andres Formation. The

thicknesses and descriptions of the aforementioned Paleozoic strata are from

Jahns et al. (1978), Maxwell and Oakman (1990), Lozinsky (1985), and Lucas et al.

(2012) -- see Appendix 2 for more detailed attribution of source data with specific

lithologic units.

Mesozoic rocks

Between preserved Paleozoic and Mesozoic rocks lies an unconformity whose

lacuna spans ~170 million years, during which uplift and erosion occurred in the

13

Late Jurassic-Early Cretaceous (Bilodeau, 1986; Dickinson and Lawson, 2001).

After ~100 million years ago, Late Cretaceous rocks were laid down in a foreland

basin, complementary to the Sevier fold and thrust belt, immediately prior,

during, and following the presence of the Western Interior Seaway (Seager and

Mack, 2003; Jordan, 1981; Lawton, 1985 and 1994; Heller et al., 1986; DeCelles and

Currie, 1996). Late Cretaceous rocks generally lack limestone and include the

Dakota Sandstone (immediately pre-dating the sea), Mancos Shale and Tres

Hermanos Formations (deposited during sea-level fluctuations while the sea was

present), and the Crevasse Canyon and McRae Formations (deposited after the

sea retreated). These rocks are probably relatively thin on most of the quadrangle

but thicken towards the eastern quadrangle boundary (~900-920 m thick, cross

section A-A'). The relative thinness of these rocks is attributed to erosion that

occurred during tectonic uplift and compressional faulting associated with the

Laramide orogeny. This orogeny was concomittant with McRae Formation

deposition, based on evidence in the Caballo Mountains to the south of the study

area (Seager and Mack, 2003). Note that thicknesses and descriptions of

Mesozoic strata are from Seager and Mack (2003) and Lozinsky (1985) -- see

Appendix 2 for more detailed attribution of source data with specific lithologic

units.

Volcanic rocks

Volcanic rocks are only exposed in hills near the northern quadrangle border.

These hills include the Sierras Mediano and Huerfano Hill. The Vicks Peak Tuff

underlies both of these hills. This tuff was emplaced during a 28.8 Ma (millions

of years old) caldera explosion associated with the Nogal caldera; Furlow, 1965;

Farkas, 1969; Deal and Rhodes, 1976). The Vicks Peak Tuff is light to medium

gray and relatively fine-grained. Its sparse visible crystals include sanidine,

14

ferromagnesium minerals, and <1% quartz. Flattened pumice (fiamme) are

present. In the Sierras Mediano, the Vicks Peak Tuff is underlain by gray

andesite containing phenocrysts of plagioclase and subordinate pyroxene and

amphibole.

Basin-fill associated with the Rio Grande rift (Santa Fe Group)

The Santa Fe Group was deposited while the Palomas and Engle Basins were

subsiding during the late Oligocene through early Pleistocene. It includes two

deposits separated by a likely unconformity developed during the latest Miocene

to earliest Pliocene. Above the unconformity lies the Palomas Formation and

below lies undifferentiated Santa Fe Group strata (Tsf). The latter consists of

coarse channel-fills interbedded with tan to brown mudstones and clayey-silty,

very fine- to fine-grained sandstones. The coarse channel-fills consist of

sandstone and gravelly sandstone, where the gravel include pebbles and cobbles.

This older basin-fill unit (Tsf) is more consolidated and tilted than the younger

Palomas Formation. Using geophysical logs and drill cuttings from oil

exploratory wells, Tsf was subdivided on the footwall of the Mud Springs fault

according to texture (cross-section A-A'). Here, a finer-grained unit appears to be

sandwiched between overlying and underlying coarser units. Correlations of

these subunits between the West Elephant Butte Federal No. 1 well and the

Gartland 1 Brister well suggests apparent eastward dips of 2-4°E (decreasing up-

section) and that its basal contact has an apparent dip of 5°E. Unit Tsf is greater

than 1880 m on the hanging wall of the Mud Springs fault, according to

interpretations of the Gartland 1 Garner exploratory well by Lozinsky (1987).

The Palomas Formation was deposited on top of Miocene-age Santa Fe Group in

the Pliocene to early Pleistocene and is extensively exposed in the quadrangle.

15

The term "Palomas" was first applied to outcrops of upper Santa Fe Group basin

fill by Gordon and Graton (1907), Gordon (1910), and Harley (1934); Lozinsky

and Hawley (1986) provide more information regarding the usage of the term

since these early works. Lozinsky and Hawley (1986) formally defined the

Palomas Formation and additional detailed descriptions of the unit is found in

that work and Lozinsky (1985).

Distinguishing the Palomas Formation from younger and older deposits requires

care. It differs from younger terrace deposits by less distinct bedding and the

presence of 5-20% clay chips (up to 1 mm long) in addition to clay films on sand

grains and clasts. However, distinguishing the Palomas Formation from

underlying, Miocene-age, Santa Fe Group strata is more difficult. On-going field

study in the Monticello area suggests little to no difference in composition

between the two units, but the Palomas Formation is overall less consolidated,

less cemented (note we infer that its cementation is mostly due to clay), and

exhibits redder hues (Daniel Koning, 2013, unpubl. data). We were fortunate to

have observed a video log of a borehole from water well RG-20693 (POD 3),

located 1 km east of the western quadrangle boundary. This video log confirmed

that below the base of casing the very poorly bedded, gravelly sandstone was

more cemented and consolidated, and slightly less gravelly, than observed for

Palomas Formation outcrops on the surface. Consequently, in that area we

inferred that the less consolidated Palomas Formation extends no deeper than 85

ft (elevation of ~4810 ft), which was the depth of the base of casing. Using a

similar eastward slope as the modern Alamosa Creek, this depth/elevation for

the base of the Palomas Formation agrees well with picks of the base from the

three deep oil exploratory wells (Table 1). Interestingly, the Palomas Formation is

characterized by higher gamma ray signatures than underlying Santa Fe Group

16

strata. In the Monticello quadrangle, preliminary investigations suggests that the

Palomas Formation is in a buttress relation with older Santa Fe Group strata.

Consequently, a subsurface unconformity is inferred here too, although it likely

has a more planar shape.

Age control for the Palomas Formation is relatively good and we are able to

refine the thickness of this unit. The Palomas Formation has yielded abundant

fossils from exposures along the west side of Elephant Butte Lake (Morgan and

Lucas, 2012). The identified species from these fossils, coupled with nearby basalt

radiometric dates (Bachman and Mehnert, 1978; Seager et al., 1984) and

magnetostratigraphic data (Repenning and May, 1986; Mack et al., 1993; 1998;

Leeder et al., 1996; Seager and Mack, 2003), indicate an age range of 4.5-0.78 Ma

for the Palomas Formation. Lozinsky and Hawley (1986), who formally defined

this formation, interpret a 100-131 m thickness but Lozinsky (1985, p. 15) states

that the Palmoas Formation may be up to 180 m thick. Our study of the three

deep oil exploratory wells and the aforementioned video-logged water well (RG-

20693, POD 3) indicates that the Palomas Formation thickens from 118 m (390 ft)

to 160 m (522 ft deep) eastward across the quadrangle (Table 1).

Two depositional facies are observed in the Palomas Formation, the piedmont

and axial facies, as previously recognized in the Truth or Consequences area

(Lozinsky, 1985; Lozinsky and Hawley, 1986). The piedmont facies was

deposited by high-competency streams flowing east-southeast (based on clast

imbrication) from the southern San Mateo Mountains and the northern Sierra

Cuchillo in the Monticello area. This facies consists of sandy gravel channel-fills

interbedded with finer-grained deposits composed of fine sand and clayey-silty

fine sand with minor, scattered pebbles (Figure 6). We call the latter "extra-

17

channel sediment" because we interpret that it was deposited outside of

channels, either as gully-mouth fans (most likely) or as overbank sediment.

Extra-channel sediment is better consolidated than the coarse channel-fills. The

proportion of extra-channel deposits to coarse channel-fills increases to the east.

Extra-channel sediment is about subequal (+/-15%) to the coarse channel-fills

over most of the quadrangle, but dominates along lower Alamosa Creek (east of

Interstate 25) and in the southeastern quadrangle corner. Extra-channel sediment

is massive, exhibits minor interbedded pebbly channel-fills, and commonly

contains scattered coarse sand grains and pebble clasts. Clay-rich extra-channel

sediment is light reddish brown to reddish brown but sandy sediment is light

brown. There are 0.5% medium, tabular beds of reddish brown, clay-dominated

sediment showing ped development and illuvated clay but lacking underlying

calcic horizons (Figure 7).

Sandy gravel in the piedmont facies tends to be in 1-5 m thick, amalgamated

channel-fill complexes. The gravel is generally clast-supported, subrounded

(mostly) to subangular, poorly to moderately sorted, and composed of felsic

volcanic clasts (rhyolite and rhyolitic tuffs, mainly crystal poor with 1-2% of

gravel being moderately crystal-rich) and minor (5-15%), dark gray to brown

andesite clasts (with phenocrysts of plagioclase ± pyroxene). Clasts consist of

pebbles, subordinate cobbles, and 1-10% boulders. Channel-fills also include

minor pebbly sand. The upper 10-30 m of the piedmont facies is typically

dominated by gravel. A 1-2 m-thick petrocalcic horizon, exhibiting a stage IV

(locally stage III) carbonate morphology (Gile et al., 1966), has developed on top

of the Cuchillo surface that overlies this upper gravel (McCraw and Love, 2012;

McCraw, 2012).

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Figure 6. Outcrop of a gravelly section of the piedmont facies of the Palomas Formation. Backpack in foreground for scale. Approximate UTM coordinates: 281650 m E; 3689500 m N.

Figure 7. Outcrop illustrating the piedmont facies of the Palomas Formation. Outcrop is located on the north wall of Pinosa Canyon, about 200 m west of the eastern quadrangle border. Here, the Palomas Formation is overlain by ~2 m of unit Qao2, which commonly is typically better bedded than the Palomas Formation. The base of unit Qao2 is marked by arrows. Note the tabular, reddish brown beds of clay-dominated sediment in the Palomas Formation. These show ped development and contain evidence of illuviated clay.

19

The axial facies of the Palomas Formation is only mapped on the lower, southern

slope of Monticello Canyon within 1 km (0.6 mi) of the eastern quadrangle

boundary. It grades laterally westward into the piedmont facies. Exposures

display a thick interval (10 m or greater) of amalgamated channel-fill sands

interbedded with an interval of floodplain sediment of similar thickness (Figure

8). The channel-fill sands include minor, lenticular, cross-stratified pebbly beds

up to 2 m thick. Channel-fill sands are massive or in medium to thick, tabular

beds that are internally laminated. Lozinsky (1985) reports that the sand is

generally arkosic and pebbles consist of quartz, chert, granite, sandstone, and a

variety of volcanic rock types. Floodplain sediment is light reddish brown (5YR

6/3) and consists of clay-silt in medium to thick, tabular beds. Some zones in the

floodplain facies have abundant calcium carbonate nodules (up to 5 mm thick),

some of which appear to be associated with paleo-burrows. Fossils collected

from this general stratigraphic interval suggest a 3.0-3.3 Ma age (Morgan and

Lucas, 2012, Elephant Butte Lake fauna) or 3.0-4.5 Ma (if we extend this unit into

the subsurface).

In summary, the Santa Fe Group can be subdivided into two units on the

Huerfano Hill quadrangle. The older unit (Tsf) is not exposed, but well data

coupled with observations of outcrops outside the map area indicate that it is

more consolidated, cemented, and tilted than the younger unit. The younger unit

is the Palomas Formation, which contains a proximal facies grading eastward

into an axial facies (Lozinsky, 1985; Lozinsky and Hawley, 1986). Based on

outcrop relations on this quadrangle, the piedmont facies prograded eastward

over the axial facies during the late Pliocene-early Pleistocene.

20

Figure 8. Photograph of the axial facies of the Palomas Formation. Exposure is located 0.5 km west of the eastern quadrangle boundary, along the foot of the southern slope of Monticello Canyon. Here, sandy channel-fill deposits, interbedded with minor, lenticular pebble beds and very minor, very thin to thin clayey beds, overlies light reddish brown, tabular-bedded floodplain deposits composed of clay and silt.

Quaternary deposits post-dating the culmination of aggradation of Rio Grande

rift basins

Most of the map units on the Huerfano Hill quadrangle are of various

Quaternary units that post-date the Palomas Formation. In the northwest part of

the quadrangle lie extensive veneers of piedmont sediment, interpreted to be

middle-late Pleistocene and Holocene in age, which overlie or are buttressed

against the Palomas Formation. Most other Quaternary units are found in incised

21

canyons, either as terrace deposits, alluvial fan deposits (only differentiated in

Monticello Canyon), or a valley-floor deposits. These three groupings are

successively described below.

Terrace deposits

Six terrace deposits were differentiated in Monticello Canyon (Qt1 through Qt6),

with Qt1 being the oldest and highest terrace. All are composed of sandy gravel

(mostly pebbles and cobbles with lesser boulders). In other drainages, two to

three deposits of older alluvium (Qao1 through Qao3, with Qao1 being the oldest)

are present, generally forming terraces and all composed of sandy gravel. Qao3

likely correlates to terrace Qt6, Qao2 correlates to either Qt5 or Qt4, and Qao1

correlates to Qt4, Qt3, or Qt2 (see map correlation chart). In Monticello Canyon,

terrace deposits Qt1 through Qt2 are only found within 2.2 km (1.4 mi) of the

western quadrangle border; they probably formed in the earlier half of the

middle Pleistocene.

Qt3 and Qt4 are more extensive than higher terraces and found in close vertical

proximity to each other. Unit Qt3 is subdivided into two subunits (Qt3a and Qt3b)

(Figures 9-10). The surfaces (treads) of Qt3 and Qt4 lie 36-50 m above the modern

valley floor. Soils are marked by distinctive, relatively thick, illuviated clay

horizons underlain by calcic soils with stage III to IV carbonate morphology

(Figure 11). Surface clasts are weakly to moderately varnished. These two

terraces were probably formed during glacial-interglacial climate cycles in the

latter half of the middle Pleistocene, perhaps at 300-350 ka for Qt3 (latter half of

marine oxygen isotope stage (MOI) stage 10 and first half of MOI stage 9) and

200-270 ka for Qt4 ((latter half of marine oxygen isotope stage (MOI) stage 8 and

first half of MOI stage 7).

22

Figure 9. Sandy gravel associated with the Qt3b terrace, whose base is marked by

arrows. The Palomas Formation underlies this boulder-rich terrace deposit.

23

Figure 10 (previous page). Photograph depicting the Qta4 terrace deposit

overlying finer sandy gravel and gravelly sand of the Palomas Formation. Qta4 is

2.5 m (8 ft) thick and its base is denoted by arrows.

Figure 11 (next page). Photograph illustrating the contact between terrace

deposit Qta4 and the underlying Palomas Formation. The contact coincides with

the base of the hammer handle. Here, the Palomas Formation is coarser than

Qta4, which is unusual and probably best explained by the extreme lateral

(northerly) position of this Qta4, exposure (approx. UTM coord: 280200 m E,

3690200 m N). Qta4 contains significant illuviated clay. In this and other terraces,

calcium carbonate commonly accumulates around the basal contact of the terrace

deposit. Here, the calcium carbonate is ~20 cm thick and exhibits a stage III

carbonate morphology.

24

Qt5 is notably lower than Qt4. The Qt5 tread is 9-18 m above modern grade,

whereas the Qt4 tread is 36-39 m above modern grade. Terrace Qt5 is a suite of

25

four strath terraces between Interstate 25 and the western quadrangle border,

each having a sandy gravel deposit a few meters thick. However, near Interstate

25 and eastward to the eastern quadrangle boundary Qt5 is a single fill terrace

exhibiting thicknesses of 4-12 m (Figure 12). The surface of Qt5 is broad in the

middle and eastern parts of Monticello Canyon on this quadrangle. Distinctive

alluvial fan deposits belonging to Qf5 have prograded over the originally broader

terrace tread. The gravel sizes of Qt5 may be a somewhat coarser than those of

Qt4 and Qt3. The Qt5 surface is subjected to more sheetflooding than the older

terraces, probably due to higher surface discharge from large side drainages

associated with the Qf5 alluvial fans, and clast varnishing is slightly weaker on

the Qt5 surface compared with the surfaces of Qt4 and Qt3. The soil of Qt5 is

characterized by 35-55 cm-thick illuviated clay horizon(s) overlying 10-53 cm-

thick calcic horizon(s) possessing a stage I to II+ carbonate morphology (McCraw

and Williams, 2012). We agree with the interpretations of McCraw and Williams

(2012) that Qt5 likely formed in the latter half of MOI stage 6 and the first part of

MOI stage 5.

The lowest correlated terrace deposit along Alamosa Creek, Qt6 is mapped only

in the western part of Monticello Canyon. There, we subdivide it into two strath

terraces, each being 1-3 m thick. The gravel in terrace Qt6 appears to be of similar

coarseness as that in Qt5. Soil development is characterized by 35-40 cm-thick

illuviated clay horizons underlain by clacic horizon(s) with stage I carbonate

morphology (McCraw and Williams, 2012). Similar to McCraw and Williams

(2012), we interpret a late to latest Pleistocene in age based on soil development

and its stratigraphic position above Holocene valley-bottom alluvium and below

terrace Qt5.

26

Figure 12. Exposure of the Qt5 terrace deposit immediately west of Interstate 25.

Here, it is about 12 m (40 ft) thick and composed of sandy gravel. A degraded

calcic horizon is preserved at the surface and exhibits a stage II to II+ carbonate

morphology.

Alluvial fan deposits

Distinctive alluvial fan deposits have prograded across the terrace treads of Qt3,

Qt4, Qt5, and Qt6. These alluvial fans are called Qf3, Qf4, Qf5, and Qf6,

respectively, and their surfaces grade to the tread of the underlying terrace

deposit. Qf5 is the most extensive of the fan deposits and is relatively thick (2-12

m). The alluvial fans are composed of sandy gravel and sand. Their surface

characteristics (i.e., clast varnishing and desert pavement development) are

comparable to surfaces on the adjoining terrace tread.

27

Valley-floor deposits

The floors of canyons are underlain by Holocene alluvium. This alluvium

underlies modern channels and low-level terraces alongside modern channels.

The higher of the low-level terraces (Qay, Qay1, Qay2) lie <3 m above modern

stream grade. These are composed of interbedded sandy gravel, pebbly sand,

and sand (Figure 13). Clasts are dominated by pebbles with subordinate cobbles

(30-40%) and lesser boulders (~10%). Sand and pebbly sand beds may be massive

and contain minor, lenticular interbeds of pebbly sediment; massive beds are

typically dominated by fine sand and clayey-silty fine sand, with minor (est. 10-

30%) medium- to very coarse-grained sand and lesser (1-10%) pebbles scattered

in the finer-grained matrix (Figure 14). Except where eroded, the tops of the

higher low-level terraces (Qay, Qay1, Qay2) exhibit a weak soil marked by

calcium carbonate accumulation (stage I, locally stage II carbonate morphology)

overlain locally by slightly darkened A horizons (where minor organic matter

has accumulated). Surface clasts of the higher low-level terraces are non- to

weakly varnished and subtle bar-and-swale topography may still be evident.

28

Figure 13. Photograph illustrating Qay2 overlying Qay1. Contact is marked by the

arrows. See Appendix 2 for more detail regarding these two units.

29

Figure 14. Photograph illustrating Qay2 overlying Qay1. Contact is marked by the

arrows. Underlying Qay1 is mostly massive sand with minor (20-30%) pebbly

beds that are very thin to medium and lenticular. The sand is mostly fine-grained

but contains 10-30%, scattered, medium- to very coarse sand grains and 1-10%

pebbles. Exposure is 2 m tall.

The surfaces of historical terraces (Qah) lie 0.2-1.0 m below the surfaces of Qay,

Qay1, and Qay2. The treads of historic terraces are <2 m above modern stream

grade. The overall sediment texture of historic terraces is coarser-grained than

higher valley-bottom terraces (Qay, Qay1, and Qay2) (Figure 15). Historic

surfaces exhibit muted bar and swale topography and channel forms; generally

there is less than 30 cm of surface relief and vegetative cover is sparse to

moderate (Figure 16). Modern alluvium (Qam) consists of sand and gravel

underlying very low surfaces astride active channels. This unit is inferred to

30

receive runoff from high-precipitation, monsoonal storms that likely have multi-

year to decadal recurrence intervals. Bar and swale topography and channel

forms are sharp, with 30-80 cm of typical surface relief, and vegetation is sparse

(Figure 17). The sand and gravel of active alluvium (Qaa) underlies channel

floors that are generally active on a yearly basis. Its sediment is similar to that of

Qam. Neither Qam or Qaa have notable soil development. All valley-bottom

deposits are loose to weakly consolidated. They likely overlie the Palomas

Formation and are probably <10 m thick.

Figure 15. 1.5-2.0 m-tall exposure of Historic alluvium (Qah) in Monticello

Canyon. It consists of well-beded sandy gravel and minor pebbly sand.

31

Figure 16. Top few cm of the photograph shown in Figure 15. The top of Hisotric

alluvium commonly has 1-30 cm of well-sorted, locally silty, very fine- to

medium-grained sand that is horizontal-planar laminated, low-angle cross-

laminated, or rippled-laminated -- representing overbank sediment deposited

during modern floods.

Figure 17. Surface of modern alluvium (Qam). Note the fresh bar and swale

topography (up to 60 cm tall). Sediment consists of interbedded sand and gravel

in very thin to thick, tabular to lenticular beds.

32

HYDROGEOLOGY

This project did not involve any detailed ground water study. Nonetheless, we

think it is worthwhile to share three cursory observations and postulations

regarding groundwater flow. First, no streams or active springs are present in the

study area. Surface runoff probably occurs only in response to high-precipitation

events, although it is conceivable that Alamosa Creek may experience prolonged

surface discharge in extremely wet years. Second, inspection of well records

(spanning several decades) in Monticello Canyon indicate that the potentiometric

surface is less than 150 ft deep. Third, we postulate that two aquifers are present

in the Santa Fe Group basin-fill under Monticello Canyon; this interpretation is

based on inspection of well records in Monticello Canyon, oral conversations of

residents, and geologic findings presented in this report. The higher aquifer is

perched (at least locally), probably of limited extend, and likely corresponds with

lowermost Palomas Formation strata (<85 ft deep at RG-20693_POD3 but

becoming deeper to the east). This aquifer may receive recharge via percolation

from Alamosa Creek. The deeper aquifer coincides with undifferentiated Santa

Fe Group strata below the Palomas Formation (Tsf). Uppermost Tsf strata may

be unsaturated, but deeper strata hosts ground water flow via fractures or

weakly cemented channel-fills. Groundwater levels generally rise when

saturated Tsf is encountered, indicating confined groundwater flow conditions.

Groundwater is typically warm (85-96°) in the Tsf aquifer. These temperatures

suggest relatively long and deep flow paths; they also suggest a degree of

connectivity with the geothermal system associated with Truth or Consequences.

We speculate that this geothermal system originates in the San Mateo Mountains

and generally experiences fracture-flow in pre-Santa Fe Group bedrock units

33

(Cenozoic volcanic rocks, Mesozoic rocks, and Paleozoic strata). Near Monticello

Canyon, some of the heated water may flow up into the Santa Fe Group along

fractures associated with major fault zones, such as the Willow Draw fault or the

queried east-west trending fault north of Monticello Canyon. Mixing of this

heated groundwater with groundwater derived from other sources may then

occur in the Tsf aquifer.

APPENDIX 1. MAPPING AND DESCRIPTION METHODS

The units described below were mapped using aerial photography coupled with

field checks. Stereogrammetry software recently acquired by the N.M. Bureau of

Geology (i.e., Stereo Analyst for ARCGIS 10.1, an ERDAS extension, version

11.0.4) results in relatively accurate placement of geologic contacts. Grain sizes

follow the Udden-Wentworth scale for clastic sediments (Udden, 1914;

Wentworth, 1922) and are based on field estimates. Pebbles are subdivided as

shown in Compton (1985). The term “clast(s)” refers to the grain size fraction

greater than 2 mm in diameter. Descriptions of bedding thickness follow Ingram

(1954). Colors of sediment are based on visual comparison of dry samples to the

Munsell Soil Color Charts (Munsell Color, 1994). Soil horizon designations and

descriptive terms follow those of the Soil Survey Staff (1992), Birkeland et al.

(1991), and Birkeland (1999). Stages of pedogenic calcium carbonate morphology

follow those of Gile et al. (1966) and Birkeland (1999). Description of sedimentary

and igneous rocks was based on inspection using a hand lens.

Surface characteristics aid in mapping Holocene and middle-late Pleistocene

units. Older deposits generally have older surfaces, so surface processes

dependent on age -- such as desert pavement development, clast varnishing,

34

calcium carbonate accumulation, and eradication of original bar-and-swale

topography -- can be used to differentiate terrace, alluvial fan, and valley floor

deposits. Locally, erosion may create a young surface on top of an older deposit,

so care must be exercise in using surface characteristics to map Quaternary

deposits.

APPENDIX 2. DETAILED UNIT DESCRIPTIONS

af Artificial fill (<80 years old) – Sand and gravel reworked by humans into

berms, levees, and road beds. Weakly to well consolidated and non-cemented.

Locally includes minor excavations. Up to 15 m thick.

Hillslope units (Quaternary)

Qc Colluvium (middle-upper Pleistocene and Holocene) – Poorly sorted,

angular to subangular, clayey-silty sand and gravel mantling middle-lower

hillsopes of Huerfano Hill, the Sierras Mediano, and along the footslopes of fault

scarps. <8 m thick.

Valley bottom units (Quaternary)

Unless otherwise noted, gravel is composed of rhyolite and minor felsic tuffs

(both mainly crystal-poor) along with 5-15% andesite. The latter is typically dark

gray and contains plagioclase ± pyroxene phenocrysts. Clasts are subrounded

(minor subangular). Sand is subrounded (minor subangular ) and a volcanic

litharenite.

35

Qsef Slopewash and sheetflood deposits associated with fault-related

depressions (upper Pleistocene to Holocene) -- Yellowish brown (10YR5/4),

massive, poorly sorted, clayey-silty very fine- to very coarse-grained sand. Minor

(~10%?), scattered very fine to very coarse-grained pebbles eroded from the

Palomas Formation. This sediment fills depressions created by hanging wall

subsidence immediately adjacent to fault scarps. Description is from ~10 cm-deep

holes exposing only the uppermost part of the unit. Thickness likely less than 6

m.

Qaa Active alluvium in active channels (<5 years old) – Sand and gravel

underlying modern channel floors that are generally active on a yearly basis, due

to runoff generated by high-precipitation storms (mostly associated with

summer monsoons). Sediment similar to that described in unit Qam. No soil

development. Generally <3 m thick, although greater thicknesses are possible

locally along Alamosa Creek.

Qam Modern alluvium (0 to ~50 years old) – Sand and gravel underlying very

low surfaces astride active channels. Unit inferred to receive runoff from high-

precipitation, monsoonal storms that likely have multi-year to decadal

recurrence intervals. Bar and swale topography and channel forms are sharp,

with 30-80 cm of typical surface relief, and vegetation is sparse. Sediment is

commonly in very thin to thin, tabular to lenticular beds; sand is typically

horizontal-planar laminated to cross-laminated. Gravel are poorly sorted and

consist of pebbles with subordinate cobbles and boulders. Sand is grayish brown

to pale brown (10YR 5/2-6/3), fine- to very coarse-grained, and poorly to

moderately sorted within a bed. Loose and no soil development. Generally <3 m

thick, although greater thicknesses are possible locally along Alamosa Creek.

36

Qaam Active and modern alluvium, undivided (0 to ~50 years old)—

Active (Qaa) alluvium associated with channels and subordinate modern

alluvium (Qam); these two units are described above.

Qamh Modern and historical alluvium, undivided (0 to ~800 years old) –

Modern alluvium (Qam) and subordinate historical alluvium (Qah). See detailed

descriptions of those individual units.

Qah Historical alluvium (50 to ~800 years old) – Sand and gravel in valley

bottoms. Sediment is typically well-bedded, although locally it may be

bioturbated and massive near the surface. Where observed, sediment is in very

thin to medium, tabular to lenticular beds. Sandy beds are commonly internally

horizontal-planar laminated to low-angle cross-laminated. Gravel are clast- to

matrix-supported (matrix being sand), subrounded, and moderately to poorly

sorted within a bed. Gravel sizes consist of pebbles with minor cobbles (~30%)

and 5-10% boulders. Sand is brown, grayish brown, dark grayish brown, and

light brownish gray (10YR 4-6/2, 5/3), locally silty, very fine- to very coarse-

grained, and moderately to poorly sorted within a bed. Surface exhibits muted

bar and swale topography and channel forms; generally less than 30 cm of

surface relief. Sparsely to moderately vegetated and exhibits no obvious soil

development. Top of unit may contain about 1-30 cm of well-sorted, locally silty,

very fine- to medium-grained sand that is horizontal-planar laminated, low-

angle cross-laminated, or rippled-laminated; this represents overbank sediment

deposited during modern floods. In Monticello Canyon, the top of this unit is

locally overlain by coppice dunes that were not differentiated; these dunes

consist of low-angle cross-laminated, very fine- to medium-grained sand that

37

was blown out of a nearby, active channel. Tread is commonly less than 2 m

above modern grade. Loose. Base not observed in thickest deposits; possibly up

to 3-4 m maximum thickness.

Qaha Historical alluvium and active alluvium, undivided (0 to ~800 years old)

– Historical alluvium (Qah) and subordinate active alluvium (Qaa), which are

described in detail above.

Qahm Historical alluvium and modern alluvium, undivided (0 to ~800 years

old) – Historical alluvium (Qah) and subordinate modern alluvium (Qam),

which are described in detail above.

Qar Active, modern, and historical alluvium, undivided (0 to ~800 years old)

– Active (Qaa), historical alluvium (Qah), and modern alluvium (Qam) in

various proportions. These units are described in detail above.

Qahy Historical alluvium and younger alluvium, undivided (~50 to 8,000 years

old) – Historical alluvium (Qah) and subordinate younger alluvium (Qay). See

detailed descriptions of those individual units.

Qary Recent alluvium (historical + modern + active) and younger alluvium,

undivided (0 to 8,000 years old) – Recent alluvium (Qah, Qam, Qaa -- grouped

together as a “recent” deposit) and subordinate younger alluvium (Qay). See

detailed descriptions of these individual units.

Qay Younger alluvium, undivided (middle to upper Holocene) – Sand and

gravel underlying low-level terraces alongside modern arroyos. Generally

38

consists of sandy gravel and pebbly sand. Gravelly sediment is typically in very

thin to medium, vague, lenticular to tabular beds. Clasts are dominated by

pebbles with subordinate cobbles (30-40%) and lesser boulders (~10%). Gravel is

clast-supported and poorly sorted. Sand is brown to light brownish gray (7.5-

10YR 4-5/3; 10YR 6/2), very fine- to very coarse-grained, and poorly sorted. Sand

and pebbly sand beds may be massive and contain minor, very thin to medium,

lenticular interbeds of pebbly sediment; massive beds are typically dominated by

fine sand and clayey-silty fine sand, with minor (est. 10-30%) medium- to very

coarse-grained sand and lesser (1-10%) pebbles scattered in the finer-grained

matrix. Except where eroded, the top of this unit typically exhibits a weak soil

marked by calcium carbonate accumulation (stage I, locally stage II carbonate

morphology) overlain locally by slightly darkened A horizons (where minor

organic matter has accumulated). Surface clasts are non- to weakly varnished

and subtle bar-and-swale topography may still be evident. Surface exhibits a

weak clast armor. Surface stands a little higher (by 0.2-1.0 m) than the surface of

unit Qah. Loose to weakly consolidated. Typical thickness of at least 2 m but

generally the base is not exposed; estimated maximum thickness of 5-7 m.

Locally, this unit is subdivided into two subunits that are described below.

Qay2 Younger unit of younger alluvium (upper Holocene) –

Interbedded sand, pebbly sand, and sandy pebbles-cobbles underlying

low-level terraces alongside modern arroyos. Locally overlies Qay1 across

a sharp, scoured disconformity. Bedding is variable, but is typically

distinct in very thin, tabular to lenticular beds; locally, bedding is massive.

Gravel is dominated by pebbles and cobbles, is clast- to matrix-supported,

and may exhibit imbrication. Sand is grayish brown to brown to light

brown (7.5YR 5/3-6/4; 10YR 5/2-3), fine- to very coarse-grained, locally

39

silty, and moderately to poorly sorted within a given bed. Fine sand beds

typically contain sparse, scattered, coarse sand grains. Upper 5-10 cm is

commonly finer-grained than lower sediment, with abundant very fine- to

fine-grained sand and lesser silt (~10%) that was transported to the surface

via eolian processes. This upper layer is brown (7.5-10YR 5/3). Within the

fine sand is minor, scattered medium to very coarse sand grains and

matrix-supported, poorly sorted pebbles. Overall, this upper layer is

moderately to poorly sorted. Compared to unit Qay1, this unit has weaker

degrees of calcium carbonate accumulation (stage I carbonate

morphology) but commonly exhibits a slightly darkened A horizon (dark

brown to brown, 7.5YR 3-4/3) at the top of its weak soil profile (commonly

1-10 cm thick). Peds are of weak to moderate grade, fine to coarse,

subangular blocky (locally somewhat platy), slightly hard, and lack clay

films. Surface clasts are non- to weakly varnished; surface clast armor is

weak to moderate. Surface lies 0.1-1.0 m above the modern channel and

retains subdued evidence of bar and swale topography. 1-2 m thick.

Qay1 Older unit of younger alluvium (middle to upper Holocene) –

Sand and gravel underlying low-level terraces alongside modern arroyos

whose treads are slightly higher than those associated with Qay2. Gravel-

dominated strata are typically clast-supported and in very thin to

medium, tabular to lenticular beds. Clasts include pebbles with

subordinate cobbles (35-40% or less) and lesser boulders (~10%). Gravel is

variably imbricated and poorly sorted. Sand associated with the gravel is

light brownish gray (10YR 6/2) to brown (7.5YR 4/3 to 10YR 5/3), locally

silty, very fine- to very coarse-grained, loose, and poorly sorted. Massive

sand and pebbly sand is common in this unit; this massive sediment

40

contains minor (20-30%) pebbly interbeds (typically very thin to medium,

lenticular beds). This sand is brown (7.5-10YR 5/3) to reddish brown (5YR

5/4), variably silty (<10%), and dominated by fine- to medium-grained

sand with minor coarser sand grains and pebbles scattered in the finer

matrix. In the soil, there is sparse, thin clay films on the clasts. Compared

to Qay2, this unit exhibits more visible evidence of calcium carbonate

accumulation (stage I to II). Calcium carbonate coats parts of clast

surfaces, commonly at depths of 20-40 cm, but visible evidence of calcium

carbonate in the sandy matrix is variable. Weakly consolidated. Surface is

1 to 3 m above that of modern stream grade. No to slight varnishing and

no reddening of the surface clasts. 1-5 m thick.

Qaya Younger alluvium and active alluvium, undivided (0 to 8,000 years old)

– Younger alluvium and subordinate active alluvium, the latter typically

occupying a deeply incised channel. See descriptions for Qay and Qaa above.

Qayh Younger alluvium and historic alluvium, undivided (50 to 8000 years

old) – Younger alluvium and subordinate historic alluvium. See descriptions for

Qay and Qah above.

Qayr Younger alluvium and recent (historical + modern +active) alluvium,

undivided (800 to 8000 years old) – Historic and modern alluvium (Qah, Qam,

Qaa -- grouped together as a “recent” deposit) and subordinate modern alluvium

(Qay) deposited on alluvial fans in Monticello Canyon. See detailed descriptions

of these individual units. Up to ~10 m thick.

41

Terrace deposits and older alluvium

Unless otherwise noted, gravel is composed of rhyolite and minor felsic tuffs

(mainly crystal-poor) along with 5-15% andesite. The latter is typically dark gray

and contains plagioclase ± pyroxene phenocrysts. Clasts are typically

subrounded. Sand is subrounded (minor subangular ) and a volcanic litharenite.

Terrace deposits associated with Alamosa Creek

Note that we mapped terrace deposits, as opposed to mapping terrace treads

(upper surface of a terrace). So contacts on this map delineating terraces coincide

with the terrace strath (base of deposit) and the toe of the riser to the next higher

terrace level. Note that McCraw and Williams (2012) mapped terrace treads, and

this is one reason that their contacts do not coincide with ours. Terraces mapped

by McCraw and Williams (2012) that lie above our Qta1 were interpreted by us

to be likely erosional surfaces lacking an associated deposit, so they were not

shown on our map.

Qtu Undifferentiated Alamosa terrace deposit (Pleistocene) – Sandy gravel

terrace deposit that was not correlated. 1-3 m thick.

Qt6 Lowermost Alamosa terrace deposit (uppermost Pleistocene) – Sandy

gravel occurring as 2-3 m-thick strath terraces. Gravel consists of well-graded

pebbles through fine boulders and is clast –supported. Sand is brown (10YR 5/3),

very fine- to very coarse-grained (mostly coarse- to very coarse-grained), and

poorly sorted. McCraw and Williams (2012) note reddish, illuviated clay (Bt)

horizons in this unit that exhibit total thicknesses of 35-40 cm. The Bt horizons

overlie a 10 cm-thick calcic soil horizon manifesting a stage I carbonate

42

morphology (McCraw and Williams, 2012). This terrace largely coincides with

the Qt6 and Qt6a terrace of McCraw and Williams (2012). 1-3 m thick. Locally,

Qt6 can be subdivided into two subunits:

Qt6b Lower subunit of the lowermost terrace deposit along

Alamosa Creek (uppermost Pleistocene) – – Sandy gravel similar to that

described for unit Qt6 above. Tread lies about 5-7 m above the modern

stream grade.

Qt6a Upper subunit of the lowermost terrace deposit along

Alamosa Creek (uppermost Pleistocene) – Sandy gravel whose tread lies

about 2 m above the tread of terrace Qt6b. Probably 1-2 m thick.

Qt5 Upper lower Alamosa terrace deposit (upper-middle to upper

Pleistocene) – Sandy gravel underlying an extensive terrace along Alamosa

Creek. Deposit contains very thin to medium, tabular to irregular to lenticular

beds; 1-3% planar-cross-stratified, very thin foresets <1 m thick. Gravel is clast-

supported and imbricated to the east. Clast sizes range from pebbles to boulders

(mostly pebbles and cobbles, with 10-20% boulders). Clasts are subrounded to

rounded and poorly to very poorly sorted. The sand is brown (7.5YR 5/4; 10YR

5/3), very fine- to very coarse-grained (mostly medium- to very coarse-grained),

and moderately to poorly sorted. Less than 7% clay chips and argillans (clasts

and grains are mostly NOT covered by clay films). Less than 10% overbank

sediment composed of clay, silt, and very fine- grained sand (in intervals 1 m

thick or less). Weakly consolidated and non-cemented. Surface is subjected to

sheetflooding and the development of the preserved soil is variable (stage I to

stage III carbonate morphology, but mostly stage II to II+). Detailed soil data for

43

the Qt5 terrace can be found in McCraw and Williams (2012). These workers

observe 35-55 cm-thick illuviated clay horizon(s) overlying 10-53 cm-thick calcic

horizon(s) possessing a stage I carbonate morphology (soil pits CA5 and CA6b,

note that we correlate our Qt5d with their Qt6b). Surface typically exhibits

moderate to weak reddening and varnishing of clasts, although near the western

quadrangle boundary Qt5 lacks a desert pavement and clasts are not varnished.

This unit is a fill terrace in the vicinity of Interstate 25 and downstream of the

highway, where it has a thickness of 4-12 m, but upstream the terrace diverges

into four strath terraces whose deposits are relatively thin (1-2 m). To the east,

the lower contact is highly scoured and exhibits meter-scale relief. To the west,

the lower contact is scoured but more planar. Locally, Qt5 can be subdivided into

four subunits:

Qt5d Lowest subunit of the upper lower terrace deposit along

Alamosa Creek (upper-middle to upper Pleistocene) – Sandy gravel

whose sediment resembles that of units Qt5b and Qt5a. Not described in

detail. Tread lies 2 m above the tread of Qt6a. Correlates to the Qt6b

terrace of McCraw and Williams (2012). Thickness not accurately

measured but likely 1-2 m thick.

Qt5c Lower middle subunit of the upper lower terrace deposit

along Alamosa Creek (upper-middle to upper Pleistocene) – Sandy

gravel whose sediment resembles that of units Qt5b and Qt5a. Not

described in detail. Tread lies 1-2 m above the tread of Qt5d. Correlates to

the Qt6b and Qt6c terraces of McCraw and Williams (2012). Thickness not

accurately measured but likely 1-2 m thick.

44

Qt5b Upper lower subunit of the upper lower terrace deposit

along Alamosa Creek (upper-middle to upper Pleistocene) – A coarse,

very poorly sorted deposit composed of sandy gravel (est. 50-60% pebbles,

30-40% cobbles, and 10-20% boulders). Surface is similar to that described

on unit Qt5a. Tread lies ~3 m above the tread of Qt5c. Correlates to the

Qt5 terrace of McCraw and Williams (2012). Deposit is 1-2 m thick.

Qt5a Highest subunit of the upper lower terrace deposit along

Alamosa Creek (upper-middle to upper Pleistocene) – A relatively coarse

deposit composed of very poorly sorted, sandy gravel (estimated 40-50%

pebbles, 30-40% cobbles, and 15-30% boulders. Surface clasts have a weak-

moderate desert pavement (weakly to moderately developed clast armor

and Av peds) and a weak-moderate varnishing of clasts. Tread lies about

2 m above the tread of Qt5b. Correlates to the Qt5 terrace of McCraw and

Williams (2012). Deposit is ~2 m thick.

Qt4 Lower middle terrace deposit along Alamosa Creek (middle Pleistocene)

– A sandy gravel that exhibits vague, very thin to medium, tabular (mostly) to

lenticular beds; also locally very thinly bedded, planar-cross-stratified. Gravel

consists of pebbles with 10-50% cobbles and 1-25% boulders. Generally less

bouldery than lower terrace deposits (Qt5 and Qt6). Gravel are clast-supported,

subrounded, and very poorly to moderately sorted. Clast imbrication is to the

east-southeast. Sand is brown to strong brown to light brown (7.5YR 5/4-6, 6/4),

very fine- to very coarse-grained (mostly medium- to very coarse-grained),

subangular to rounded (mostly subrounded), and poorly to moderately sorted.

<10% clay films and clay chips. Surface gravel is weakly to moderately varnished

and moderately reddened; moderate desert pavement development. Soil marked

45

by a thick (up to 150 cm) illuviated clay horizon underlain by a calcic horizon

exhibiting stage I+ to IV carbonate morphology; the calcic horizon commonly

coincides with the base of the terrace deposit. The illuviated clay horizon is

strong brown (7.5YR 4-5/6) to reddish brown-yellowish red (5YR 4/6-5/4) and is

manifested by faint to prominent coatings covering 5-50% of grain and clast

surfaces; most illuviation is concentrated 10-40 cm below ground surface.

Generally no Holocene surface deposits on its upper surface. Weakly to

moderately consolidated. Looser and browner than underlying Palomas

Formation. Tread lies about 19-20 m above the Qt5a tread and 36-39 m above

modern stream grade. Correlates to the Qt4a terrace of McCraw and Williams

(2012). Thickness of 1.5 to 2.5 m.

Qt3 Upper middle terrace deposit along Alamosa Creek (middle Pleistocene)

– Tread is 2.5 m above the tread of unit Qt4. Unit correlates to Qt4b of McCraw

and Williams (2012). Qt3 appears to be slightly thicker than Qt4 and can be

subdivided into two subunits:

Qt3b Lower subunit of the upper middle terrace deposit along

Alamosa Creek (middle Pleistocene) – Sandy gravel that is poorly

exposed. Gravel consists of pebbles with 30% cobbles and 5% boulders.

Clasts are subrounded and poorly sorted. Top soil marked by significant

clay accumulation and probably has what can be classified as an argillic

horizon (Soil Survey Staff, 1992). Clay films are distinct to prominent and

cover 30-60% of grains and clasts. Sand is fine- to very coarse-grained and

poorly sorted. Clay films inhibit identification of grain composition, but

based on adjoining terraces the sand is likely a volcanic litharenite.

Weakly (mostly) to moderately consolidated. Near base of the deposit is a

46

40-50 cm-thick petrocalcic horizon (stage III+ carbonate morphology).

Surface lies 3-8 m above the surface of Qt4. Correlates with Qt4 of

McCraw and Williams (2012) upstream of Questa Blanca Canyon and with

Qt4b of McCraw and Williams (2012) downstream of Questa Blanca

Canyon. 1-5 m thick.

Qt3a Higher subunit of the upper middle terrace deposit along

Alamosa Creek (middle Pleistocene) – Sandy gravel roughly similar to

that in the Qta3b deposit. Not described in detail. Correlates with the

Qt3a terrace of McCraw and Williams (2012) downstream of Questa

Blanca Canyon and with Qt4 of McCraw and Williams upstream of

Questa Blanca Canyon. Tread of Qt3a typically lies 4-6 m above the tread

of Qt3b, increasing to ~8 m in a downstream direction. 1-2 m thick.

Qt2 Lower upper terrace deposit along Alamosa Creek (middle Pleistocene)

– No exposure observed but deposit is probably less than or equal to 1 m thick.

The tread exhibits a stage IV petrocalcic horizon which is buried by gravelly

colluvium and slopewash. Correlates to units Qt3a and Qt3 of McCraw and

Williams (2012).

Qt1 Uppermost terrace deposit along Alamosa Creek (middle Pleistocene) –

No exposure observed but deposit is probably less than or equal to 1 m thick.

Correlates to unit Qt3t of McCraw and Williams (2012).

47

Older alluvium associated with streams other than Alamosa Creek

Qao Older alluvium, undivided (middle to upper Pleistocene) – Relatively

thin alluvium underlying terraces alongside drainages other than Alamosa

Creek. Surfaces are typically moderately varnished, lack bar-and-swale

topography, and exhibit topsoils with strong calcium carbonate accumulations

(stage II+ to III carbonate morphology). <2 m thick. Typically three terrace levels

are present in a given drainage, which are described below:

Qao3 Lower unit of older alluvium (middle to upper Pleistocene) – Sandy

gravel not described in detail. Probably correlates to Qt6 or possibly Qt5. Tread

is located 2-4 m below Qao2 and 2-6 m above modern stream grade, with the

vertical distance between Qao3 and modern stream grade increasing in a

downstream direction. Probably 1-3 m thick.

Qao2 Middle unit of older alluvium (middle to upper Pleistocene) – A

prominent strath terrace found in most canyons. The deposit consists of

distinctly bedded, loose, sandy gravel displaying thin to medium, tabular,

lenticular, or cross-stratified bedding. Locally exhibits fining-upward trends.

Gravel contains pebbles with 1-10% cobbles (up to 10 cm long); boulders are

absent to very sparse. Clasts are subangular to rounded, moderately to poorly

sorted, clast-supported, and poorly to well-imbricated. Sand in the matrix

exhibits reddish colors, mostly yellowish red (5YR 5/6-8) to reddish yellow (5YR

6/6) to pink (5YR 7/4). Sand is variably clayey-silty and fine- to very coarse-

grained, subangular to rounded, and poorly sorted. Its surface lies 3 to 9 m above

modern stream grade. Terrace tread and modern stream grade diverge in a

downstream direction. Top soil exhibits a horizon of illuviated clay (Bt)

48

overlying a calcic horizon (Bk) with a stage II to III carbonate morphology.

Illuviated clay is less than 10% of the non-gravel fraction and manifested by few

to common (5-50% of grain or pore surface), faint to distinct coats on grains,

bridges between grains, and coating pores. Clay films are slightly browner than

the clay films and clay chips found in the Palomas Formation (unit QTpp), and

generally less than 10% clay. Unit likely correlates to Qt4 or Qt5. 1-3 m thick.

Qao1 Upper unit of older alluvium (middle Pleistocene) – More discontinuous

than unit Qao2. The deposit is not exposed and thin (probably less than 1 m thick

in most places), with the existence of a terrace deposit questionable in many

places. Surface typically lies 3-4 m above the Qao2 surface. The few exposures

generally show a sandy gravel texture (sand is 5-30% of deposit). Bedding is

vague and planar. Gravel is comprised of well-graded to fine-dominated pebbles

with 2-10% cobbles (up to 25 cm long) that are clast-supported, subangular to

subrounded, and moderately to very poorly sorted. Clasts are moderately to well

imbricated. Matrix is brown to light brown (7.5YR 4/3-6/4) to reddish yellow

(5YR 6/6), silty to slightly silty fine- to very coarse-grained sand that is poorly

sorted. The Qao1 tread lies 20-40 ft above that of Qao2. Top soil has a strong

calcic horizon displaying stage III to III+ carbonate morphology. Locally, an

illuviated clay horizon overlies the calic horizon (manifested by faint clay bridges

and films covering 5-50% of gravel surfaces). Surface clasts exhibit reddening.

Terrace tread and modern stream grade diverge in a downstream direction. Unit

likely correlates to Qt3 or Qt4. 1-3 m thick.

49

Alluvial fan units

Qfm Modern-active alluvium in alluvial fans flanking Monticello Canyon (0

to ~50 years old) – Unit is similar to that described in Qam and Qaa but is found

on alluvial fans that flank Monticello Canyon. In aerial view, this unit generally

appears wedge- or pie-shaped, with the apex of the triangle coinciding with the

downstream terminous of an upstream alluvial fan channel. <3 m thick.

Qfmh Modern-active and historic alluvium in alluvial fans flanking

Monticello Canyon, undivided (0 to ~800 years old) – Modern-active alluvium

(Qfm) and subordinate historical alluvium (Qfh) deposited on alluvial fans in

Monticello Canyon. See descriptions of Qfm and Qfh. <3 m thick.

Qfh Historical alluvium in alluvial fans flanking Monticello Canyon (0 to

~50 years old) – Unit is similar to that described in Qah, but is found on alluvial

fans that flank Monticello Canyon. The amount of area on the fan that this unit

covers is variable. <3 m thick.

Qfhm Historic and modern-active alluvium in alluvial fans flanking

Monticello Canyon, undivided (0 to ~800 years old) – Historic alluvium (Qfh)

and subordinate modern alluvium (Qam) deposited on alluvial fans in

Monticello Canyon. See descriptions of Qfh and Qfm above. <3 m thick.

Qfry Recent alluvium (historical + modern-active) and younger alluvium in

alluvial fans flanking Monticello Canyon, undivided (0 to ~800 years old) –

Historic and modern alluvium (Qfh and Qfm, grouped together as a “recent”

50

deposit) and subordinate younger alluvium (Qfy) deposited on alluvial fans in

Monticello Canyon. See descriptions of Qfh, Qfm, and Qfy. Up to ~10 m thick.

Qfhy Historic and younger alluvium in alluvial fans flanking Monticello

Canyon, undivided (0 to ~800 years old) – Historic alluvium (Qfh) and

subordinate younger alluvium (Qfy) deposited on alluvial fans in Monticello

Canyon. See detailed descriptions of Qfh and Qfy. Up to ~10 m thick.

Qfy Younger alluvium in alluvial fans along the margins of Canada

Alamosa (Holocene) – Pale brown sandy gravel. Beds are very thin to medium,

tabular to lenticular to irregular to U-shaped beds. Gravel ranges from pebbles to

boulders but is mostly pebbles and cobbles. Surface soil generally manifests a

stage I carbonate morphology. On the surface, bar and swale topography is

generally muted and contains a desert pavement underlain by 2-3 cm-thick Av

peds. No varnishing of surface clasts. Up to ~10 m thick.

Qfyh Younger alluvium and historic alluvium in alluvial fans flanking

Monticello Canyon, undivided (0 to ~800 years old) – Younger alluvium (Qfy)

and subordinate Historic alluvium (Qah) deposited on alluvial fans in Monticello

Canyon. See descriptions of Qfy and Qfh above. Up to ~10 m thick.

Qfyr Younger alluvium and recent (modern + historic) alluvium in alluvial

fans flanking Monticello Canyon, undivided (0 to ~8000 years old) – Younger

alluvium (Qfy) and subordinate recent alluvium (grouped modern and historical

alluvium, Qam and Qah) deposited on alluvial fans in Monticello Canyon. See

descriptions of Qfy and Qfh above. Up to ~10 m thick.

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Qfo Older alluvium in alluvial fans flanking Monticello Canyon, undivided

(upper-middle Pleistocene to lower Holocene) – Sandy gravel and sand whose

surface clasts are varnished. 1-10(?) m thick.

Qf6 Alluvial fans graded to the lowermost terrace tread of Alamosa Creek

(uppermost Pleistocene to lower Holocene) – Sandy gravel and sand whose

surface is more or less graded to the tread of terrace Qt6. Surface clasts are

weakly varnished and bar-and-swale topography is eradicated, although large

channel-forms are preserved. Up to 10 m thick.

Qf5 Alluvial fans graded to the upper-lower terrace tread of Alamosa Creek

(upper-middle(?) to upper Pleistocene) – An extensive unit composed of sandy

gravel and sand. Fan surface is similar to the surface developed on Qt5; pebbles

are weakly to moderately varnished and boulders-cobbles are moderately

varnished (because they have been subjected to less reworking by sheetflooding).

2-12 m thick, with the thicker fans being on the south flank of Monticello

Canyon.

Qf4 Alluvial fans graded to the lower-middle terrace tread of Alamosa Creek

(middle Pleistocene) – Sandy gravel to sand. Sandy gravel is in very thin to

medium, tabular (minor lenticular) beds. Gravel consist of pebbles and minor

cobbles. Gravel is clast-supported, subrounded, poorly to moderately sorted, and

commonly imbricated parallel to local side-stream arroyos. Sand associated with

the gravel is brown (7.5YR 5/4), very fine- to very coarse-grained, subrounded to

subangular, and poorly sorted. Also locally present is massive, clayey-silty, very

fine- to fine-grained sand with minor, scattered, medium- to very coarse-grained

52

sand and 20-25% scattered pebbles. It has common colors of light brown to

strong brown (7.5YR 6/4-5/6). This finer-grained sediment is intercalated with 15-

30%, very thin to medium, lenticular beds of very fine-very coarse pebbles and

minor (1-5%) fine cobbles. Local medium to thick beds composed of sandy

pebbles to fine boulders. Top soil consists of a stage I+ to II calcic horizon that is

locally >30 cm thick. Desert pavement is similar to that developed on Qt4.

Approximately 2 m thick.

Qf3 Alluvial fans graded to the upper-middle terrace tread of Alamosa

Creek (middle Pleistocene) – Sandy gravel and sand that was not described in

detail. The associated alluvial fan progrades onto the Qt3b terrace tread tread.

Surface is roughly similar to that on Qt3b but surface varnishing is slightly less.

About 2 m thick.

Post-Palomas Formation piedmont alluvium, northwest corner of

quadrangle

Unless otherwise noted, gravel is composed of rhyolite and minor felsic tuffs

(both mainly crystal-poor) along with 1-10% andesite (commonly plagioclase-

phyric) that are angular to subrounded; andesites are typically more rounded

than felsic clasts. Sand is a volcanic litharenite.

Qpy Younger piedmont sediment (Holocene) – Pebbly sand. Brown (7.5YR

5/3) and bioturbated. Very fine petrocalcic nodules locally common but typically

sparse. Pebbles are composed of rhyolite and commonly matrix-supported. Soil

developed below the modern surface exhibits peds that are moderately

53

developed, very fine to fine, subangular blocky to angular blocky, and soft to

moderately hard. Surface is non- to poorly varnished. 1-5(?) m thick.

Qpyr Younger piedmont and recent sediment, undivided (Holocene) – Unit

Qpy and subordinate Qar occupying the floors of drainages near the Sierras

Medianos. Surface is non- to poorly varnished. 1-5(?) m thick.

Qpo2 Younger subunit of older piedmont sediment (middle to upper

Pleistocene) – Clayey-silty, very fine- to medium-grained sand that is

subangular to rounded, poorly sorted, and lithic-rich; contains very sparse coarse

to very coarse sand grains and pebbles. This finer sediment is interbedded with

pebbly beds that are moderately imbricated and bioturbated. Channel-fill sand is

brown (7.5YR 5/3) and contains very fine to fine pebbles, with minor (<15%)

medium to very coarse pebbles. Massive. Near the surface the sediment is

overprinted by a weak to strong calcic horizon (stage I to III) that is moderately

indurated and soft to moderately hard; color of light brown (7.5YR 6/4).

Overlying the calcic horizon is illuviated clay horizon(s). The illuviated clay is

seen in pores and root casts as well as gravel sheens (very faint to faint and

covering 5-25% of the gravel surface). Top soil is characterized by weak, fine to

medium, subangular blocky peds that are soft to moderately hard. Surface

contains more fine-grained sediment than that associated with Qpo1 (commonly

20-60% gravel on the surface) and exhibits a browner color on aerial imageryy;

clast size does not change significantly between Qpo2 and Qpo1. Qpo2 is

commonly inset into Qpo1, although this relation is not ubiquitous. Based on

inset relations, Qpo2 is older than Qao2 and younger than or concomitant with

Qao1. Up to 2 m thick.

54

Qpo1 Older subunit of older piedmont sediment (middle Pleistocene) – Sandy

gravel. Gravel consists mainly of pebbles with minor (<10%) cobbles and very

sparse (<1%) boulders. Locally cross-bedded. Gravel are imbricated and

moderately to poorly sorted. Gravel clasts may have FeO stains and be strong

brown (7.5YR 5/6). Sand is reddish brown (5YR 5/4), slightly silty, fine- to very

coarse-grained sand (mostly medium- to very coarse-grained). Sand is angular to

subangular and poorly sorted. Wavy, erosional base. Top soil is marked by

mixed illuviated clay-calcic horizon(s) overlying calcic horizon(s) exhibiting

stage III carbonate morphology. The Btk horizon is yellowish red (5YR 5/6); faint

clay films and bridges occupy 5-50% of the surface area of a ped, sand grains, or

clasts (as well as coating pores). The Bk horizon is pale yellowish pink to pinkish

white (7.5YR 8.5-9/2; 5YR 8/2) to light reddish brown (5YR 6/4). The calcium

carbonate is pervasive, massive, and moderately indurated (hard to very hard).

Surface gravel typically have partial, thick coats of calcium carbonate. ). There

appears to be more calcium carbonate in this soil than the one associated with

Qao2. Surface is more gravelly than that associated with Qpo2 (60-90% pebbles)

and exhibits a lighter color on aerial imagery. Based on inset relations, Qpo1 is

older than Qao1. Up to 2 m thick.

Basin-fill

QTpp Palomas Formation, piedmont facies (lower Pliocene to lower

Pleistocene) – Sandy gravel channel-fills interbedded with extra-channel

deposits composed of clayey sand with minor, scattered pebbles. Extra-channel

sediment is about subequal (+/-15%) to the coarse channel-fills, but dominates

along lower Alamosa Creek (east of Interstate 25) and in the southeastern

quadrangle corner (corresponding to the distal piedmont subfacies of Lozinsky,

55

1985). Upper 10-30 m of the Palomas Formation is typically dominated by gravel.

Distinguished from younger terrace deposits by less distinct bedding and the

presence of 5-20% clay chips (up to 1 mm long) and clay films on sand grains and

clasts (argillans), with local clay bridging (very faint to distinct and 25-50%

surface coverage). The sandy gravel tends to be in 1-5 m thick, amalgamated

complexes displaying very thin to very thick (mostly very thin to medium),

tabular to lenticular beds; local (~10%) planar- to trough-cross stratification (very

thinly to thinly bedded) where foresets are up to 60 cm thick. Gravel is generally

clast-supported, subrounded (mostly) to subangular, poorly to moderately

sorted, and composed of felsic volcanic clasts (rhyolite and rhyolitc tuffs, mainly

crystal poor with 1-2% of gravel being moderately crystal-rich) and minor (5-

15%), dark gray (mostly) to brown andesite clasts (with phenocrysts of

plagioclase ± pyroxene). Gravel consists primarily of well-graded pebbles, minor

to subordinate cobbles, and 1-10% boulders. Clast imbrication indicates an east-

southeast flow direction. Channel-fills also include minor pebbly sand in beds

that are medium to thick and tabular to lenticular (internally laminated or in

thin, tabular beds), with local cross-stratification up to 30 cm thick. Channel-fill

sand is relatively minor (<25%) and reddish brown to light reddish brown (2.5YR

4/4; 5YR 5-6/4) to yellowish red (5YR 5/6) to reddish yellow (5YR 6/6) to brown

(7.5YR 5/4; 10YR 5/3)), very fine- to very coarse-grained (mostly fine to very

coarse-grained), subrounded to subangular (mostly subrounded), moderately to

poorly sorted, and a volcanic litharenite with 1-5% plagioclase grains. Extra-

channel sediment is massive and dominated by very fine- to lower-medium sand

and clayey-silty fine sand, with minor medium-upper to very coarse sand and

pebbles that are scattered; minor very thin to thick, pebbly channel-fills; and

minor silt beds near the eastern quadrangle border. Clay-rich sediment is light

reddish brown to reddish brown (5YR 5-6/3-4); sandy sediment is light brown

56

(7.5YR 6/3-4). The very fine- to fine-grained sand is mostly subangular (minor

subrounded) and moderately sorted. 0.5% medium, tabular beds of clay-

dominated sediment (reddish brown; 5YR 5/4) showing ped development and

illuvated clay but lacking underlying calcic horizons. Ped development is strong,

coarse, and angular blocky; illuviated clay is manifested by distinct clay films

covering 25-50% of ped faces. Up to 5% accumulation of calcium carbonate (as

nodules or along fractures). Weakly to well consolidated and non- to weakly

cemented by clays (which also facilitate consolidation); the extra-channel

sediment is commonly well consolidated. Lozinsky and Hawley (1986) formally

defined the Palomas Formation and additional detailed descriptions of the unit is

found in this work and Lozinsky (1985). The term "Palomas" was first applied to

outcrops of upper Santa Fe Group basin fill by Gordon and Graton (1907),

Gordon (1910), and Harley (1934); Lozinsky and Hawley (1986) provide more

information regarding the usage of the term since these early works. Fossil data

(summarized by Morgan and Lucas, 2012), basalt radiometric dates (Bachman

and Mehnert, 1978; Seager et al., 1984), together with magnetostratigraphic data

(Repenning and May, 1986; Mack et al., 1993; 1998; Leeder et al., 1996; Seager and

Mack, 2003), indicate an age range of 4.5-0.78 Ma for the Palomas Formation.

Surface soil is marked by a petrocalcic horizon that is 1-2 m thick and generally

exhibits a stage IV carbonate morphology. Lower part of the petrocalcic horizon

is gradational. More information on this petrocalcic horizon and the

constructional surface developed on the Palomas Formation, the Cuchillo

surface, can be found in McCraw and Love (2012). The degree of clast varnishing

on the Cuchillo surface is variable, depending on the degree of reworking by

sheetflooding; near the south-central quadrangle border the clasts are strongly

varnished. 100-131 m thick according to Lozinsky and Hawley (1986).

57

QTpa Palomas Formation, axial facies (lower Pliocene to lower

Pleistocene) – Thick intervals (>= 10 m) of amalgamated channel-fill sands

interbedded with floodplain sediment of similar thicknesses. The channel-fill

sands include minor, lenticular, pebbly beds up to 2 m thick; these pebbly

channel-fills contain very thin to thin, planar foresets up to 1 m thick. Channel-

fill sands are massive or in medium to thick, tabular beds that are internally

laminated. Lozinsky (1985) reports that the sand is generally arkosic and pebbles

consist of quartz, chert, granite, sandstone, and a variety of volcanic rock types.

Floodplain sediment is light reddish brown (5YR 6/3) and consists of clay-silt in

medium to thick, tabular beds. Some zones in the floodplain facies have

abundant calcium carbonate nodules (up to 5 mm thick), some of which appear

to be associated with paleo-burrows. This unit grades laterally westward into

unit QTpp. Fossils collected from this general stratigraphic interval suggest a

3.0-3.3 Ma age (Morgan and Lucas, 2012, Elephant Butte Lake fauna) or 3.0-5.0

Ma (if we extend this unit into the subsurface). The 5.0 Ma maximum age

constraint is constrained by magnetostratigraphic data (Mack et al., 1993; 1998;

Leeder et al., 1996; Seager and Mack, 2003). >12 m thick.

Volcanic bedrock

Tvp Vicks Peak Tuff (upper Oligocene) – Light to medium gray (5YR-7.5YR

7/2), fine-grained (3-10% visible crystals) ignimbrite exhibiting flattened pumice

(fiamme; 10-15%). Crystals include sanidine and <1% quartz. ~5%

ferromagnesium minerals. 40Ar/39Ar dating indicates an age of 28.75 ± 0.04 Ma

(former age of 28.56 Ma of McIntosh et al., 1991, corrected using the revised Fish

Canyon sanidine age of 28.02 Ma from Renne et al., 1998). At least 60 m thick.

58

Tvpb Brecciated Vicks Peak Tuff (upper Oligocene) – A crystal poor tuff

interpreted as Vicks Peak Tuff (see Tvp description above) but brecciated. At

least 60 m thick.

Ta Andesite (upper Oligocene) – Gray andesite. 25-40% visible crystals in

hand sample, with phenocryst assemblage consisting of plagioclase and

subordinate pyroxene or amphibole. Locally exhibits vesicular textures.

Underlies the Vicks Peak Tuff. Generally identified using float. >15 m thick.

SUBSURFACE UNITS

Tsf Santa Fe Group below the Palomas Formation (upper Oligocene to

Miocene) – Coarse channel-fills interbedded with tan-brown mudstones and

clayey-silty, very fine- to fine-grained sandstones. The coarse channel-fills are

composed of gravel and sandstone. The gravel consist of pebbles with minor

cobbles. Clasts and coarse sand grains are subrounded-subangular and

composed largely of light gray to pinkish, felsic clasts (rhyolite and ash-flow

tuffs) with minor dark-brown andesite. Consolidated and variably cemented.

Tilted 2-4° E (apparent dip) and overlies older strata across an angular

unconformity apparently dipping 5° E (see cross section A-A'). East of the Mud

Springs fault in cross-section A-A', this unit is subdivided according to gross

texture. Greater than 1880 m thick on the hanging wall of the Mud Springs fault.

Tvs Volcaniclastic sediment interbedded with volcanic flows (upper Eocene

to upper Oligocene) – Includes volcaniclastic sandstone and conglomerate

eroded from surrounding volcanic highlands. Likely interbedded with andesite

to rhyolite volcanic flows that increase in abundance to the west. Correlative to

59

the Datil and Spears Groups as well as the Thurman Formation. Thickness is

poorly constrained but speculated to be 600 m on the hanging wall of the Mud

Springs fault. Unit was eroded off of the footwall of the Mud Springs fault prior

to deposition of Tsf.

Kmc McRae Formation (Upper Cretaceous) – Lower 120 m consists of dark

brown to olive-green sandstone interbedded with volcaniclastic conglomerates

and olive-green to purple shales. Upper part is composed of maroon to brown

shales interbedded with sandstone and minor conglomerate. Preserved thickness

on the quadrangle is 530 m (description from Lozinsky, 1985).

Ku Undivided Cretaceous rocks (Upper Cretaceous) – Includes the following

formations, listed in ascending order: 1) the Dakota Sandstone (24-75 m thick), 2)

Mancos Shale divided by the Tres Hermanos Formation (sandstone and

mudstone) -- together this is package is ~80 m thick), and 3) Crevasse Canyon

Formation (1005-1010 m thick). The latter consists of tan-brown, sandstone

channel-fills interbedded with olive-green to brown shale, mudstone, and

siltstone. The upper 34 m of the Crevasse Canyon Formation is dominated by

sandstone and pebble conglomerate whose clasts are composed of quartz and

chert [description from Lozinsky, 1985, with nomenclature following Seager and

Mack, 2003]. 400 m thick in the Gartland 1 Brister exploratory well, corrected for

dip, which means that much of the Crevasse Canyon Formation was eroded

prior to McRae deposition.

Psa San Andres Formation (Upper Permian) – Gray limestone with minor

interbeds of shale and sandstone. Rare chert nodules and lenses. 210-230 m thick

[description from Lozinsky, 1985].

60

Py Yeso Formation (Lower Permian) – Sandstone and siltstone exhibiting

yellowish, orange, greenish, and reddish to reddish brown colors. Abundant

gray limestone in middle and upper parts. Local beds of gypsum and

gypsiferous siltstone found in upper part [ description from Jahns et al., 1978,

and Lozinsky, 1985]. 270-280 m thick, corrected for dip. The unit thickens to the

east and is as much as 533 m thick in the vicinity of the Gartland 1 Brister

exploration well; this thickening is attributed to dioritic(?) sills and other

intrusives (Lozinsky, 1987).

Pba Abo and Bursum Formations (Lower Permian) – The Bursum Formation

is composed of reddish-purple siliclastic beds interbedded with limestone. The

siliciclastic sediment consists largely of shale-siltstone but includes minor

sandstone (~79 m thick according to Lucas et al., 2012). The Bursum Formation is

conformably overlain by the Abo Formation (~150 m thick according to Maxwell

and Oakman, 1990). The latter is composed of dark red shale and sandstone;

there is minor orange-red arkosic sandstone and conglomerate as well as

purplish-gray, nodular calcareous mudstone (Maxwell and Oakman, 1990). Well

data on cross section A-A'indicate a thickness of 250-260 m, corrected for dip.

IPrnb Red House, Nakaye, and Bar B Formations (Pennsylvanian) – Largely

grayish, cherty limestone interbedded with shale; very minor sandstone and

pebble conglomerate. 540-550 m thick according to Lucas et al., 2012 (who used

the names Red House, Gray Mesa, and Atrasado Formations).

Pz Lower to middle Paleozoic, undivided (Cambrian through Devonian) –

Sedimentary strata that includes the Bliss Sandstone at the base (Upper

Cambrian-Lower Ordovician and 40-55 m thick). Overlying the Bliss Sandstone

61

is a thick sequence dominated by limestones and dolomites, including (from

bottom to top): 1) the El Paso Group (Lower Ordovician) represented by the Hitt

Canyon Formation (~120 m thick) and overlying McKelligon Limestone (~36 m

thick) -- nomenclature following Hayes, 1975a,b), and 2) the Montoya Formation

(Upper Ordovician and ~110 m thick). Overlying these carbonate-dominated

strata is a shaly-siltstone-domianted interval that includes the Percha Shale, Sly

Gap, and Oñate Formations (Devonian and 30-40 m thick) -- which Lucas et al.

(2012) advocates lumping into the Percha Formation. Devonian strata are missing

in the northern Mud Spring Mountains (Maxwell and Oakman, 1990) and may

not be present in cross-section A-A'. Total thickness of 375-380 m in the Mud

Spring Hills (Lucas et al., 2012), but we used a thickness of ~230 m based on

thicknesses from the West Elephant Butte Federal No. 1 well.

XYu Proterozoic, undivided (Paleo- to Neoproterozoic) – Reddish gray

quartzite, dark gray and brown quartz schist, quartz-biotite schist, foliated

amphibolite, and porphyritic, reddish granitic gneiss. Possible metarhyolite and

granite. Rocks are complexly interlayered and contorted [Maxwell and Oakman,

1990; Jahns et al., 1978; Nelson et al., 2012).

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