Agricultural Experiment StationCollege of Agriculture

B-1069December, 1998

Soils of WyomingA Digital Statewide Map at1:500,000-Scale

Larry C. MunnDepartment of Renewable Resources, College of Agriculture,University of Wyoming, Laramie, Wyoming

Christopher S. ArnesonSpatial Data and Visualization Center, University of Wyoming,Laramie, Wyoming

Editor: Tonya Talbert

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation withthe U.S. Department of Agriculture, Glen Whipple, Director, Cooperative Extension Service, University ofWyoming, Laramie, WY 82071.

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This report is preliminary and has not been reviewed for technical accuracy. Any use of trade, product, orfirm names is for descriptive purposes only and does not imply endorsement by the Agricultural ExperimentStation, the University of Wyoming, or the Spatial Data and Visualization Center. Although these data havebeen used by the SDVC and have been successfully imported into database and GIS programs, no warranty,expressed or implied, is made by UW as to how successfully or accurately the data can be imported into anyspecific application software running on any specific hardware platform. The fact of distribution shall notconstitute any such warranty, and no responsibility is assumed by the AES, SDVC, or the UW College ofAgriculture in connection therewith.

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Background

The following is the recommended bibliographic citation for this publication:

Munn, L.C. and C.S. Arneson, 1998. Soils of Wyoming: A Digital Statewide Map at 1:500,000-Scale. Agricultural Experiment Station Report B-1069. University of Wyoming, College of Agri-culture, Laramie, Wyoming.

The Soils Map of Wyoming is intended todepict process-based soil categories found inWyoming. Representative soils in the map-ping units for this map are classified at thefamily level of Soil Taxonomy (Soil SurveyStaff 1975; Soil Survey Staff 1998). Technicalsoil terminology follows definitions in theGlossary of Soil Science Terms (Soil Science So-ciety of America 1997). The map was prima-rily generated for a statewide study ofground-water vulnerability to contaminationfrom pesticides. In that context, it was to beused to assist in the generation of an esti-mated surficial aquifer recharge map and toserve as one of the individually rated layersrequired within a DRASTIC-based (Aller etal. 1987) aquifer sensitivity analysis(Hamerlinck and Arneson 1998).

This map provides a generalized descriptionof soils within the state of Wyoming. Soilsare highly variable, both on a regional basis(plains, mountains, basins) and locally, withchanges in topography (northern versussouthern slopes, side slopes versus ridge crestor foot slope positions), vegetation, climate,and geology. This map should be used forbroad scale planning and general assessmentof large areas of land. It should not be usedfor site specific interpretations such as site se-lection for an underground fuel storage tankor the development of management plans forindividual farm fields. Such site intensive

land uses require much more detailed soilsinformation than is provided by this map.

The Soils Map of Wyoming and the general-ized soils maps of the Wyoming counties arederived based on the five soil forming factormodel first proposed in its entirety by theRussian soil scientist Doukachev in the1880s. This model was introduced broadly toAmerican soil scientists by Hans Jenny(Jenny 1941). The five factors of soil forma-tion are soil parent material, climate, biota,topography, and time. As Hudson (1992)pointed out, soil surveying is an activity thatconforms well to the theories of paradigm-based science. During detailed soil surveys,field mapping is based on the projection ofsoil map unit concepts onto the landscape,after which map unit composition andboundary placement are subject to immediatefield checking in the form of soil pitexcavation(s). Generalized soils maps are of-ten based on either a process of consolidationof detailed soils maps, or on projection oflimited data from direct observation across abroad area through use of soil-landscapemodels. In the United States, the model usedto describe soil-landscape relationships ismost commonly the soil forming factormodel. The maps for this project were pre-pared using current understanding of soil-landscape models and available data in theform of published soil surveys, maps, and re-

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ports of the Natural Resource ConservationService (NRCS), the Forest Service (FS), theBureau of Land Management (BLM), andnumerous theses and scientific papers pub-lished by the Wyoming Agricultural Experi-ment Station and the University of Wyo-ming.

The soil map presented here differs from theSTATSGO map developed by the NRCS(National Cartographic and GIS Center1998) in several ways. The STATSGO mapswere developed by generalizing existing de-tailed soil surveys and were prepared on a1:250,000-scale topographic map base. Themapping units in the STATSGO map con-tain from 1 to 21 components, and the soilscomponents are represented at the serieslevel. The STATSGO map provides a some-what more detailed description of the soils inthe state, with consequent complexity in in-terpretations. The detailed maps from whichthe STATSGO map was generalized wereproduced by numerous scientists over a 30-year time span. The surficial geology map ofthe state and the state bedrock geology mapwere not available in electronic format whenthese maps were produced and the originalmapping was done on aerial photographs.

The scale of 1:500,000 used for this map wasspecified by the larger Wyoming Ground-Water Vulnerability Mapping Project(Hamerlinck and Arneson 1998). The mapsare based on a simplification of the five soilforming factor model. Climate is proxied byelevation. This was derived from the 3-arc-second USGS Digital Elevation Model(DEM) for the state. There is a strong corre-spondence between elevation and precipita-tion in the state, and temperature regimescan generally be characterized by elevation.

Vegetation is also closely tied to elevationthrough its effect on precipitation and tem-perature. Three temperature regimes aremapped in Wyoming: cryic in the highermountains; frigid in the foothills, the highplains along the Rocky Mountain front, lowmountains, and high intermountain basins;and mesic in lower elevation basins and theGreat Plains (See Appendix for definitions oftemperature regimes). There are small areas ofa fourth temperature regime (pergelic) at el-evations above 10,000 feet in the state’s high-est mountains. Soil parent material is derivedfrom the digital version of the state geologymap (Green and Drouillard 1994) and thestate surficial geology map by Case, Arneson,and Hallberg (1998). Vegetation is inferredfrom climate, slope, and parent material.Time, or soil age, is inferred from elevationand surficial geology. The topographic factoris inferred from elevation, surficial geologyand bedrock geology. The analysis of theselayers was conducted using ARC/INFO Geo-graphic Information System software on aSilicon Graphics UNIX workstation.

The boundary between cryic and frigid tem-perature regimes is at approximately 7,800feet elevation in the southern half and at7,500 feet in the northern half of the state.The boundary between mesic and frigid tem-perature regimes ranges between 5,000 feet inthe northern part of the state and 6,500 feetin the southern part. Small areas of pergelictemperature regime exist above 10,000 feet inthe highest mountains (Beartooths,Absarokas, Tetons, Bighorns, Wind Rivers,Snowy Range, Sierra Madre). Age relation-ships of mountainous surfaces are controlledby slope gradient and glacial history. Slopeswith steep gradient (greater than 25%) arecommonly occupied by Entisols

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(Cryorthents) and Inceptisols (Dystrocryepts).Glacial deposits of Pinedale age usually areoccupied by Inceptisols under forest(Dystrocryepts) and Mollisols under grass-lands (Haplocryolls). Soils will be HumicDystrocryeptss above 9,500 feet under alpineturf. Soils in riparian areas in the mountainsare typically Entisols (Cryofluvents) orInceptisols (Cryaquepts) with small areas oforganic soils (Histisols). Glacial deposits ofBull Lake age or older are commonly occu-pied by Alfisols (Haplocryalfs) under con-tinuous forest or Mollisols (Haplocryolls) un-der grassland. Non-glaciated surfaces withgradients less than 15% are usuallyHaplocryalfs under forest or Haplocryolls un-der grass.

In foothills and lower mountains, steepsouth-facing slopes are commonly occupiedby Entisols (Torriorthents) and Inceptisols(Ustochrepts). Hillslopes under sagebrushand grasses are frequently Mollisols, mostcommonly without argillic (clay accumula-tion) horizons. Where grassland is inter-mingled with forest, the grassland sites areoften on either warmer aspects or finer tex-tured (less rocky) soils. Mountain mahogany(Cercocarpus montanus) is a reliable indicatorof high coarse fragment contents and of adeep rooting environment, albeit in fracturedbedrock or skeletal materials.

In foothill settings, Idaho fescue (Festucaidahoensis) and Ponderosa pine (Pinus ponde-rosa) are generally indicators of the break be-tween frigid and cryic temperature regimes.Cacti grow at high elevations on dry slopesand indicate that the aridic moisture regimeextends into areas with cryic soil temperatureregime. Aspect effects are strong in this eleva-tion zone, and it is not uncommon to have

cool Alfisols (Haplocryalfs) on north facingcanyon walls matched by noticeably warmer(frigid), dry Entisols (Torriorthents) on southfacing canyon walls.

In Wyoming, high basins present a mixtureof old, tilted sedimentary rock, which is Cre-taceous in age or older, along with youngerTertiary, Pleistocene, and Holocene sedi-ments. Often, the Cretaceous and older rockwill occur in bands along basin margins withyounger sediments showing varying degreesof incision by erosion in basin centers. Aquick view of a topographic map will usuallyprovide ready separation of these two zones.Because basins are drier than mountains, veg-etation cover may be limited on some slopesin the basins (many of the south aspects)where plant cover is too sparse to preventerosion. Associations of soils include Entisols(Torriorthents) on slopes of 15% or moreand on south and west facing slopes, whileon low-relief surfaces the soils will beAridisols, usually either Haplocalcids,Haplocambids, or Haplargids on most Creta-ceous-age parent materials. On Tertiary par-ent materials high in clay, the soils may be acomplex of Aridisols, some of which arestrongly affected by sodium (Haplargids andNatrargids). On stabilized sand dunes, thesoils are Entisols (Torripsamments). On pla-yas with clayey textures and clay dunes fre-quently associated with them, soils are com-monly salt-affected Aridisols (Calcigypsids orGypsisalids). Soils along ephemeral channelsare usually Entisols (Torrifluvents) on sur-faces younger than approximately 6,000 yearsold, with wet Mollisols (Haplaquolls) occur-ring along streams with permanent high wa-ter tables. Early Holocene surfaces are com-monly occupied by moderately developedInceptisols (Haplocambids or Haplocalcids),

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depending upon soil texture and source ofcarbonates. Many high basins of Wyominghad permafrost environments during the LatePleistocene, and these old surfaces are oftencovered with low-relief mounds. The soils aretypically Aridisols with clay enriched subsoils(Haplargids) on intermound areas andAridisols with only moderate development(Haplocambids) on mound areas.

Along the eastern edge of the Rocky Moun-tains there is a band of mounded topographysimilar in origin to mounds in the high ba-sins. These mounds are commonly occupiedby Mollisols with very thick organic matterenriched surface layers (A horizons) (pachicsubgroups), while the intermound areas areoccupied by similar soils but with thinnersurface horizons (typic subgroups). Riparianareas are occupied by wet Mollisols(Haplaquolls) and Entisols (Fluvents). Fur-ther from the mountain front, soils aresandy-textured Entisols (Torripsamments) onold dunes, shallow to moderately deepEntisols (Torriorthents) on Tertiary materialsthat are either very sandy or very clayey intexture, and a mixture of Entisols (Fluvents)and Mollisols (Haplaquolls) along riparianareas. For many landscapes with coarser tex-tured Tertiary materials (e.g., Arikaree forma-tion), ridges and even cliffs and mesas on thelandscape are common; these are supportedby conglomerate layers. The Tertiary WhiteRiver formation is highly erodible and mayinclude badland areas. The Green River Basinin the southwestern corner of the state con-

tains a large exposure of Tertiary sedimentaryrock, which controls landscape topographicfeatures and soils. There are several largedune fields in the state with west to east axes,resulting from wind corridors. Playas occurlocally in both basin and plains landscapes;some are saline and others are periodic, tem-porary freshwater wetlands.

The Black Hills have a typical Laramidemountain structure. However, uplift in theBlack Hills was not as high as for the RockyMountains, and the surface of the range isstill largely mantled by sedimentary rocks ofTertiary and older ages. The range was notglaciated and the soils atop the Black Hillsare a mosaic of Alfisols (Eutraboralfs) andMollisols (Argiustolls).

The Wyoming Range and Overthrust Beltalong the western boundary of the state arethe product of very old mountain buildingevents and present soil parent materials ofimmense geologic complexity. Ridges andvalleys often result from differential resistanceto weathering in folded sedimentary rocks ofTertiary, Cretaceous, and older ages.

Overall, because of the relatively harsh cli-mate in the state, soils in Wyoming show aclose relationship to geologic parent materialsand vegetation communities under whichthey form. Landscape stability and age rela-tionships are also quite important in under-standing soil occurrence throughout thestate.

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Soil Map Unit (SMU) Descriptions: Soils Map of Wyoming

Soil Zone 1: Yellowstone National ParkArea. Mountains and high plateau.Cryic, udic, and aquic.

WY01: Typic Dystrocryepts-TypicHaplocryalfs, loamy-skeletal, mixed; andHistic Cryaquepts, fine-loamy over sandy orsandy-skeletal, mixed. Under continuous co-niferous forest (Lodgepole Pine, EnglemannSpruce, Subalpine Fir, and Douglas Fir), soilson geologic parent materials and surfaces thatare older than Pinedale are typicallyHaplocryalfs. The Yellowstone Plateau areawas heavily glaciated during the Pinedale(Wisconsin) glaciation and most surfaces areof Late Pinedale or Holocene age. On theseyounger parent materials and/or surfaces, thedominant soils are Dystrocryepts. Cryaqueptsoccur in riparian areas. Inclusions may in-clude Typic Cryofluvents along small chan-nels and Cryofibrists in depressions inPinedale moraines and along low-gradientsegments of streams. Typic Haplocryolls andHumic Dystrocryepts may occur in smallopenings in the forest.

WY02: Typic Haplocryolls, fine-loamy; andHistic Cryaquepts, fine-loamy over sandy orsandy-skeletal. Haplocryolls occur in moun-tain meadows, which are predominately onsouth and west facing slopes, and are oftenon finer textured parent materials than sur-rounding forest soils. Cryaquepts occur alongriparian areas.

WY03: Typic Cryorthents and HumicDystrocryepts, loamy-skeletal; and HisticCryaquepts, fine-loamy over sandy or sandy-skeletal. Topography for this unit is irregular,with Humic Dystrocryeptss occurring undergrass or grass with scattered trees on small

benches and low gradient segments of theslope. Cryorthents are on very steep slopesand around the base of rock outcrops.Cryaquepts occur along riparian areas.

Soil Zone 2: Absaroka Volcanics. Moun-tains. Cryic, udic, and aquic.

WY03: Typic Cryorthents and HumicDystrocryepts, loamy-skeletal; and HisticCryaquepts, fine-loamy over sandy or sandyskeletal. Soils are similar to those in SoilZone 1, except the mineralogy reflects volca-nic parent materials.

WY04: Typic Cryorthents, loamy-skeletal;rock outcrop; and Histic Cryaquepts, fine-loamy over sandy or sandy-skeletal. ThinCryorthents and bedrock outcrops dominatethis landscape. In narrow riparian areas be-tween steep slopes, Cryaquepts have devel-oped in accumulations of fine materialsweathered from the surrounding uplands.

WY05: Histic Cryaquepts, fine-loamy oversandy or sandy-skeletal; and HumicDystrocryepts, loamy-skeletal. In alpine set-tings, the soils over most of the landscape arean association of Cryaquepts in riparian areasand Humic Dystrocryepts, with moderatelydeep profiles, on uplands. Umbric epipedonscontain 6 to 8% organic matter and are typi-cally 25 to 50 cm thick.

Soil Zone 3: Middle Rocky Mountains.Cryic, udic, and aquic.

WY06: Typic Haplocryalfs, TypicDystrocryepts, and Typic Haplocryolls,loamy-skeletal; and Histic Cryaquepts, fine-loamy over sandy or sandy-skeletal. On stableslopes which are older than Pinedale (LateWisconsin), the predominate soils are

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Haplocryalfs. Dystrocryepts occur on slopesgreater than 40% and on Pinedale andyounger surfaces (Pinedale tills and holocenesurfaces). Haplocryolls occur under moun-tain meadow vegetation and are most com-mon on south-facing slopes. Cryaquepts arefound along narrow riparian areas.

WY07: Typic Haplocryolls, fine-loamy;Chromic Haplocryerts, fine; and HisticCryaquepts, fine-loamy. These soils occur onMesozoic-age bedrock with the Haplocryertspredominating on marine shales. Dominantvegetation is grass or forest with thin canopycoverage and clusters of aspen in wet areas.Cryaquepts predominate in riparian areas.

WY08: Rock outcrop and LithicCryorthents, loamy-skeletal. These residuallandscapes present a rugged appearance with50 to 60% of the area covered by rock out-crop. The thin Cryorthents occur inter-mingled with the bedrock.

WY42: Typic Hapludolls and TypicHapludalfs, loamy-skeletal, mixed, frigid.These soils occur in the foothills along theflank of the higher mountains and represent atransition from the basins to the highermountains. Hapludolls are common onsouth- and west-facing slopes; Hapludalfspredominate on north-facing slopes and onboth canyon walls of narrow canyons.

Soil Zone 4: Bighorn Basin. Intermoun-tain Basin. Mesic, aridic.

WY09: Typic Haplargids and TypicHaplocalcids, fine-loamy over sandy orsandy-skeletal, mesic; and TypicTorriorthents, fine-loamy and coarse-loamy,mesic. Aridisols occur on colluvial and allu-vial landscapes, while Entisols occur on re-sidual landscapes.

WY10: Typic Torripsamments, mesic. Thesesoils are on stabilized dunes. They show littlehorizon development; thin A horizons are themost apparent change from the parent mate-rial (stabilized dune sand).

WY11: Calcic Haplosalids, fine, mesic. Thesesoils are associated with marine shales and oc-cur in topographic depressions where run-offwater from the surrounding landscape accu-mulates and evaporates concentrating salt.

WY12: Typic Torriorthents, loamy, mesic;and rock outcrop. These soils form in a vari-ety of sedimentary parent materials which areexposed along the perimeter of the basin.Soils are shallow or moderately deep to softbedrock.

WY13: Typic Torriorthents, fine, mesic; androck outcrop. These soils form over fine-tex-tured Cretaceous bedrock. Outcrops of shaleoccur as small badlands; outcrops of coarsertextured rock support long, narrow ridgeswith finer textured soils along the flanks.

WY14: Typic Haplargids and TypicNatrargids, fine-loamy or coarse-loamy,mesic. These soils occur on low-gradient col-luvial slopes (less than 15%) and reflect thetexture of the underlying bedrock as well asthe effects of slope processes.

WY15: Typic Torrifluvents, sandy-skeletal,mesic; and Typic Haplocambids, fine-loamyover sandy or sandy-skeletal, mesic. Thesesoils occur on Holocene-age terraces andslopes along small streams. The Torrifluventsoccupy the first and second terraces above themodern channel.

Soil Zone 5: Powder River Basin.Northern Great Plains. Mesic, aridic.

WY16: Ustic Haplargids, Ustic Haplocalcids,

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and Aridic Haplustolls, fine-loamy, mesic;and Torriorthents, loamy-skeletal, mesic.These soils have formed from a variety ofparent materials on Pleistocene and Holocenesurfaces, weathered from Tertiary and otherbedrocks. The Haplargids and Haplocalcidsoccur across broad expanses of the landscape.The Torriorthents occur along eroded drain-age ways and around rock outcrops. TheHaplustolls occur where snow accumulationsignificantly enhances soil water.

WY17: Typic Torriorthents, loamy-skeletal,mesic; and rock outcrop. These stony soilsoccupy ridge crests where coal bed fires havecreated clinker. The soils tend to be muchcoarser than the soils on the adjacent lowerslopes and contain hard clasts.

WY18: Typic Torriorthents and EnticHaplustolls, fine-loamy, mesic. These soilsoccur on reconstructed landscapes that havebeen disturbed by mining. The occurrence ofmollic epipedons is a function of reclamationpractices and is not necessarily tied to topog-raphy or potential productivity.

WY19: Typic Haplogypsids, fine, mesic.These soils occur in clayey playas where gyp-sum has accumulated in sufficient quantity toqualify as a gypsic horizon.

WY42: Typic Hapludolls and TypicHapludalfs, loamy-skeletal, mixed, frigid.These soils are similar to those in Soil Zone3. They occur in foothills along the marginof the Powder River Basin.

Soil Zone 6: Black Hills. Mountains.Frigid, udic, and ustic.

WY20: Typic Hapludalfs and TypicArgiudolls, fine-loamy; and TypicHaplaquolls, fine, frigid. The Hapludalfs sup-port open to dense stands of Ponderosa Pine.

The Argiudolls occur under moist meadows,while the Haplaquolls occur along narrowriparian areas.

WY21: Ustic Haplocambids and UsticTorriorthents, fine, frigid; and rock outcrop.These clayey soils are derived from acid shalesand show little profile development. TheHaplocambids occur on low-gradient sur-faces. Torriorthents occur intermingled withareas of shale outcrop in badlands-type to-pography.

WY22: Typic Argiudolls and TypicHaplaquolls, fine-loamy, frigid. These soilsoccur in moist meadows along riparian areasin the mountains. The Haplaquolls have ac-cumulated greater amounts of organic matterdue to their high water table.

WY43: Ustic Haplargids and UsticHaplocambids, fine and fine-loamy, mesic.These soils have weathered from interbeddedsandstones, siltstones, and shales. TheHaplargids are on low-gradient slopes (lessthan 15%); the Haplocambids are on steeperslopes.

Soil Zone 7: Southeast Wyoming.Northern Great Plains. Frigid andmesic, aridic.

WY10: Typic Torripsamments as in Zone 4,except soil temperature regime is frigid.

WY23: Typic Argiustolls, fine-loamy; andTypic Argiustolls, fine-loamy over sandy orsandy-skeletal, mixed, frigid. These soils oc-cur on Tertiary and Pleistocene parent mate-rials (mostly alluvial fan deposits of Tertiaryage, or local alluvium of Pleistocene age.)

WY24: Ustic Haplocambids and UsticTorriorthents, fine, frigid. These moderatelyand weakly developed soils occur on gentle to

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steep slopes over the Tertiary White Riverformation. Profile development is shallow ormoderately deep.

WY25: Ustic Torriorthents and AridicUstochrepts, loamy-skeletal, frigid. Thesesoils occur along the front of the LaramieRange and the Hartville uplift. TheUstochrepts support scattered stands of Pon-derosa Pine. Soils are shallow or moderatelydeep and coarse textured.

WY26: Ustic Torriorthents and UsticHaplocambids, fine, frigid. These soils havedeveloped on Cretaceous-age bedrock (shale)and are moderately deep or shallow. TheHaplocambids are on low-gradient fans andslopes; Torriorthents occur on steeper slopes(greater than 15%).

WY27: Typic Torrifluvents and Typic Hapla-quolls, fine-loamy over sandy or sandy-skeletal,mixed, frigid. These soils occur along riparianareas with the Torrifluvents developing alongchannels scoured by flooding and the Hapli-quolls developing on low-gradient channel sec-tions where vegetation is well established andhigh water tables occur during most of the year.

WY44: Ustic Haplargids and Ustic Torri-fluvents, fine-loamy over sandy or sandy-skel-etal, mixed, mesic. These soils occur on allu-vium and slopes of Pleistocene and Holoceneage over a variety of bedrocks. The Torri-fluvents occur on the active floodplain;Haplargids occur on more stable landscapesegments.

Soil Zone 8: Medicine Bow andLaramie Mountains. Mountains. Cryic,udic, and aquic.

WY28: Typic Haplocryalfs and TypicDystrocryepts, loamy-skeletal, mixed; andTypic Haplocryolls, fine-loamy, mixed.

Haplocryalfs occur under forest on till parentmaterials older than Pinedale (140,000 yearsold and older) and on non-glaciated landforms where the slope gradient is less than ap-proximately 10%. Dystrocryepts occur underforest on till of Pinedale age and on slopes(>10%) that were unstable during the Pinedaleglaciation. Haplocryolls occur under grassesand shrubs on west and south aspects and indry parks on Tertiary-age parent materials.

WY29: Histic Cryaquepts and TypicCryaquolls, fine-loamy over sandy or sandy-skeletal, mixed. These are poorly drained soilsalong riparian areas. Only A horizon thick-ness is different between the two soils(thicker in the Mollisols). Depth to watertable in the profile varies from 0 to 50 cmover the course of the summer.

WY30: Typic Dystrocryepts and LithicCryorthents, loamy skeletal, mixed; and rockoutcrop. These soils are found at high eleva-tions and on very resistant parent materials.They are on eroding slopes or the youngesttills in the region (Neoglacial).

WY31: Typic Dystrocryepts and TypicCryorthents, loamy skeletal, mixed. This unitoccurs on Triassic, Permian, and Cretaceoussedimentary rock along the flanks of themountain range. The soils are moderatelydeep or shallow.

WY32: Typic Dystrocryepts, loamy-skeletal,mixed; and rock outcrop. These soils occuron Precambrian granitic parent materials.The Inceptisols are mostly moderately deepwith less than 12% clay in their thin B hori-zons (Bw). The rock outcrops take the formof rounded boulders and sheets of rock.

WY45: Typic Hapludalfs and AridicHaplustepts, loamy-skeletal, mixed, frigid.

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These soils occur along the base of the moun-tain ranges in the region and support openstands of Ponderosa Pine as well as other co-nifers. The Hapludalfs are on low-reliefslopes and nearly level surfaces. TheHaplustrepts are on slopes greater than 15%and on the narrow valley floors of canyons.

Soil Zone 9: Laramie and Wind RiverBasins. Intermountain Basins. Frigid,aridic.

WY09: Ustic Haplargids and UsticHaplocalcids, fine-loamy over sandy orsandy-skeletal, frigid; and Ustic Torrior-thents, fine-loamy and coarse-loamy, frigid.In this region, the soils in this unit havefrigid temperature regimes. These soils occuron old alluvial terraces along major rivers.Soils younger than mid-Pleistocene age are anassociation of Haplargids and Haplocalcids.On older landscapes, Haplocalcids predomi-nate. Torriorthents occur along south-facingterrace scarps; textural family is determinedby underlying bedrock.

WY10: Typic Torripsamments, frigid. Thesesoils on stabilized dunes show little profiledevelopment but are quite productive undernative rangeland.

WY33: Lithic Torriorthents, loamy-skeletal,frigid; and rock outcrop. These soils occuralong both sides of bedrock outcrops thatform ridges along the flanks of the basins.The rock outcrop is usually sandstone orlimestone.

WY34: Ustic Haplargids and Ustic Natr-argids, fine-loamy, frigid. These soils occur asan association on residual landscapes and inlocal colluvium derived from Tertiary-age par-ent materials. Natrargids show less productiv-ity under sagebrush and grass than Haplargids.

WY35: Typic Natrargids and TypicTorriorthents, fine, frigid. These soils occuron landscapes underlain by Triassic and Cre-taceous bedrock (shales). The Torriorthentsoccur in a badlands type topography, whilethe Natrargids occur on small, local alluvialfans at the foot of badland scarps, and onlow-gradient slopes.

WY36: Ustic Torriorthents and Ustic Haplo-calcids, coarse-loamy, frigid. These soils occur oncalcareous sandstone of Permian age (redbeds).Haplocalcids occur on low gradient slopes;Torriorthents on slopes greater than 10%.

WY37: Typic Petrocalcids and Ustic Calci-argids, fine-loamy over sandy or sandy-skeletal,frigid. These soils occur on the highest terracesalong major streams where the surfaces are mid-Pleistocene age or older. On some surfaces, thepetrocalcic horizon of the Palecalcids is nearlycontinuous; on other surfaces, Palecalcids andHaplocalcids occur as a complex.

WY38: Ustic Haplocambids and UsticHaplargids, coarse-loamy, frigid. These soilsoccur as a complex on late-Pleistocene ageterraces along major streams, and on slopes ofless than 15% gradient of the same age.

WY44: Ustic Haplargids and TypicTorrifluvents, fine-loamy over sandy orsandy-skeletal, mixed, mesic. These soils oc-cur below 5,000 feet in elevation in a rela-tively small area in the Wind River Basin.The Haplargids occur on alluvial terraces; theTorriorthents occur along the scarp slopes.

Soil Zone 10: Green River Basin. Inter-mountain Basin. Frigid, aridic.

WY06: Typic Haplocryalfs, TypicDystrocryepts, and Typic Haplocryolls,loamy-skeletal, mixed; and Histic Crya-quepts, fine-loamy over sandy or sandy-skel-

10

etal, mixed. These soils are similar to those inthe same unit in Soil Zone 3. They are con-fined to the highest elevations of this region.

WY10: Typic Torripsamments, frigid. Thesesoils are very similar to Torripsamments inother areas of the state, except they are inter-mingled with active dunes.

WY11: Typic Haplosalids, fine, frigid. TheseHaplosalids occur in saline playas and aresimilar to those of this unit in Zone 4, exceptthey are frigid.

WY17: Rock outcrop and Typic Torrior-thents, loamy-skeletal, mixed, frigid. Thesesoils are similar to those in Zone 5, exceptthe coarse fraction of the soil consists of clastsof the local bedrock, rather than clinker.

WY39: Ustic Haplargids, UsticHaplocambids, and Ustic Natrargids, fine-loamy, mixed, frigid. On Tertiary parent ma-terials along the flank of the Wyoming Range

uplift, the soils are found in an associationreflecting slope position and parent materialsodium content. The Haplargids occur onstable, low-gradient slopes. Haplocambids areon steeper slopes, and Natrargids occur onfans where erosional processes have accumu-lated high-sodium materials.

WY40: Ustic Haplocambids and UsticTorriorthents, coarse-loamy, mixed; andTypic Torrifluvents, loamy-skeletal, mixed,frigid. This landscape has shallow and moder-ately deep Haplocambids and Torriorthentsoccurring on slopes along ephemeral chan-nels and Torrifluvents along gully bottoms.

WY41: Aridic Haplustolls and Ustic Haplo-cambids, fine-loamy, frigid. These soils are onTertiary age parent materials along the edgesof the basins under sagebrush-grasslands. TheHaplustolls are on sites with extra moisture,which promotes greater productivity.

Rationale for Soil Map Units

This map shows the

10 soil zones used in

the Digital Soils Map

of Wyoming.

Zone 1Zone 2 Zone 4

Zone 3

Zone 5Zone 6

Zone 7Zone 8

Zone 9

Zone 10

Zone 1: This zone features high mountainsthat were heavily glaciated. The most com-mon well-drained forest soils areDystrocryepts. Haplocryalfs occur on oldertill parent material (Bull Lake till of 140,000years plus age) and on low-relief surfaces.Soils along riparian areas are Cryaquepts,with inclusions of Histisols. The default map-ping unit (WY01) is the most extensive unit.Along the larger alluvial areas, the soils areaffected by a high water table (WY02), withsome inclusions of Cryofluvents. At high el-evations, in the rugged, glaciated peaks andridges, the soils are Cryorthents and HumicDystrocryepts, with extensive areas of rockoutcrop and talus (WY03).

Zone 2: This zone includes extensive areas ofglaciated extrusive volcanic mountains. Thedefault soil mapping unit is WY03. The veryhighest ridges and peaks, with very thin andpatchy soil cover, comprise WY04. Larger al-luvial valley floors, including old terraces, areoccupied with a complex of Cryaquepts andHumic Dystrocryepts (WY05).

Zone 3: This extensive unit is comprised ofhigh mountains that were heavily glaciated.The landscape is largely occupied by Dystro-cryepts and Haplocryalfs under continuousforest, with Haplocryolls under grass andshrubs in parks or openings in the forest.These parks are more common on dry (southand west) aspects than on north-facingslopes. Cryaquepts occur along the streams.This is soil mapping unit WY06. At lowerelevations (below 8,000 feet), the tempera-ture regime is frigid, and the landscape is oc-cupied by WY42. On Cretaceous shales, soiltextures are much finer and the mapping unitis WY07. At highest elevations, on glaciatedpeaks and ridges, the soils are thin and patchy,with large areas of rock outcrop (WY08).

Zone 4: In this intermountain basin environ-ment, the default mapping unit is a complexof Haplargids and Haplocalcids on low-gradi-ent surfaces, and Torriorthents on slopingsurfaces (WY09). Psamments occur on stabi-lized dunes (WY10) and gypsum-affectedand soluble salt-affected soils occur on playas(WY11). Where bedrock is exposed alongridges, the soils are Torriorthents with finetexture on Cretaceous shales (WY13) andloamy texture over other bedrocks (WY12).Footslopes occupied by local colluvium/allu-vium are occupied by Haplargids andNatrargids, depending upon the sodium con-tent of the parent material (WY14), and thealluvial valley floors in this arid setting areoccupied by Torrifluvents and Haplocambids,with the latter on the older Holocene sur-faces.

Zone 5: The default soil mapping unit forthis landscape is a complex of Haplocalcidsand Haplargids, with Mollisols (Haplustolls)on the more favorable sites. Above 5,000 feetelevation, the soil temperature regime isfrigid and the soils are a complex ofHapludolls and Hapludalfs, the latter underPonderosa Pine and Douglas Fir. Speciallandscape components include playas(WY19), mined land (WY18), and karst to-pography (WY17).

Zone 6: The Black Hills support an associa-tion of Mollisols (Argiudolls) under grass-lands and Alfisols (Hapludalfs) under forests.Many soils are fine textured (fine or fine-loamy families). Below 5,000 feet in eleva-tion, the soils are similar to those in the Pow-der River Basin (Haplocambids andHaplargids). Along streams, the soils areHaplaquolls and Fluvents.

11

Zone 7: The landscape in southeastern Wyo-ming is dominated by extensive outcrops ofTertiary-age parent materials. Above 6,500feet in elevation, the soils are Argiudolls andHapludolls, except for areas where the WhiteRiver formation is exposed; here the soils areshallow Entisols and Aridisols. Highest eleva-tions in the area support Inceptisols underforest and Mollisols under grass.

Zone 8: The Medicine Bow Mountains areoccupied by an association of Haplocryalfsand Dystrocryepts on forested sites. TheHaplocryalfs occur on low-relief surfaces ofBull Lake or older age. Dystrocryepts occurunder forest on Pinedale glacial deposits andon steep slopes of all ages. Grassy openings inthe forest and sage-grasslands in the foothillsare typically occupied by Typic Haplocryolls.Alpine areas are occupied by a complex ofHumic Dystrocryepts and Cryorthents. Ri-parian areas are usually occupied byCryaquepts, with a few Histisols present.

Zone 9: The Laramie and Wind River Basinsare rimmed with upturned Cretaceous andolder sedimentary rock. Soils developed onthese parent materials are typically an associa-tion of Natrargids and Torriorthents. The in-teriors of the basins are filled with alluvial

sediments of Tertiary and Pleistocene age.Soils on older alluvial surfaces (700,000 yearsand older) are usually dominated by calciumaccumulations (Petrocalcids andHaplocalcids) while younger, low-relief sur-faces are occupied by Haplargids (Pleistocenesurfaces) or Haplocambids (Holocene sur-faces). A complex of Natrargids andHaplargids occupies broad uplands developedin Tertiary-age parent materials. Riparian ar-eas often contain Haplaquolls, and steepscarps are typically occupied by Torriorthents.

Zone 10: The landscape in this extensive ba-sin environment is dominated by the broadexposure of Tertiary shales and sandstones,many of which are noted for their rich fossilrecord. Soils on the tertiary bedrock are anassociation of Haplocambids andTorriorthents, with Fluvents along ephemeralchannels and Mollisols on favorable sites.The zone contains Psamments on stabilizedsand dunes and salinized soils in playas. So-dium-affected soils (Natrargids) occur on al-luvial fans on high-sodium parent materials,and an association of Haplocryolls,Dystrocryepts, and Haplocryalfs occur above7,800 feet in elevation. Uplifted areas of cre-taceous and older rock add to the complexityof the area.

12

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13

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16

Appendix I

control section is intended to indicate equiva-lent amounts of soil moisture, and its upperand lower boundaries vary with soil waterholding capacity. It is roughly betweendepths of 10 and 30 cm (4 and 12 in) formost soils, and at greater depths for moder-ately coarse and coarse textured soils. Themoisture regimes are generally definitive cri-teria of the higher categories of soil taxonomyand are indicated by formative elements innames of many of the great groups. Thearidic moisture regime is one of the criteriathat defines the Aridisol Order.

The aridic, ustic, udic, aquic, and xeric mois-ture regimes are recognized in Wyoming. Ab-breviated definitions of the moisture regimesas they apply in Wyoming are given in thefollowing paragraphs. In these definitions,reference is to moisture levels within the con-trol section. “Dry” means too dry for mostplant growth, or above 15 bars moisture ten-sion; “moist” means soil water present at lessthan 15 bars tension; “prolonged summer dryperiod” means the control section is dry formore than 45 consecutive days after June 21;“saturated” means the profile is subject to ahigh water table for a significant part of theyear; “warm enough for plant growth” meansabove 5oC at a soil depth of 50 cm; “above8oC” refers to temperatures at this samedepth. The moisture regimes describe themoisture conditions that prevail in most years(6 out of 10 for xeric soils; 7 out of 10 forothers).

Soils with the aridic (or torric) soil moistureregime are dry more than half of the timewhen they are warm enough for plant growthand are never moist in any part for 90 con-

Soil Moisture and Soil TemperatureRegimes

Soil moisture and soil temperature regimesare defined in terms of field measurementsand are important characteristics of soils. Be-sides the direct effect of climate, they are alsoinfluenced by such factors as slope, aspect,plant cover, permeability, and water table.These regimes are used at different levels oftaxonomy to define the classes of soils. Forsome soils, these climatic-related criteria de-fine classes of orders, suborders, and greatgroups as indicated by formative elements ofmany soil names used in the legend. Soilmoisture and soil temperature regimes areused as one basis for separating different mapunits. Therefore, the legend is presented un-der subheadings that group the units accord-ing to ranges of soil moisture and tempera-ture. Brief definitions of the temperature andmoisture regimes in Wyoming are given be-low; the complete definitions are given inSoil Taxonomy (Soil Survey Staff 1975; SoilSurvey Staff 1998).

Soil Moisture Regimes

The amounts and seasonal incidence of waterthat enter the soil profile and percolatethrough, or are held and used by plants, areimportant properties of the soil affecting itsuse. Through geologic time, it has been acontrolling determinant of processes thathave formed the soil. The moisture regimesgenerally are related to climate and usuallyare estimated from climatic data. The defini-tions, however, are given in terms of long-term average seasonal soil moisture condi-tions within an upper portion of the profilecalled the soil moisture control section. The

17

secutive days when they are warmer than8oC. Aridic soils are described here as aridand semiarid. They generally have annualprecipitation of less than 36 cm (14 in.).These soils are too dry for annual croppingand many require irrigation for crop produc-tion. “Torri-” is a formative element indicat-ing aridic great groups of orders other thanAridisols (e.g., Entisols-Torriorthents).

Soils of the aquic soil moisture regime aresaturated by a seasonal or permanent highwater table and subject to reducing condi-tions reflected by mottled and grayish subsoilcolors (called redoximorphic features). Whenthe whole soil (from the surface down) issaturated for sufficient time, aquic subordersare used. Aquic subgroups are used for soilswhen saturated conditions prevail lower inthe profile. When the water table in the soilis contiguous with the ground water table,the soil is said to have “endosaturation.”When the water table in the soil is perchedabove a non-saturated layer (within 2 metersof the surface), the soil is said to have“episaturation.” When a soil has a water tableas the result of irrigation or other human ac-tivity, the soil is said to have “antric satura-tion.” Except for Aridisols, aquic suborderclasses are used in all orders in Wyoming.These classes are designated by the formativeelement “aqu-” in the name. Such soils arecommonly described as wet.

Soils of the udic soil moisture regime are usu-ally moist. They are not dry in any part for aslong as 90 cumulative days and do not have aprolonged summer dry period. They arenever wet except for short periods. These soilshave sufficient moisture for annual croppingor good forest and range production. Theyare commonly described as humid. Nearly allsoils with udic moisture regimes in Wyoming

are in mountains and most are cold. The for-mative element “ud-” does not appear ingroup names of these cold soils (e.g.,Haplocryalfs). Temperature is given prece-dence.

Soils with a ustic soil moisture regime are dryin some or all parts for 90 or more cumula-tive days but not dry in all parts more thanhalf of the time when they are warm, andthey do not have a prolonged summer dryperiod. These soils have limited soil moisture,but the moisture normally occurs mainlyduring the growing season. They are de-scribed as semiarid or sub-humid. In years ofaverage or above average rainfall with favor-able distribution, these soils can be annuallycropped. “Ust-” is the formative element usedin ustic great groups of Entisols andInceptisols.

Soil Temperature Regimes

Soil temperature regimes are defined in rela-tion to the mean summer soil temperaturesand the mean annual soil temperatures mea-sured at a depth of 50 cm (20 in) or at thecontact with bedrock, if shallower. Only thefrigid, cryic, and mesic temperature regimesoccur extensively in Wyoming. The formativeelement “bor-” is used in frigid or cryicMollisols suborders (except Aquolls) andAlfisol suborders (except Aqualfs); “cry-” isused in names for cryic great groups of all or-ders in Wyoming except Aridisols.

The frigid soil temperature regime has meanannual soil temperatures below 8oC (47oF)but above 0oC (32oF). The Borolls are subor-ders of Mollisols, and Boralfs are suborders ofAlfisols that are frigid or colder. In other sub-orders and orders, frigid temperatures are rec-ognized at the family level. Frigid soils are de-scribed as cool.

18

The cryic soil temperature regime also hasmean annual soil temperatures between 0oCand 8oC (32oF and 47oF), but, in addition,cool summer temperatures. Specifically, meansummer soil temperatures (June, July, andAugust) are below 15oC (59oF). They are be-low 8oC (47oF) if a surface organic layer (for-est floor) is present and below 13oC (55oF) ifthe soil is saturated and has no surface or-ganic layer. These somewhat complicatedlimits are designed to group equivalent soiltemperatures that differ because of the insu-lating effect of surface organic layers or theextra heat absorption by excess water. Cryicsoils are described as cold.

The mesic soil temperature regime has meanannual soil temperatures between 8oC (47oF)and 15oC (59oF). This temperature regime istypical of the middle latitudes, including themidwest corn belt. Major areas of soils withmesic temperature regimes occur in the Big-horn Basin and in eastern Wyoming from theBlack Hills (low elevations) to the Coloradostate line. Smaller areas occur around Casperand Rock Springs.

In addition to the three temperature regimesdiscussed above, which occur extensively in

Wyoming, the following temperature regimesare recognized:

Pergellic: Mean annual soil temperature(MAST) <0oC (32oF). Permafrost occurs inmoist soils with this temperature regime. Pat-terned ground is common as a result of frostaction. In Wyoming, small areas at high el-evations in the alpine have this temperatureregime.

Thermic: MAST is >15oC (59oF) but <22oC(72oF) and the difference between mean sum-mer and mean winter soil temperatures at 50cm is 5oC.

Hyperthermic: MAST is >22oC (72oF) andthe difference between mean summer andmean winter soil temperatures is >5oC.

The pergellic regime is typical of Arctic andAntarctic regions. The thermic regime is typi-cal of the cotton belt in the United States,and the hyperthermic zone is typical of thetropics. The prefix “iso-” is used with mesic,thermic, and hyperthermic regimes when thedifference between mean summer and meanwinter soil temperatures at 50 cm is <5oC(9oF).

19

Appendix II

ation or development of horizons. Entisolscan be in any climate and may be alkaline oracid in reaction. Those developing in recentalluvial deposits are stratified (Fluvents) orwet (Aquents). Most are on steep and verysteep slopes (Orthents), and some are onsandy, often wind-reworked materials(Psamments).

Histisols: Histisols are organic soils formedin bogs, wet meadows, and some backwaterfloodplain areas with a high water table. Theyinclude the peat and muck soils. These soilsare of minor extent in Wyoming and aremostly found at high elevations.

Inceptisols: Inceptisols include light coloredsoils (Ochrepts) that have had slight to mod-erate alteration during formation. They lackhorizons of clay accumulation but have sub-soil horizons differentiated by color, struc-ture, and some leaching of carbonates.Inceptisols occur under cool and cold tem-peratures and moderately low to high precipi-tation. They have formed either under grassor forest vegetation and are alkaline or acid inreaction. They are common in the forestedmountains of Wyoming.

Inceptisols in the Wyoming mountains haveformed under the influence of high precipita-tion, cold temperatures, and coniferous for-est. They are common on Late Wisconsin(Pinedale) and younger surfaces. SomeInceptisols along streams and in wet moun-tain meadows have high water tables andmottled grayish subsoils (Aquepts).

Mollisols: Mollisols are dark colored, base-rich soils formed under grass and, in someplaces, under open forest vegetation. They

Descriptions of the Soil Orders

Alfisols: Alfisols are light colored, slightly tomoderately acid soils with brownish subsoilhorizons of clay accumulation. They aresomewhat leached, but they are usually mod-erate to high in bases. Alfisols have formedunder coniferous or mixed forests with mod-erately low to high precipitation and cool orcold climates (frigid Udalfs and Cryralfs).They are primarily on mountains and foot-hills or in forested intermountain valleys. Inwestern Wyoming valleys, some Alfisols aredry for extended periods of the summer,though moist most of the year (Xeralfs).

Aridisols: Aridisols are light colored soils ofdry regions that are depleted of plant-avail-able soil moisture for most of the summer.They are unleached and are alkaline in reac-tion. Some Aridisols have developed horizonsof clay accumulation (Argids), mainly onolder and more stable surfaces. These mayalso be sodium affected. Others have onlysome redistribution of clay and weak-to-strong accumulations of calcium carbonate ormore soluble salts (Calcids, Gypsids,Cambids). Aridisols are common in the Wyo-ming plains and basins. They have shrub-grass or shortgrass prairie vegetation with afew juniper and stunted Ponderosa Pine inplaces. In Wyoming, many Aridisols are con-sidered to be intergrading to Mollisols withsomewhat more available moisture than typi-cal and are dry-farmed in some areas (e.g.,Ustic Haplargids).

Entisols: Entisols are very young soils. Someare developing in recently deposited parentmaterials, while others are on steep slopes, areactively eroding, and show little, if any, alter-

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may or may not have subsoil horizons of clayaccumulation. Typically, they have prismaticand blocky subsoil structure. Most have lowersubsoil horizons of calcium carbonate accu-mulation. Some are calcareous to the surface,and some are sodium affected. Mollisols oc-cur under moderate to low precipitation andcool to cold temperatures (frigid Udolls andCryolls) throughout Wyoming. Generally,the Mollisols of foothills and mountains withmoderate precipitation have a relatively thick,nearly black surface horizon and are deeplyleached of carbonates. Those formed on theplains and in basins under low precipitationare associated with Aridisols. They usuallyhave thinner and lighter colored surface hori-zons and are less deeply leached of carbon-ates. Mollisols of low-lying areas with highwater tables have mottled or grayish subsoils(Aquolls). In western Wyoming valleys, someMollisols are dry for extended periods of timein the summer, though moist most of theyear (Xerolls).

Spodosols: Spodosols are light colored, acid,brownish soils found occasionally under co-niferous forests in the Wyoming mountains.Precipitation is relatively high and tempera-tures are cold. They are characterized by hav-ing brownish or reddish brown, loamy orsandy, thin subsoil horizons with amorphoushumus, aluminum, and iron accumulation.Typically, these soils have a thin, light graysubsurface horizon beneath a dark organicduff layer of decomposing plant litter.Spodosols are common in the taiga of Eurasiaand North America but are rare in theRockies.

Vertisols: Vertisols are very clayey soils thathave deep, wide cracks when dry, and thatswell tightly when wet. Expanding clays of

this type are common in intermountain ba-sins in Wyoming in clayey soils derived fromshale. Vertisols have “slickensides” andwedge-shaped peds. Many soils that are verticintergrades in other orders also occur.

Andisols: Andisols are soils which have devel-oped on rather young (geologically) volcanicejectra (ash, cinders, pumice, etc.). They typi-cally have low bulk densities compared toother mineral soils (0.4 to 0.9 g cm-3). Thesesoils are often fertile, with high water-holdingcapacities and are highly productive for for-estry and crops. They may be thixotropic,however, and generally have poor engineeringproperties. They are common in the PacificNorthwest but rare in Wyoming (some arefound in the Yellowstone Park area).

Other Orders

Ultisols, Oxisols, and Gelisols: These are theremaining three soil orders. Soils in these or-ders are not recognized in Wyoming, al-though soils fitting these concepts developedin what is now Wyoming under previous cli-matic (tropical) conditions. Some of the redcolors seen in the Wyoming badlands arerelict Ultisols, dating from a time and climatewhen crocidiles and flamingos lived in whatis now Wyoming.

Ultisols are forest soils similar to Alfisols ex-cept they are more highly leached. Base satu-ration is low (<35%) and the argillic orkandic horizon is normally dominated by 1:1(Kaolinitic) type clays. Ultisols are commonin the southeastern United States, in the Pa-cific Northwest, and in the tropics. A fewUltisols occur in Wyoming, but the combina-tion of argillic horizons and < 35% base satu-ration is rare.

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Oxisols are soils of great age found on stableland surfaces in the tropics and subtropics.They are highly leached and contain mostlyiron and aluminum sesquioxides and 1:1 typesilicate clays in the clay particle size fraction.In the United States, oxisols occur only inHawaii and Puerto Rico. Relicts of oxisolshave been identified in California and Texas,representing past tropical climates.

Gelisols are soils with permafrost (i.e.,pergellic temperature regimes). Gelisols arecommon in the arctic and antarctic regions,and they also occur at high elevation in thenorthern and central Rocky Mountains.Plant root growth in Gelisols is restricted tothe active layer, the shallow surface layer thatthaws during the growing season. Gelisols aresensitive to disturbance since removal of thevegetation canopy or soil litter layer may re-sult in thawing of the permafrost layer.

APPENDIX III

Soil Data Layer � Decision Rules

The state was divided into 10 soil zonesbased on geologic province.

1. Yellowstone National Park area: moun-tains, cryic, udic.

2. Absaroka Volcanics: mountains, cryic,udic.

3. Middle Rocky Mountains: cryic, udic.

4. Bighorn Basin: intermountain basin,mesic, aridic.

5. Powder River Basin, Northern GreatPlains: mesic, aridic.

6. Black Hills: mountains, frigid, ustic.

7. Southeast Wyoming: Northern GreatPlains: frigid, aridic.

8. Medicine Bow and Laramie Mountains:mountains, cryic, udic.

9. Laramie and Wind River Basins: Wyo-ming basin, frigid, aridic.

10. Green River Basin: Wyoming basin,frigid, aridic.

The soils in each zone were assigned to par-ticular combinations of surficial geology andbedrock. Surficial geology units were groupedinto three major types, with four special cat-egories. A third classification element is eleva-tion. Throughout most of Wyoming, thebreak between frigid and cryic temperatureregimes occurs at approximately 7,800 feet.The break between mesic and frigid occurs at5,000 feet in northern Wyoming and at6,500 feet in southern Wyoming.

Landforms (from Surficial Geology Map ofWyoming 25 Element Classification; Case,Arneson, and Hallberg 1998):

Residual: aR, bi, bdi, mi, tre, ri, ui, Ri, Ki, ki,xi, Ti.

Alluvial: Ai, ai, ti, tdi, oai.

Colluvial: fi, fdi, li, sci.

Special: eolian (ei); glacial (gi); playas (pea);mined (Mi)

Bedrock geology (Love and Christiansen1985) was either keyed on the first letter ofthe code from the state bedrock geology map,or an individual unit is named specifically.

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Key to the Wyoming State Soils Map-ping Units (SMU)

Water: major lakes (Yellowstone Lake, TetonLake) and reservoirs.

Soil Zone 1:Default SMU is Dystrocryepts-Haplocryalfs,loamy-skeletal, mixed; and Cryaquepts, fine-loamy over sandy or sandy-skeletal, mixed(WY01).

If landform is Alluvial, then SMU isHaplocryolls, fine-loamy, mixed; andCryaquepts, fine-loamy over sandy or sandy-skeletal, mixed (WY02).

If landform is Ri, then SMU is Cryorthentsand Humic Dystrocryepts, loamy-skeletal,mixed; and Cryaquepts, fine-loamy oversandy or sandy-skeletal, mixed (WY03).

Soil Zone 2:Default SMU is WY03.

If landform is Residual, then SMU isCryorthents, loamy-skeletal, mixed; rock out-crop; and Cryaquepts, fine-loamy over sandyor sandy-skeletal, mixed (WY04).

If landform is ai or ti, then SMU isCryaquepts fine-loamy over sandy or sandy-skeletal, mixed; and Humic Dystrocryepts,loamy-skeletal, mixed (WY05).

Soil Zone 3:Default SMU is Haplocryalfs, Dystrocryepts,and Haplocryolls, loamy-skeletal, mixed; andCryaquepts, fine-loamy over sandy or sandy-skeletal, mixed (WY06).

If elevation is less than 7,800 ft, SMU isHapludolls and Haplboralfs, loamy-skeletal,mixed (WY42).

If bedrock is any K-- unit (Cretaceous) andelevation is greater than 7,800 ft, then SMU

is Haplocryolls, fine-loamy, mixed;Haplocryerts, fine, smectitic; andCryaquepts, fine-loamy, mixed (WY07).

If landform is Residual, Bedrock is other thanK, and elevation is greater than 7,800 ft,SMU is rock outcrop and Cryorthents,loamy-skeletal , mixed (WY08).

Soil Zone 4:Default SMU is Haplargids andHaplocalcids, fine-loamy over sandy orsandy-skeletal, mixed, mesic; andTorriorthents, fine-loamy and coarse-loamy,mixed, mesic (WY09).

If landform is ei, SMU is Torripsamments,mesic (WY10).

If landform is pea, SMU is Haplosalids, fine,smectitic, mesic (WY11).

If landform is Residual, SMU isTorriorthents, loamy, mixed, mesic; and rockoutcrop (WY12).

If landform is Residual and Bedrock is any K-- unit, SMU is Torriorthents, fine, mixed,mesic; and rock outcrop (WY13).

If landform is Colluvial, SMU is Haplargidsand Natrargids, fine-loamy or coarse-loamy,mixed, mesic (WY14).

If landform is ai, SMU is Torrifluvents,sandy-skeletal, mixed, mesic andHaplocambids, fine-loamy over sandy orsandy-skeletal, mixed, mesic (WY15).

Soil Zone 5:Default SMU is Haplargids, Haplocalcids,and Haplustolls, fine-loamy, mixed, mesic;and Torriorthents, loamy-skeletal, mixed,mesic (WY16).

If elevation is greater than 5,000 ft, SMU isWY42.

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If landform is ki, SMU is Torriorthents,loamy-skeletal, mixed, mesic; and rock out-crop (WY17).

If landform is Mi, SMU is Torriorthents andHaplustolls, fine-loamy, mixed, mesic(WY18).

If landform is pea, SMU is Haplogypsids,fine, smectitic, mesic (WY19).

Soil Zone 6:Default SMU is Haplargids andHaplocambids, fine and fine-loamy, mixed,mesic (WY43).

If elevation is greater than 5,000 ft, DefaultSMU is Hapludalfs and Argiudolls, fine-loamy, mixed, frigid; and Haplaquolls, fine,mixed, frigid (WY20).

If landform is Alluvial and elevation is greaterthan 5,000 ft, SMU is Argiudolls andHaplaquolls, fine-loamy, mixed, frigid(WY22).

If landform is Alluvial, SMU is WY15

If bedrock is any K-- unit, SMU isHaplocambids and Torriorthents; fine,mixed, mesic; and rock outcrop (WY21).

Soil Zone 7:Default SMU is Argiudolls, fine-loamy,mixed, frigid; and Argiudolls, fine-loamy oversandy or sandy-skeletal, mixed, frigid(WY23).

If landform is ei, SMU is WY10.

If bedrock is Twr, SMU is Haplocambids andTorriorthents, fine, mixed (WY24).

If elevation is less than 6,500 ft, SMU isWY44.

If bedrock is any P--- unit (Permian andPennsylvanian), SMU is Torriorthents and

Haplustepts, loamy-skeletal, mixed, frigid(WY25).

If bedrock is any K--- unit, SMU isTorriorthents and Haplocambids, fine,mixed, frigid (WY26).

If landform is ai, SMU is Torrifluvents andHaplaquolls, fine-loamy over sandy or sandy-skeletal, mixed, frigid (WY27).

Soil Zone 8:Default SMU is Haplocryalfs andDystrocryepts, loamy-skeletal, mixed; andHaplocryolls, fine-loamy, mixed (WY28).

If elevation is less than 7,800 ft, SMU isHapludalfs and Haplustepts, loamy-skeletal,frigid. (WY45).

If landform is Alluvial, SMU is Cryaqueptsand Cryaquolls, fine-loamy over sandy orsandy-skeletal, mixed (WY29).

If bedrock is Ys or Yla, SMU is Dystrocryeptsand Cryorthents, loamy skeletal, mixed; androck outcrop (WY30).

If bedrock is any K--, P-- or Tr-- (Triassic)unit, SMU is Dystrocryepts and Cryorthents,loamy-skeletal, mixed (WY31).

If bedrock is Wgn, SMU is Dystrocryepts,loamy-skeletal, mixed; and rock outcrop(WY32).

Soil Zone 9:Default SMU is WY09. (Note: In this region,this unit is frigid.)

If landform is ei, SMU is WY10.

If elevation is greater than 7,800 ft, SMU isWY31.

If elevation is less than 5,500 ft, SMU isHaplargids and Torrifluvents, fine-loamy over

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sandy or sandy-skeletal, mixed, mesic(WY44).

If bedrock is Wgn, SMU is Torriorthents,loamy-skeletal, mixed, frigid; and rock out-crop (WY33).

If bedrock is any T-- (Tertiary) unit, SMU isHaplargids and Natragids, fine-loamy, mixed,frigid (WY34).

If bedrock is Tr-- or K--, SMU is Natrargidsand Torriorthents, fine, mixed, frigid(WY35).

If bedrock is P--, SMU is Torriorthents andHaplocalcids, coarse-loamy, mixed, frigid(WY36).

If bedrock is Qt, SMU is Petrocalcids andCalciargids, fine-loamy over sandy or sandy-skeletal, mixed, frigid (WY37).

If bedrock is Qa, SMU is Haplocambids andHaplargids, coarse-loamy, mixed, frigid(WY38).

Soil Zone 10:Default SMU is Haplargids, Haplocambids,and Natrargids, fine-loamy, mixed, frigid(WY39).

If landform is ei, SMU is WY10.

If elevation is greater than 7,800 ft, SMU isWY06.

If elevation is less than 6,500ft,. SMU isWY44.

If bedrock is Tw, Tgw or Tgrw, SMU isHapludolls and Haplocambids, fine-loamy,mixed, frigid (WY41).

If landform is Residual, SMU is WY17.

If landform is Colluvial and Bedrock is T--,SMU is Haplocambids and Torriorthents,coarse-loamy, mixed, frigid; andTorrifluvents, loamy-skeletal, mixed, frigid(WY40).

If landform is pea, SMU is WY11.

If landform is Alluvial, SMU is WY27.

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