Natural Resources
Conservation Service
Ecological site R034AY260WY
Shallow Igneous
Foothills and Basins West (SwIg)
Accessed: 06/27/2026
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Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
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Figure 1. Mapped extent
Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated.
Associated sites
R034AY258WY Shallow Clayey Foothills and Basins West (SwCy)
Shallow Clayey
R034AY262WY Shallow Loamy Foothills and Basins West (SwLy)
Shallow Loamy
Similar sites
R034AY216WY Igneous Foothills and Basins West (Ig)
Igneous 10-14W has lower production and does not have bitterbrush as a major woody component.
R034AY263WY Shallow Loamy Calcareous Foothills and Basins West (SwLyCa)
Shallow Loamy, calcareous 10-14W does not have bitterbrush as a major woody component.
R043BY260WY Shallow Igneous Foothills and Mountains West
Shallow Igneous 15-19W has higher production.
Table 1. Dominant plant species
Tree Not specified
Shrub Not specified
Herbaceous Not specified
Physiographic features
This site is found in an upland position on rolling to steep slopes and ridges. Slopes are commonly 15 to 30%.
Table 2. Representative physiographic features
Landforms (1) Escarpment
(2) Ridge
Flooding frequency None Ponding frequency None Elevation 6500 – 7500 ft Slope 5 – 70 % Ponding depth 0 in Aspect Aspect is not a significant factor Climatic features
Annual precipitation ranges from 10-14 inches per year. Wide fluctuations may occur in yearly precipitation and result in more dry years than those with more than normal precipitation. Temperatures show a wide range between summer and winter and between daily maximums and minimums. This is predominantly due to the high elevation and dry air, which permits rapid incoming and outgoing radiation. Cold air outbreaks in winter move rapidly from northwest to southeast and account for extreme minimum temperatures. Extreme storms may occur during the winter, but most severely affect ranch operations during late winter and spring.
Daytime winds are generally stronger than nighttime and occasional strong storms may bring brief periods of high winds with gusts to more than 50 mph.
Growth of native cool season plants begins about April 15 and continues to about August 15. Some green up of cool season plants usually occurs in September depending upon fall moisture occurrences.
For detailed information visit the Natural Resources Conservation Service National Water and Climate Center at http://www.wcc.nrcs.usda.gov/cgibin/state.pl?state=wy website. Other climate stations representative of this precipitation zone include ”Border 3 N ” and Kemmerer Wtr Trtmt” in Lincoln County; “Evanston 1 E” in Uinta County; and “Merna” in Sublette County.Table 3 Representative climatic features
Frost-free period (average) 70 days Freeze-free period (average) 100 days Precipitation total (average) 10 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
There are no water features associated with this site.
Soil features
These shallow, well drained soils are on bedrock-controlled mountain sides and foothills. Coarse fragment percentage is commonly more than 35 percent, but may be less in the surface layer. Parent material is residuum and colluvium from granite and schist with the soil texture modifiers of gravelly cobbly, and very cobbly.
Subsurface Texture Group: very cobbly sandy loam
Table 4. Representative soil features
Surface texture (1) Gravelly loam
(2) Gravelly sandy loam
(3) Cobbly sandy loam
Family particle size (1) Loamy
Drainage class Well drained to somewhat excessively drained Permeability class Moderate to moderately rapid Soil depth 10 – 20 in Surface fragment cover <=3" 10 – 25 % Surface fragment cover >3" 20 – 45 % Available water capacity
(0-40in)0.6 – 1.2 in Calcium carbonate equivalent
(0-40in)Not specified Soil reaction (1:1 water)
(0-40in)5.6 – 7.2 Subsurface fragment volume <=3"
(Depth not specified)15 – 30 % Subsurface fragment volume >3"
(Depth not specified)30 – 50 % Ecological dynamics
As this site deteriorates, species such as big sagebrush and green rabbitbrush will increase. Bluebunch wheatgrass, needleandthread, Indian ricegrass, and bitterbrush will decrease in frequency and production.
These plant communities narratives may not represent every possibility, but they probably are the most prevalent and repeatable plant communities. The plant composition tables shown above have been developed from the best available knowledge at the time of this revision. As more data is collected, some of these plant communities may be revised or removed, and new ones may be added. None of these plant communities should necessarily be thought of as “Desired Plant Communities”. According to the USDA NRCS National Range and Pasture Handbook, Desired Plant Communities (DPC’s) will be determined by the decision-makers and will meet minimum quality criteria established by the NRCS. The main purpose for including any description of a plant community here is to capture the current knowledge and experience at the time of this revision.
The Historic Climax Plant Community (description follows the plant community diagram) has been determined by study of rangeland relic areas, or areas protected from excessive disturbance. Trends in plant communities going from heavily grazed areas to lightly grazed areas, seasonal use pastures, and historical accounts have also been used.
The following is a State and Transition Model Diagram that illustrates the common plant communities (states) that can occur on the site and the transitions between these communities. The ecological processes will be discussed in more detail in the plant community narratives following the diagram.
State and transition model
Custom diagramStandard diagram
More interactive model formats are also available. View Interactive Models
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textEcosystem states
State 1 submodel, plant communities
State 2 submodel, plant communities
State 3 submodel, plant communities
State 4 submodel, plant communities
State 1
Bitterbrush/Rhizomatous Wheatgrass (HCPC)Community 1.1
Bitterbrush/Rhizomatous Wheatgrass (HCPC)The interpretive plant community for this site is the Historic Climax Plant Community. Potential vegetation is about 65% grasses or grass-like plants, 10% forbs, and 25% woody plants.
The major grasses include rhizomatous wheatgrass, bluebunch wheatgrass, Indian ricegrass, needleandthread, and letterman needlegrass. Other grasses include Canby, mutton, and Sandberg bluegrass, needleleaf sedge, plains reedgrass, and prairie junegrass. Bitterbrush and black sagebrush are the dominant woody plants. Other woody plants include green rabbitbrush, snowberry, big sagebrush, skunkbush sumac, and winterfat.
A typical plant composition for this state consists of rhizomatous wheatgrass 20-35%, bluebunch wheatgrass 5-10%, needleandthread 5-10%, Indian ricegrass 5-10%, Letterman needlegrass 1-10%, other grasses and grass-like plants 10-20%, perennial forbs 5-10%, bitterbrush 5-15%, black sagebrush 5-10%, and 5-10% other woody species. Ground cover, by ocular estimate, varies greatly depending on the amount of exposed parent material, and herbage cover ranges from 25-30%.
The total annual production (air-dry weight) of this state is about 800 pounds per acre, but it can range from about 600 lbs./acre in unfavorable years to about 1100 lbs./acre in above average years.
The state is stable and well adapted to the Cool Central Desertic Basins and Plateaus climatic conditions. The diversity in plant species allows for high drought resistance. This is a sustainable plant community (site/soil stability, watershed function, and biologic integrity
Transitions or pathways leading to other plant communities are as follows:
• Nonuse will convert this plant community to the Bitterbrush/Black Sagebrush State.
• Heavy Continuous Season-Long Grazing will convert this plant community to the Big Sagebrush/Rhizomatous Wheatgrass State.
• Wildfire or Severe Ground Disturbance will convert this plant community to the Cheatgrass State.
Figure 4. Annual production by plant type (representative values) or group (midpoint values)
Table 5. Annual production by plant type
Plant type Low
(lb/acre)Representative value
(lb/acre)High
(lb/acre)Grass/Grasslike 390 520 715 Shrub/Vine 150 200 275 Forb 60 80 110 Total 600 800 1100 Figure 5. Plant community growth curve (percent production by month). WY0301 , 34AC, Upland Sites. All Upland Sites.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 5 40 50 5 State 2
Bitterbrush/Black SagebrushCommunity 2.1
Bitterbrush/Black SagebrushThis plant community is a result of nonuse. Bitterbrush and big sagebrush are significant components of this plant community, often making up 20-75% of the annual production. Dominant grasses include bluebunch wheatgrass, Indian ricegrass, and needleandthread.
The total annual production (air-dry weight) of this state is about 600 pounds per acre, but it can range from about 400 lbs./acre in unfavorable years to about 900 lbs./acre in above average years.
The state is stable and protected from excessive erosion. The biotic integrity of this plant community is usually intact, however forage value will decrease and wildlife values will shift toward different species. The watershed is functioning.
Transitional pathways leading to other plant communities are as follows:
• Prescribed Grazing will return this state to near Historic Climax Plant Community (Bitterbrush/Rhizomatous Wheatgrass State).
Figure 6. Plant community growth curve (percent production by month). WY0301 , 34AC, Upland Sites. All Upland Sites.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 5 40 50 5 State 3
Big Sagebrush/Rhizomatous WheatgrassCommunity 3.1
Big Sagebrush/Rhizomatous WheatgrassThis plant community is found under heavy, continuous season-long grazing. Big and black sagebrush, green rabbitbrush, and various forbs are significant components of this plant community. Dominant grasses in the understory include rhizomatous wheatgrass, Canby and Sandberg bluegrass, and Letterman needlegrass. Phlox and goldenweed are common forbs found on this site.
The total annual production (air-dry weight) of this state is about 400 pounds per acre, but it can range from about 200 lbs./acre in unfavorable years to about 600 lbs./acre in above average years.
Soil erosion is accelerated because of increased bare ground. The biotic community has been compromised, but is relatively stable. The watershed is functioning, but is at risk of further degradation. Water flow patterns and pedestals are obvious. Infiltration is reduced and runoff is increased.
Transitional pathways leading to other plant communities are as follows:
• Chemical Brush Management followed by deferment for 1 to 2 years as part of a Prescribed Grazing plan will return this state to near Historic Climax Plant Community (Bitterbrush/Rhizomatous Wheatgrass State). Care should be taken when planning brush management to consider wildlife habitat and critical winter ranges.
Figure 7. Plant community growth curve (percent production by month). WY0301 , 34AC, Upland Sites. All Upland Sites.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 5 40 50 5 State 4
CheatgrassCommunity 4.1
CheatgrassThis vegetation state currently is a result of wildfire or severe ground disturbance. Rabbitbrush flourishes and rhizomatous wheatgrass is the dominant understory grass. Other grasses include bluebunch wheatgrass and letterman needlegrass. Cheatgrass invades, effectively increasing the fire frequency and limiting the ability for non-sprouting woody plants to reestablish.
The total annual production (air-dry weight) of this state is about 100 pounds per acre, but it can range from about 50 lbs./acre in unfavorable years to about 250 lbs./acre in above average years.
The state is vulnerable to excessive erosion. The biotic integrity of this plant community is at risk depending on how far a shift has occurred in plant composition toward cheatgrass and annual forbs. The watershed is at risk as bare ground increases.
Transitional pathways leading to other plant communities are as follows:
• Chemical Seedbed Preparation and Re-seeding followed by deferment for 1 to 2 years as part of a Prescribed Grazing plan will return this plant community to near Historic Climax Plant Community (Bitterbrush/Rhizomatous Wheatgrass State) although cheatgrass will remain a part of the plant community. Additional deferment may be necessary and should be prescribed on an individual site basis.
Figure 8. Plant community growth curve (percent production by month). WY0301 , 34AC, Upland Sites. All Upland Sites.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 5 40 50 5 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 160–280 western wheatgrass PASM Pascopyrum smithii 160–280 – 2 40–80 bluebunch wheatgrass PSSP6 Pseudoroegneria spicata 40–80 – 3 40–80 needle and thread HECO26 Hesperostipa comata 40–80 – 4 40–80 Indian ricegrass ACHY Achnatherum hymenoides 40–80 – 5 8–80 Letterman's needlegrass ACLE9 Achnatherum lettermanii 8–80 – 6 80–160 Grass, perennial 2GP Grass, perennial 0–40 – needleleaf sedge CADU6 Carex duriuscula 0–40 – plains reedgrass CAMO Calamagrostis montanensis 0–40 – squirreltail ELEL5 Elymus elymoides 0–40 – prairie Junegrass KOMA Koeleria macrantha 0–40 – muttongrass POFE Poa fendleriana 0–40 – Sandberg bluegrass POSE Poa secunda 0–40 – Forb7 40–80 Forb, perennial 2FP Forb, perennial 0–40 – common yarrow ACMI2 Achillea millefolium 0–40 – rosy pussytoes ANRO2 Antennaria rosea 0–40 – milkvetch ASTRA Astragalus 0–40 – Indian paintbrush CASTI2 Castilleja 0–40 – pale bastard toadflax COUMP Comandra umbellata ssp. pallida 0–40 – tapertip hawksbeard CRAC2 Crepis acuminata 0–40 – fleabane ERIGE2 Erigeron 0–40 – buckwheat ERIOG Eriogonum 0–40 – aster EUCEP2 Eucephalus 0–40 – granite prickly phlox LIPU11 Linanthus pungens 0–40 – stoneseed LITHO3 Lithospermum 0–40 – bluebells MERTE Mertensia 0–40 – nailwort PARON Paronychia 0–40 – spiny phlox PHHO Phlox hoodii 0–40 – stonecrop SEDUM Sedum 0–40 – stemless mock goldenweed STAC Stenotus acaulis 0–40 – clover TRIFO Trifolium 0–40 – Shrub/Vine8 40–120 antelope bitterbrush PUTR2 Purshia tridentata 40–120 – 9 40–80 black sagebrush ARNO4 Artemisia nova 40–80 – 10 40–80 big sagebrush ARTR2 Artemisia tridentata 0–40 – yellow rabbitbrush CHVI8 Chrysothamnus viscidiflorus 0–40 – winterfat KRLA2 Krascheninnikovia lanata 0–40 – skunkbush sumac RHTR Rhus trilobata 0–40 – western snowberry SYOC Symphoricarpos occidentalis 0–40 – Table 7. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 8. Community 3.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 9. Community 4.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
Animal Community – Wildlife Interpretations
Bitterbrush/Rhizomatous Wheatgrass Plant Community (HCPC): Suitable thermal and escape cover for most wildlife is limited due to the low height and density of woody plants. Bitterbrush and sagebrush provide important winter forage for mule deer and elk. Year-round habitat is provided for sage grouse and many other sagebrush obligate species such as the sage sparrow, Brewer’s sparrow, sage thrasher, pygmy rabbit, sagebrush vole, horned lizard, and pronghorn antelope.
Bitterbrush/Black Sagebrush Plant Community: This plant community may be beneficial for the same wildlife that would use the Historic Climax Plant Community. However, the plant community composition is less diverse, and thus, less apt to meet the seasonal needs of these animals.
Big Sagebrush/Rhizomatous Wheatgrass Plant Community: This plant community may be beneficial for the same wildlife that would use the Historic Climax Plant Community. However, the plant community composition is less diverse, and thus, less apt to meet the seasonal needs of these animals.
Cheatgrass Plant Community: This plant community exhibits a low level of plant species diversity. In most cases it is not a desirable plant community to select as a wildlife habitat management objective.
Animal Community – Grazing Interpretations
The following table lists suggested stocking rates for cattle under continuous season-long grazing under normal growing conditions. These are conservative estimates that should be used only as guidelines in the initial stages of the conservation planning process. Often, the current plant composition does not entirely match any particular plant community (as described in this ecological site description). Because of this, a field visit is recommended, in all cases, to document plant composition and production. More precise carrying capacity estimates should eventually be calculated using this information along with animal preference data, particularly when grazers other than cattle are involved. Under more intensive grazing management, improved harvest efficiencies can result in an increased carrying capacity.
Plant Community Production (lb./ac) and Carrying Capacity* (AUM/ac)
Bitterbrush/Rhizomatous Wheatgrass (HCPC) 600-1100 lb./ac and .17 AUM/ac
Bitterbrush/Black Sagebrush 400-900 lb./ac and .14 AUM/ac
Big Sagebrush/Rhizomatous Wheatgrass 200-600 lb./ac and .07 AUM/ac
Cheatgrass 50-250 lb./ac and .02 AUM/ac
* - Continuous, season-long grazing by cattle under average growing conditions.
Grazing by domestic livestock is one of the major income-producing industries in the area. Rangeland in this area may provide yearlong forage for cattle, sheep, or horses. During the dormant period, the forage for livestock use needs to be supplemented with protein because the quality does not meet minimum livestock requirements.
Hydrological functions
Water is the principal factor limiting forage production on this site. This site is highly variable and is dominated by soils in hydrologic group B and C, with localized areas in hydrologic group D. Infiltration ranges from slow to very rapid. Runoff potential for this site varies from moderate to high depending on soil hydrologic group, depth and degree of bedrock fracturing, slope, and ground cover (refer to Part 630, NRCS National Engineering Handbook for detailed hydrology information).
Rills and gullies may be present, but should be small. Water flow patterns should be barely distinguishable. Pedestals are only slightly present in association with bunchgrasses such as bluebunch wheatgrass. Litter typically falls in place, and signs of movement are not common. Chemical and physical crusts are rare to non-existent. Cryptogrammic crusts are present, but only cover 1-2% of the soil surface.
Recreational uses
This site provides hunting opportunities for upland game species.
Wood products
No appreciable wood products are present on the site.
Other products
None noted.
Supporting information
Inventory data references
Information presented here has been derived from NRCS clipping data and other inventory data. Field observations from range trained personnel were also used. Those involved in developing this site include: Bill Christensen, Range Management Specialist, NRCS; Karen Clause, Range Management Specialist, NRCS; and Everet Bainter, Range Management Specialist, NRCS. Other sources used as references include: USDA NRCS Water and Climate Center, USDA NRCS National Range and Pasture Handbook, and USDA NRCS Soil Surveys from various counties.
Contributors
Karen Clause
Rangeland health reference sheet
Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.
Author(s)/participant(s) K. Clause, E. Bainter Contact for lead author karen.clause@wy.usda.gov or 307-367-2257 Date 03/16/2007 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
Some expected on this site. Where present, short and widely spaced. -
Presence of water flow patterns:
Some can be observed. -
Number and height of erosional pedestals or terracettes:
Rare to slight. -
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
Bare ground can range from 20-50%. -
Number of gullies and erosion associated with gullies:
Active gullies should not be present. -
Extent of wind scoured, blowouts and/or depositional areas:
Rare to nonexistent. -
Amount of litter movement (describe size and distance expected to travel):
Herbaceous litter expected to move in small amounts down-slope. Large woody debris from shrubs will show no movement. -
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
Soil Stability Index ratings range from 1 (interspaces) to 6 (under plant canopy), but average values should be 2.5 or greater. -
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
Soil data is limited for this site. Described A-horizons are about 4 inches (10 cm) with OM of .5 to 1%. -
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
Plant community consists of 25-85% grasses, 10% forbs, and 10-65% shrubs. Unevenly distributed plant canopy (30-60%) and litter, but moderate to rapid infiltration rates result in slight to minimal runoff. Basal cover is typically less than 5% for this site and does very little to effect runoff on this site. -
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
None. -
Functional/Structural Groups (list in order of descending dominance by above-ground annual-production or live foliar cover using symbols: >>, >, = to indicate much greater than, greater than, and equal to):
Dominant:
Sub-dominant:
Other:
Additional:
Mid-size, cool season bunchgrasses> perennial shrubs=cool season rhizomatous grasses>>perennial forbs>short, cool season bunchgrasses -
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
Minimal decadence, typically associated with shrub component. -
Average percent litter cover (%) and depth ( in):
Litter ranges from 5-20% of total canopy measurement with total litter (including beneath the plant canopy) from 20-60% expected. Herbaceous litter depth typically ranges from 3-10mm. Woody litter can be up to a couple inches (4-6 cm). -
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
English: 700-1200 lb/ac (900 lb/ac average); Metric 784-1344 kg/ha (1008 kg/ha average). -
Potential invasive (including noxious) species (native and non-native). List species which BOTH characterize degraded states and have the potential to become a dominant or co-dominant species on the ecological site if their future establishment and growth is not actively controlled by management interventions. Species that become dominant for only one to several years (e.g., short-term response to drought or wildfire) are not invasive plants. Note that unlike other indicators, we are describing what is NOT expected in the reference state for the ecological site:
Bare ground greater than 75% and the presence of Cheatgrass are the most common indicators of a threshold being crossed. Rabbitbrush, Wyoming big sagebrush, Sandberg bluegrass, and goldenweed are common increasers. Annual weeds such as Cheatgrass and mustards are common invasive species in disturbed sites. -
Perennial plant reproductive capability:
All species are capable of reproducing, except in drought years.
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