Natural Resources
Conservation Service
Ecological site R035XB279AZ
Clay Loam Upland
6-10" p.z.
Sodic, Gypsic
Last updated: 5/20/2025
Accessed: 05/05/2026
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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.
MLRA notes
Major Land Resource Area (MLRA): 035X–Colorado Plateau
AZ CRA 35.2 - Colorado Plateau Shrub – Grasslands
Elevations range from 3500-5500 feet and precipitation averages 6 to 10 inches per year. Vegetation includes shadscale, fourwing saltbush, Mormon tea, blackbrush, Indian ricegrass, galleta, blue grama, and black grama. The soil temperature regime is mesic and the soil moisture regime is typic aridic. This unit occurs within the Colorado Plateau Physiographic Province and is characterized by a sequence of flat to gently dipping sedimentary rocks eroded into plateaus, valleys and deep canyons. Sedimentary rock classes dominate the plateau with volcanic fields occurring for the most part near its margin.Ecological site concept
This site occurs on toeslopes of plateaus, footslopes of hills, and scarp faces and backslopes of benches and cuestas. This site also occurs on fan remnants.
The soils on this site are moderately deep (20-40") to very deep (60+") and well drained.
Surface textures include very fine sandy loam, channery loam and loam. These soils contain subsurface horizons with significant accumulations of gypsum. EC ranges from 8 to 16 mmhos/cm and SAR ranges from 13 to 30.Table 1. Dominant plant species
Tree Not specified
Shrub (1) Atriplex cuneata
(2) Atriplex corrugataHerbaceous (1) Achnatherum hymenoides
(2) Pleuraphis jamesiiPhysiographic features
This site occurs on toeslopes of plateaus, footslopes of hills, and scarp faces and backslopes of benches and cuestas. This site also occurs on fan remnants. It does not benefit from run-in moisture nor does it suffer from excessive loss from runoff. It occurs on all exposures.
Table 2. Representative physiographic features
Landforms (1) Fan remnant
(2) Plateau
(3) Cuesta
Flooding frequency None to very rare Ponding frequency None to rare Elevation 4800 – 5600 ft Slope 0 – 25 % Aspect Aspect is not a significant factor Climatic features
The climate of the land resource unit is arid with warm summers and cool winters. This is one of the driest land resource units on the Colorado Plateau with an average annual precipitation ranging from 6 to 10 inches per year. It is also very erratic, often varying substantially from year to year. 40 to 50 percent of the precipitation is received from October through early May. This precipitation comes as gentle rain or snow from frontal storms coming out of the Pacific Ocean. Snow is common from November through February. Generally no more than an inch or two of snow accumulates and usually melts within a day or two. The remaining precipitation, approximately 50 to 60 percent, is received from July through September as spotty, unreliable and sometimes violent thunderstorms. The moisture for this precipitation originates in the Gulf of Mexico (and the Pacific Ocean in the fall) and flows into the area on the north end of the Mexican monsoon. Late May through late June is generally a dry period. The mean annual temperature ranges from 53 to 56 degrees Fahrenheit (F). The frost-free period (air temperature > 32 degrees F) ranges from 135 to 160 days (@ 50 percent probability). Strong winds are common, especially in the spring.
Table 3 Representative climatic features
Frost-free period (average) 160 days Freeze-free period (average) 180 days Precipitation total (average) 10 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
This is an upland site, and is not associated with water features or wetlands. During heavy rain events, this site may receive run-on moisture from landforms above and contribute runoff to landforms below.
Soil features
The soils on this site are moderately deep (20-40") to very deep (60+") and well drained.
Surface textures include very fine sandy loam, channery loam and loam.
Subsurface textures include silty clay loam, loam, clay, clay loam, channery clay loam, silty clay, silty clay loam.
These soils are formed in alluvium and residuum derived from siltstone and shale. Hazard of erosion from water is moderate. Hazard from wind is moderate to severe. There is secondary gypsum at 10-30".
Typical taxonomic units include:
SSA 717 Shiprock NM - MU's 113 and 183 Gyptur, 137 Patel part, 167 Hoskay and Patel partsTable 4. Representative soil features
Parent material (1) Alluvium – shale and siltstone
Surface texture (1) Very fine sandy loam
(2) Channery loam
(3) Loam
Family particle size (1) Loamy
Drainage class Moderately well drained to well drained Permeability class Slow to moderately slow Soil depth 20 – 60 in Surface fragment cover <=3" 15 – 45 % Surface fragment cover >3" 0 – 10 % Available water capacity
(0-40in)0 – 7 in Calcium carbonate equivalent
(0-40in)5 – 15 % Electrical conductivity
(0-40in)8 – 16 mmhos/cm Sodium adsorption ratio
(0-40in)13 – 30 Soil reaction (1:1 water)
(0-40in)7.4 – 8.4 Ecological dynamics
The plant communities found on an ecological site are naturally variable. Composition and production will vary with yearly conditions, location, aspect, and the natural variability of the soils. The historical climax plant community represents the natural potential plant communities found on relict or relatively undisturbed sites. Other plant communities described here represent plant communities that are known to occur when the site is disturbed by factors such as grazing, fire, or drought.
Production data provided in this site description is standardized to air-dry weight at the end of the summer growing season. The plant communities described in this site description are based on near normal rainfall years.
NRCS uses a Similarity Index to compare existing plant communities to the plant communities described here. Similarity Index is determined by comparing the production and composition of a plant community to the production and composition of a plant community described in this site description. To determine Similarity Index, compare the production (air-dry weight) of each species to that shown in the plant community description. For each species, count no more than the maximum amount shown for the species, and for each group, count no more than the maximum shown for the group. Divide the resulting total by the total normal year production shown in the plant community description. If rainfall has been significantly above or below normal, use the total production shown for above or below normal years. If field data is not collected at the end of the summer growing season, then the field data must be corrected to the end of the year production before comparing it to the site description. The growth curve can be used as a guide for estimating production at the end of the summer growing season.State and transition model
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 1
Reference StateThis state represents the most ecologically stable conditions in terms of resistance to erosion. Moreover, this state has the highest potential for productivity and plant diversity.
Community 1.1
Historic Climax Plant CommunityThis site has a plant community made up primarily of mid grasses, short shrubs and a small percentage of forbs. In the original plant community, there is amixture of both cool and warm season grasses.
Plant species most likely to invade or increase on this site when it deteriorates are cheatgrass, annual barley, Russian thistle and Castle Valley clover. Continuous grazing during the winter and spring periods will decrease the cool season grasses, which are replaced by warm season, lower forage value grasses and shrubs.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)Shrub/Vine 180 200 220 Grass/Grasslike 160 180 200 Forb 4 12 20 Total 344 392 440 Figure 5. Plant community growth curve (percent production by month). AZ3521 , 35.2 6-10" p.z. all sites. Growth begins in the spring and continues through the summer. Most growth in this CRA occurs in the spring using stored winter moisture..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 0 1 9 20 27 14 10 11 5 3 0 0 Figure 6. Plant community growth curve (percent production by month). AZ5201 , 35.2 6-10" p.z. galleta. Growth begins in spring, most growth occurs during summer rains..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 0 0 5 10 20 10 15 35 5 0 0 0 Figure 7. Plant community growth curve (percent production by month). AZ5202 , Indian ricegrass, 35.2 6-10" p.z.. Growth begins in spring, most growth occurs in May, goes dormant during summer heat..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 0 0 10 15 40 20 0 0 10 5 0 0 Figure 8. Plant community growth curve (percent production by month). AZ5203 , 35.2 6-10" p.z. alkali sacaton. Growth begins in the spring, most growth occurs in the summer, goes dormant in the fall..
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec J F M A M J J A S O N D 0 0 5 10 20 10 20 20 10 5 0 0 State 2
Degraded StatePlant species most likely to invade or increase on this site when it deteriorates are cheatgrass, annual barley, Russian thistle and Castle Valley clover. Continuous grazing during the winter and spring periods will decrease the cool season grasses, which are replaced by warm season, lower forage value grasses and shrubs.
Dominant plant species
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cheatgrass (Bromus tectorum), grass
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prickly Russian thistle (Salsola tragus), other herbaceous
Transition T1A
State 1 to 2Prolonged continuous grazing. Plant species most likely to invade or increase on this site when it deteriorates are cheatgrass, annual barley, Russian thistle and Castle Valley clover. Continuous grazing during the winter and spring periods will decrease the cool season grasses, which are replaced by warm season, lower forage value grasses and shrubs.
Key drivers
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Wildlife grazing or browsing
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Livestock grazing or browsing
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Nonnative plant species presence and/or establishment
Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Shrub/Vine0 180–220 valley saltbush ATCU Atriplex cuneata 80–100 – mat saltbush ATCO4 Atriplex corrugata 20–40 – wheelscale saltbush ATELF Atriplex elegans var. fasciculata 0–20 – bud sagebrush PIDE4 Picrothamnus desertorum 0–20 – Shrub (>.5m) 2SHRUB Shrub (>.5m) 4–20 – shadscale saltbush ATCO Atriplex confertifolia 0–20 – Grass/Grasslike0 160–200 Indian ricegrass ACHY Achnatherum hymenoides 80–100 – James' galleta PLJA Pleuraphis jamesii 20–40 – alkali sacaton SPAI Sporobolus airoides 20–40 – squirreltail ELELE Elymus elymoides ssp. elymoides 4–20 – Grass, perennial 2GP Grass, perennial 0–8 – sand dropseed SPCR Sporobolus cryptandrus 0–4 – Forb0 4–20 Forb, perennial 2FP Forb, perennial 4–12 – globemallow SPHAE Sphaeralcea 0–8 – Forb, annual 2FA Forb, annual 0–8 – Interpretations
Animal community
This site is suitable for year-long grazing by all classes of livestock. Grazing systems adapt well to this site and should be used. When vegetation deteriorates this site is susceptible to erosion.
Wildlife species are transient on this site from adjacent areas.Recreational uses
The topography of this site and its grass-shrub texture gives good aesthetic appeal.
The winters are cold and spring time is usually windy. The summers are mild with typical southwest thunderstorms.
The main activities are photography, wildlife observation and hiking.
Supporting information
Type locality
Location 1: San Juan County, NM Township/Range/Section T29N R17W S16 General legal description Sulfur Springs quad - about 5 miles southeast of Shiprock, NM - Navajo Reservation NM. Contributors
Harmon Hodgkinson
Karlynn Huling
Larry D. EllicottApproval
Kendra Moseley, 5/20/2025
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) Contact for lead author Date 05/05/2026 Approved by Approval date Composition (Indicators 10 and 12) based on Annual Production Indicators
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Number and extent of rills:
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Presence of water flow patterns:
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Number and height of erosional pedestals or terracettes:
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Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
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Number of gullies and erosion associated with gullies:
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Extent of wind scoured, blowouts and/or depositional areas:
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Amount of litter movement (describe size and distance expected to travel):
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Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
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Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
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Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
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Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
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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:
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Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
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Average percent litter cover (%) and depth ( in):
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Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
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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:
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Perennial plant reproductive capability:
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