Natural Resources
Conservation Service
Ecological site R030XA102AZ
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3-6" p.z.
Last updated: 10/21/2024
Accessed: 08/21/2026
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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): 030X–Mojave Basin and Range
This unit occurs within the Basin and Range Province and is characterized by broad basins, valleys, and old lakebeds. Widely spaced mountains trending north to south occur throughout the area. Isolated, short mountain ranges are separated by an aggraded desert plain. The mountains are fault blocks that have been tilted up. Long alluvial fans coalesce with dry lakebeds between some of the ranges.
LRU notes
AZ LRU 30-1 – Lower Mohave Desert
Elevations range from 400 to 2500 feet and precipitation averages 3 to 6 inches per year. Vegetation includes creosotebush, white bursage, Mormon tea, and brittlebush. The soil temperature regime is hyperthermic and the soil moisture regime is typic aridic.Ecological site concept
This ecological site is located on steep slopes of terraces adjacent to the Colorado River. Soils are moderately deep to deep.
Table 1. Dominant plant species
Tree Not specified
Shrub (1) Larrea tridentata
Herbaceous Not specified
Physiographic features
This range site occurs on terraces adjacent to the Colorado River. It does not receive run-in from adjacent areas, but suffers from excessive loss from runoff. It occurs on all exposures.
Table 2. Representative physiographic features
Landforms (1) Hill
(2) Mountain
Flooding frequency None Ponding frequency None Elevation 800 – 2000 ft Slope 0 – 50 % Climatic features
The 30-1AZ Lower Mohave Desert Shrub land resource unit is characterized by a hot, dry climate. The average annual rainfall is 3 to 6 inches, but it can be extremely variable (e.g. from 0 to 11 inches). There can be long periods when little or no precipitation is received. Most of the precipitation for the year could arrive in just a couple of storms. The soil moisture regime is typic aridic and the soil temperature regime is hyperthermic. Winter precipitation from November through April occurs as gentle rains from storms coming out of the Pacific Ocean. Snow is very rare and only falls in the highest mountains. A seasonal drought occurs in May and June. Summer/fall precipitation from July through October comes from spotty, unreliable, and sometimes violent thunderstorms. The moisture originates in the Gulf of Mexico (and the Pacific Ocean in the fall) and flows into the state on the north end of the Mexican monsoon. Strong winds are common, especially during the spring.
Table 3 Representative climatic features
Frost-free period (average) 330 days Freeze-free period (average) 370 days Precipitation total (average) 10 in BarLineFigure 2. Monthly precipitation range
BarLineFigure 3. Monthly average minimum and maximum temperature
">Influencing water features
Soil features
Soils on this site are deep. Surface depth is highly variable, ranging from 1 to 60 inches. Texture ranges from sand to clay. Underlying layers have permeability ranging from rapid to slow; this soil cannot hold climate supplied moisture. Soluble salt accumulations are low. pH ranges from 7.8-8.4. With good vegetative cover infiltration rate is low. Stability against erosion processes is poor. Plant-soil moisture relationships are poor. Gravel content in certain horizon average greater than 35%. The torriorthents contain greater than 35% gravels by volume.
Table 4. Representative soil features
Surface texture (1) Gravelly sand
(2) Sandy clay loam
(3) Clay loam
Drainage class Well drained to somewhat excessively drained Permeability class Moderate to very rapid Soil depth 1 – 60 in Soil reaction (1:1 water)
(0-40in)7.8 – 8.4 Ecological dynamics
The dominant aspect of this ecological site is desert shrubs with a sparse stand of perennial grasses. Limited natural disturbance occurs on this site. Steep slopes and limited available forage restrict livestock impacts on this site. Annual forbs flourish in springs, particularly following wet winters; the green forage produced is desired by livestock but is largely unused once matured. Non-native annuals are well adapted on this site.
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 2 submodel, plant communities
State 1
Historic Climax Plant CommunityCommunity 1.1
Historic Climax Plant CommunityThe plant community on this site is predominantly desert shrubs and trees. Perennial grasses present are very drought hardy and make up a small percentage of the community. This site produces very little usable forage; however, being adjacent to bottom sites, it is usually found in less than good contition. Continued use results in a loss of perennial grasses and forbs, and an increase in woody plants.
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 175 192 212 Forb 12 25 50 Grass/Grasslike 12 33 25 Total 199 250 287 Figure 5. Plant community growth curve (percent production by month). AZ3011 , 30.1 3-6" p.z. all sites. Growth begins in late winter, most growth occurs in the spring..
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 7 30 32 13 7 3 5 2 1 0 0 State 2
Historic Native Plant Community plus Introduced AnnualsCommunity 2.1
Non-native AnnualsThis plant community resembles the historic native plant community, but exotic annuals have been introduced. Non-native species include red brome, Mediterranean grass (Schismus spp.), and filaree. The flourish of non-native annuals that occurs following rainfalls may preclude native annuals.
Transition T1A
State 1 to 2Introduction of non-native annual grass and forb seed.
Restoration pathway R2A
State 2 to 1None known.
Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 2–12 threeawn ARIST Aristida 2–6 – bush muhly MUPO2 Muhlenbergia porteri 2–6 – big galleta PLRI3 Pleuraphis rigida 2–6 – 2 2–12 Grass, annual 2GA Grass, annual 2–12 – Forb3 12–50 Forb, annual 2FA Forb, annual 12–25 – Forb, perennial 2FP Forb, perennial 12–25 – devil's spineflower CHRI Chorizanthe rigida 12–25 – Shrub/Vine4 25–50 creosote bush LATR2 Larrea tridentata 25–50 – 5 12–38 triangle bur ragweed AMDE4 Ambrosia deltoidea 12–38 – 6 0–12 yellow paloverde PAMI5 Parkinsonia microphylla 0–12 – 7 88–112 burrobush AMDU2 Ambrosia dumosa 0–56 – Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 0–56 – longleaf jointfir EPTR Ephedra trifurca 0–56 – white ratany KRGR Krameria grayi 0–56 – desert-thorn LYCIU Lycium 0–56 – smoketree PSSP3 Psorothamnus spinosus 0–56 – Table 7. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Other information
Kingman, Phoenix, & Fredonia field offices.
Supporting information
Contributors
Larry D. Ellicott
Steve Barker
UnknownApproval
Kendra Moseley, 10/21/2024
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 08/21/2026 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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