Natural Resources
Conservation Service
Ecological site R030XA103AZ
Clayey Bottom 3-6" p.z.
Last updated: 2/18/2025
Accessed: 03/17/2025
General information
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.
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 occurs in bottoms. Soil texture ranges from clay to clay loam. The soil is non-skeletal.
Table 1. Dominant plant species
| Tree |
(1) Prosopis glandulosa |
|---|---|
| Shrub |
(1) Acacia greggii |
| Herbaceous |
(1) Pleuraphis mutica |
Physiographic features
This site occurs in a bottom position and benefits significantly from moisture run-in from adjacent areas. It occurs on all exposures.
Table 2. Representative physiographic features
| Landforms |
(1)
Stream terrace
(2) Flood plain |
|---|---|
| Flooding duration | Extremely brief (0.1 to 4 hours) to very brief (4 to 48 hours) |
| Flooding frequency | Rare to occasional |
| Ponding duration | Very brief (4 to 48 hours) to brief (2 to 7 days) |
| Ponding frequency | None to rare |
| Elevation | 500 – 2,000 ft |
| Slope | 1% |
| Aspect | Aspect is not a significant factor |
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) | 325 days |
|---|---|
| Freeze-free period (average) | 365 days |
| Precipitation total (average) | 6 in |
Figure 1. Monthly average minimum and maximum temperature
Influencing water features
Soil features
Soils on this site are deep. Surface soil ranges from 4-10 inches deep and ranges in texture from silty clay loam to clay. Subsoil may have a permeability ranging from slow to moderately slow, but can absorb and hold all climate supplied moisture. Soluble salt accumulations are low. pH ranges from 7.9-8.4. With good vegetative cover, infiltration rates are moderate. Stability against erosion processes are moderate and plant-soil moisture relationships are average. Less than 15% course fragments occur in the soil profile.
A typical soil profile is:
Ap-0 to 12 inches; clay
C1-12 to 28 inches; clay
2C2-28 to 60 inches; stratified sand
Table 4. Representative soil features
| Surface texture |
(1) Silty clay loam (2) Clay loam |
|---|---|
| Family particle size |
(1) Clayey |
| Drainage class | Well drained |
| Permeability class | Slow to moderately slow |
| Soil depth | 60 in |
| Surface fragment cover <=3" | Not specified |
| Surface fragment cover >3" | Not specified |
| Electrical conductivity (0-40in) |
1 – 8 mmhos/cm |
| Sodium adsorption ratio (0-40in) |
3 |
| Soil reaction (1:1 water) (0-40in) |
7.9 – 8.4 |
| Subsurface fragment volume <=3" (Depth not specified) |
15% |
| Subsurface fragment volume >3" (Depth not specified) |
Not specified |
Ecological dynamics
Clayey Bottom, 3"-6" p.z., ecological site is located on swales at the lower end of alluvial fans and floodplains along the washes and major drainageways. The potential plant community is a shrub-grass dominated bottomland. Natural disturbances are few; natural fire may play a role in maintaining shrub-grass balance. Continuous livestock grazing will impact this site by removing fire fuel load and depleting perennial grass cover. Non-native annual forbs and grasses may flourish on this site following rainfall.
State and transition model
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Ecosystem states
State 1 submodel, plant communities
State 2 submodel, plant communities
State 1
Historic Climax Plant Community
Community 1.1
Historic Climax Plant Community
The plant community of this ecological has an overstory vegetation of catclaw, mesquite and cactus, with an understory of annual and perennial grasses and forbs.
Figure 2. 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 | 240 | 255 | 280 |
| Shrub/Vine | 80 | 110 | 140 |
| Forb | 20 | 35 | 60 |
| Total | 340 | 400 | 480 |
Figure 3. 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
Catclaw-Mesquite
Community 2.1
Catclaw-Mesquite
Perennial grass canopy cover is reduced to largely absent. Shrub density and cover increases. Native and non-native annual forbs and grasses dominate the plant community. Remnant tobosa will not be able to re-colonize large areas because it is a poor producer of viable seed; removal of grazing pressure will allow existing tobosa to establish colony patches.
Transition T1A
State 1 to 2
Yearlong livestock grazing, introduction of non-native annual forb and grass seed.
Restoration pathway R2A
State 2 to 1
None known.
Additional community tables
Table 6. Community 1.1 plant community composition
| Group | Common name | Symbol | Scientific name | Annual production (lb/acre) | Foliar cover (%) | |
|---|---|---|---|---|---|---|
|
Grass/Grasslike
|
||||||
| 1 | 140–200 | |||||
| tobosagrass | PLMU3 | Pleuraphis mutica | 140–200 | – | ||
| 2 | 20–60 | |||||
| threeawn | ARIST | Aristida | 20–60 | – | ||
| 3 | 4–20 | |||||
| low woollygrass | DAPU7 | Dasyochloa pulchella | 4–20 | – | ||
| 4 | 4–20 | |||||
| sixweeks fescue | VUOC | Vulpia octoflora | 4–20 | – | ||
| 5 | 4–20 | |||||
| sixweeks grama | BOBA2 | Bouteloua barbata | 4–20 | – | ||
| 6 | 4–20 | |||||
| Bigelow's bluegrass | POBI | Poa bigelovii | 4–20 | – | ||
|
Forb
|
||||||
| 7 | 0–20 | |||||
| plantain | PLANT | Plantago | 0–20 | – | ||
| 8 | 0–20 | |||||
| Emory's globemallow | SPEM | Sphaeralcea emoryi | 0–20 | – | ||
| 9 | 0–20 | |||||
| Coulter's globemallow | SPCO2 | Sphaeralcea coulteri | 0–20 | – | ||
| 10 | 20–40 | |||||
| Forb, annual | 2FA | Forb, annual | 20–40 | – | ||
|
Shrub/Vine
|
||||||
| 11 | 20–60 | |||||
| catclaw acacia | ACGR | Acacia greggii | 20–60 | – | ||
| 12 | 20–40 | |||||
| honey mesquite | PRGL2 | Prosopis glandulosa | 20–40 | – | ||
| 13 | 4–20 | |||||
| yellow paloverde | PAMI5 | Parkinsonia microphylla | 4–20 | – | ||
| 14 | 0–12 | |||||
| pricklypear | OPUNT | Opuntia | 0–12 | – | ||
| 15 | 0–12 | |||||
| Arizona pencil cholla | CYAR14 | Cylindropuntia arbuscula | 0–12 | – | ||
| 16 | 0–12 | |||||
| desert-thorn | LYCIU | Lycium | 0–12 | – | ||
Interpretations
Supporting information
Contributors
Larry D. Ellicott`
Steve Barker
Unknown
Approval
Kendra Moseley, 2/18/2025
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 | 02/20/2025 |
| Approved by | Kendra Moseley |
| Approval date | |
| Composition (Indicators 10 and 12) based on | Annual Production |
Indicators
-
Number and extent of rills:
-
Presence of water flow patterns:
-
Number and height of erosional pedestals or terracettes:
-
Bare ground from Ecological Site Description or other studies (rock, litter, lichen, moss, plant canopy are not bare ground):
-
Number of gullies and erosion associated with gullies:
-
Extent of wind scoured, blowouts and/or depositional areas:
-
Amount of litter movement (describe size and distance expected to travel):
-
Soil surface (top few mm) resistance to erosion (stability values are averages - most sites will show a range of values):
-
Soil surface structure and SOM content (include type of structure and A-horizon color and thickness):
-
Effect of community phase composition (relative proportion of different functional groups) and spatial distribution on infiltration and runoff:
-
Presence and thickness of compaction layer (usually none; describe soil profile features which may be mistaken for compaction on this site):
-
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:
-
Amount of plant mortality and decadence (include which functional groups are expected to show mortality or decadence):
-
Average percent litter cover (%) and depth ( in):
-
Expected annual annual-production (this is TOTAL above-ground annual-production, not just forage annual-production):
-
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:
-
Perennial plant reproductive capability:
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