Natural Resources
Conservation Service
Ecological site R030XA110AZ
Loamy Bottom 3-6" p.z.
Last updated: 2/18/2025
Accessed: 05/11/2025
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 is located in bottom position and receives additional moisture from run-on. Surface soils of loam, fine sandy loam, or silt loam are 4 to 8 inches thick.
Table 1. Dominant plant species
| Tree |
Not specified |
|---|---|
| Shrub |
Not specified |
| Herbaceous |
(1) Pleuraphis rigida |
Physiographic features
This range site occurs in a bottom position. It benefits significantly from run-in moisture from adjacent areas and suffers from approximately the same loss from runoff. It occurs on all exposures on recent alluvial fans and drainage ways.
Table 2. Representative physiographic features
| Landforms |
(1)
Alluvial fan
(2) Drainageway |
|---|---|
| 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 | 600 – 2,500 ft |
| Slope | 3% |
| 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
The soils characterizing this site are deep. Surface soil ranges from 4-8 inches deep with a texture of loam, fine sandy loam or silt loam. Soluble salt accumulations are low and pH ranges from 7.9-8.4. With good vegetative cover, infiltration rates are high. Stability against erosion processes is poor; plant-soil moisture relationships are moderate. Gravel may occur throughout the soil, but is generally less than 15% of the total soil volume.
A typical soil profile is:
Ap-0 to 13 inches; loam; slightly effervescent
C1-13 to 28 inches; sstratified very fine sandy loam; strongly effervescent
C2-28 to 60 inches; stratified very fine sandy loam; strongly effervescent
Table 4. Representative soil features
| Surface texture |
(1) Loam (2) Loamy fine sand (3) Loamy sand |
|---|---|
| Family particle size |
(1) Loamy |
| Drainage class | Well drained to moderately well drained |
| Permeability class | Moderate to rapid |
| Soil depth | 60 in |
| Surface fragment cover <=3" | Not specified |
| Surface fragment cover >3" | Not specified |
| 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
This site is located on large swales, flats in canyon bottoms, components of large desert plains, and loamy flood plains of drainage ways. It is open grassland with scattered trees and shrubs. In good winter precipitation years, spring wildflowers lend color to the areas. Yearlong livestock grazing will deplete the perennial grass community, allowing shrubs to increase in density and size.
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 text
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 is a mixture of perennial grasses and forbs, annual grasses and forbs, and scattered shrubs. This site is favored by livestock due to accessibility, longer grean period, and nearness to water. When plant cover is depleted, the site is very susceptible to sheet and gully erosion and woody plant increase, notabley mesquite and creosotebush. When gullied, much of the area once flooded in a loamy bottom no longer receives this extra moisture.
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 | 250 | 335 | 350 |
| Shrub/Vine | 75 | 120 | 125 |
| Forb | 25 | 40 | 50 |
| Total | 350 | 495 | 525 |
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
Shrubland
Community 2.1
Catclaw-Mesquite
Perennial grass canopy cover is reduced and largely absent. Shrub density and cover has increased. Native and non-native annual forbs and grasses dominate the plant community following rainfall. Remnant perennial grasses will not be able to re-colonize; removal of grazing pressure will allow existing perennial grasses to regain vigor. Non-native annual grasses and forbs like; red brome, cheatgrass, kochia, tumble pigweed, russian thistle, tumble mustard, yellow starthistle, wild oats and filaree, can invade and dominate areas of the site with very low tobosa cover. Perennial forbs like russian knapweed and leafy spurge could invade and, perhaps, dominate this site. These species can, over time, reduce the seed-bank of native annual grasses and forbs.
Transition T1A
State 1 to 2
Long-term yearlong livestock grazing and 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 | 175–250 | |||||
| big galleta | PLRI3 | Pleuraphis rigida | 175–250 | – | ||
| 2 | 5–50 | |||||
| bush muhly | MUPO2 | Muhlenbergia porteri | 5–50 | – | ||
| 3 | 5–50 | |||||
| threeawn | ARIST | Aristida | 5–50 | – | ||
| 4 | Annual Grasses | 25–75 | ||||
| threeawn | ARIST | Aristida | 5–25 | – | ||
| needle grama | BOAR | Bouteloua aristidoides | 5–25 | – | ||
| sixweeks grama | BOBA2 | Bouteloua barbata | 5–25 | – | ||
| muhly | MUHLE | Muhlenbergia | 5–25 | – | ||
| sixweeks fescue | VUOC | Vulpia octoflora | 5–25 | – | ||
|
Forb
|
||||||
| 5 | 25–50 | |||||
| Forb, annual | 2FA | Forb, annual | 0–25 | – | ||
| pepperweed | LEPID | Lepidium | 0–25 | – | ||
| plantain | PLANT | Plantago | 0–25 | – | ||
| desert globemallow | SPAM2 | Sphaeralcea ambigua | 0–25 | – | ||
| Coulter's globemallow | SPCO2 | Sphaeralcea coulteri | 0–25 | – | ||
|
Shrub/Vine
|
||||||
| 6 | 25–100 | |||||
| whitethorn acacia | ACCO2 | Acacia constricta | 5–25 | – | ||
| catclaw acacia | ACGR | Acacia greggii | 5–25 | – | ||
| crucifixion thorn | CAEM4 | Castela emoryi | 5–25 | – | ||
| desert-thorn | LYCIU | Lycium | 5–25 | – | ||
| desert ironwood | OLTE | Olneya tesota | 5–25 | – | ||
| honey mesquite | PRGL2 | Prosopis glandulosa | 5–25 | – | ||
| lotebush | ZIOB | Ziziphus obtusifolia | 5–25 | – | ||
| 7 | 5–25 | |||||
| Engelmann's hedgehog cactus | ECEN | Echinocereus engelmannii | 0–10 | – | ||
| candy barrelcactus | FEWI | Ferocactus wislizeni | 0–10 | – | ||
| cactus apple | OPEN3 | Opuntia engelmannii | 0–10 | – | ||
Interpretations
Supporting information
Contributors
Larry D. Ellicott
SB
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:
Print Options
Sections
Font
Other
The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.
Click on box and path labels to scroll to the respective text.