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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): 040X–Sonoran Basin and Range
AZ 40.3 – Colorado Sonoran Desert
Elevations range from 300 to 1200 feet and precipitation averages 3 to 7 inches per year. Vegetation includes creosotebush, white bursage, brittlebush, Mormon tea, teddybear cholla, elephant tree, smoke tree, ocotillo, and big galleta. The soil temperature regime is hyperthermic and the soil moisture regime is typic aridic. This unit occurs within the Basin and Range Physiographic Province and is characterized by numerous mountain ranges that rise abruptly from broad, plain-like valleys and basins. Igneous and metamorphic rock classes dominate the mountain ranges and sediments filling the basins represent combinations of fluvial, lacustrine, colluvial and alluvial deposits.Table 1. Dominant plant species
Tree Not specified
Shrub (1) Ambrosia dumosa
(2) Larrea tridentata var. tridentataHerbaceous (1) Pleuraphis rigida
(2) Muhlenbergia porteriPhysiographic features
This range site occurs on recently blown sand dunes, mesas and alluvial fans. The Rositas soils receive no runoff from the surrounding areas, and it does not suffer from excessive loss from runoff. The Vint soils benefit greatly from run-in moisture from surrounding areas, however, they do not suffer from excessive runoff.
Table 2. Representative physiographic features
Landforms (1) Dune
(2) Mesa
(3) Alluvial fan
Elevation 75 – 1000 ft Slope 0 – 15 % Aspect Aspect is not a significant factor Climatic features
Precipitation in this common resource area ranges from 3-7 inches yearly. Despite historical averages in rainfall amounts, as one moves from east to west in this resource area rains become more unpredictable and variable with Coefficients of Variation of annual rainfall equal to 44% at Gila Bend and 65% at Mohawk. Winter-Summer rainfall ratios are 40-60%. Summer rains fall July-September, originate in the Gulf of Mexico and are convective, usually brief intense thunderstorms. Summer thunderstorms usually form over the mountains in the afternoon and spread to the valleys and plains in the evening. The intensity of this precipitation is moderate to heavy, but rarely lasts more than half an hour. Many times these storms produce little more than gusty winds and light showers. Cool season moisture tends to be frontal, originate in the Pacific and Gulf of California and falls in widespread storms with long duration and low intensity. Snow is very rare and falls normally only in the higher mountains.
Mean temperatures for the hottest month (Jul) is 93 F; the coldest month (Jan) is 53 F. Extreme temperatures of 125 F and 10 F have been recorded. Long periods with little or no effective moisture occur frequently.
The winter-spring precipitation is the most dependable on the site. Perennial grasses, though classed as warm season growers, grow actively year-round when moisture is available. Shrubs and trees generally respond to seasonal moisture. The two rainy periods bring about their respective production of either winter or summer annual grasses and forbs.Table 3 Representative climatic features
Frost-free period (average) 360 days Freeze-free period (average) 0 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 that are grouped together on this site are deep to bedrock or other plant root restricting layers. The surface soil textures range in depth of 8-12 inches, with textures from sand to loamy fine sand. The underlying layers have moderately rapid or rapid permeability, but can absorb and hold all the moisture climate supplies. Soluble salt accumulations are low and pH ranges from 7.9-8.4. With good begetative cover, infiltration rates are high. The soil blowing hazard is severe and plant-soil moisture relationships are fair. Percent coarse fragments average less than 15% of the total soil volume. Soils mapped on this site include: in SSA-645 Aguila-Carefree area MU Carrizo-14; SSA-649 Yuma-Wellton area MU Vint-32; SSA-653 Gila Bend-Ajo area MU Rositas LFS-57; SSA-656 Colorado River Indian Reservation MU's Rositas-29 & Torripsamments-4.
Table 4. Representative soil features
Surface texture (1) Sand
(2) Loamy sand
(3) Loamy fine sand
Family particle size (1) Sandy
Drainage class Well drained Permeability class Very rapid Soil depth 60 in Surface fragment cover <=3" 0 – 15 % Surface fragment cover >3" Not specified Available water capacity
(0-40in)3.6 – 4.8 in Calcium carbonate equivalent
(0-40in)0 – 3 % Electrical conductivity
(0-40in)Not specified Sodium adsorption ratio
(0-40in)Not specified Soil reaction (1:1 water)
(0-40in)7.4 – 8.4 Subsurface fragment volume <=3"
(Depth not specified)Not specified Subsurface fragment volume >3"
(Depth not specified)Not specified 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 fire, grazing, 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 amount shown for each group. Divide the resulting total by the total normal year production shown in the plant community description. If the 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
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Click on state and transition labels to scroll to the respective textEcosystem states
State 1 submodel, plant communities
State 1
Historic Climax Plant CommunityCommunity 1.1
Historic Climax Plant CommunityThis range site has a plant community made up of a mixture of perennial and annual grasses, forbs and desert shrubs.
Plant species most likely to invade or increase on this site following disturbance are creosotebush, white bursage, and primrose. Continuous livestock grazing use will decrease perennial grasses, which are replaced by lower forage value shrubs and forbs.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 360 405 450 Shrub/Vine 120 150 180 Forb 6 18 30 Total 486 573 660 Figure 5. Plant community growth curve (percent production by month). AZ4041 , 40.3 3-7" p.z. all sites. Most growth occurs in the winter to early spring, plants are dormant May through October..
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 20 40 25 0 0 0 0 0 0 5 5 Additional community tables
Table 6. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike0 Dominant Perennial Grass 330–390 big galleta PLRI3 Pleuraphis rigida 330–390 – 1 Misc. Perennial Grasses 30–60 California threeawn ARCA9 Aristida californica 14–29 – threeawn ARIST Aristida 14–29 – bush muhly MUPO2 Muhlenbergia porteri 14–29 – desert panicgrass PAUR Panicum urvilleanum 14–29 – sand dropseed SPCR Sporobolus cryptandrus 14–29 – mesa dropseed SPFL2 Sporobolus flexuosus 14–29 – 2 Annual Grasses 6–18 sixweeks threeawn ARAD Aristida adscensionis 3–9 – needle grama BOAR Bouteloua aristidoides 3–9 – sixweeks grama BOBA2 Bouteloua barbata 3–9 – purple fleabane ERPU3 Erigeron purpuratus 3–9 – littleseed muhly MUMI Muhlenbergia microsperma 3–9 – Bigelow's bluegrass POBI Poa bigelovii 3–9 – sixweeks fescue VUOC Vulpia octoflora 3–9 – Forb3 Misc. Forbs 6–30 desert sand verbena ABVI Abronia villosa 0–1 – onyxflower ACCO3 Achyronychia cooperi 0–1 – common fiddleneck AMMEI2 Amsinckia menziesii var. intermedia 0–1 – bristly fiddleneck AMTE3 Amsinckia tessellata 0–1 – New Mexico silverbush ARNE2 Argythamnia neomexicana 0–1 – Cedros milkvetch ASIN6 Astragalus insularis 0–1 – desert marigold BAMU Baileya multiradiata 0–1 – spiderling BOERH2 Boerhavia 0–1 – Booth's suncup CABOB Camissonia boothii ssp. boothii 0–1 – brittle spineflower CHBR Chorizanthe brevicornu 0–1 – Esteve's pincushion CHST Chaenactis stevioides 0–1 – Panamint cryptantha CRAN4 Cryptantha angustifolia 0–1 – redroot cryptantha CRMI Cryptantha micrantha 0–1 – wingnut cryptantha CRPT Cryptantha pterocarya 0–1 – soft prairie clover DAMO2 Dalea mollissima 0–1 – California shieldpod DICA7 Dithyrea californica 0–1 – miniature woollystar ERDI2 Eriastrum diffusum 0–1 – desert trumpet ERIN4 Eriogonum inflatum 0–1 – kidneyleaf buckwheat ERRE3 Eriogonum reniforme 0–1 – Thomas' buckwheat ERTH Eriogonum thomasii 0–1 – little deserttrumpet ERTR8 Eriogonum trichopes 0–1 – California poppy ESCAM Eschscholzia californica ssp. mexicana 0–1 – spurge EUPHO Euphorbia 0–1 – desert lily HEUN2 Hesperocallis undulata 0–1 – Great Basin langloisia LASE3 Langloisia setosissima 0–1 – shaggyfruit pepperweed LELA Lepidium lasiocarpum 0–1 – Bigelow's linanthus LIBI2 Linanthus bigelovii 0–1 – foothill deervetch LOHU2 Lotus humistratus 0–1 – strigose bird's-foot trefoil LOSTT Lotus strigosus var. tomentellus 0–1 – bajada lupine LUCO Lupinus concinnus 0–1 – California desertdandelion MACA6 Malacothrix californica 0–1 – yellowcomet MEAF2 Mentzelia affinis 0–1 – whitestem blazingstar MEAL6 Mentzelia albicaulis 0–1 – cottonheads NEDE Nemacaulis denudata 0–1 – glandular threadplant NEGL Nemacladus glanduliferus 0–1 – birdcage evening primrose OEDE2 Oenothera deltoides 0–1 – desert evening primrose OEPR Oenothera primiveris 0–1 – giant Spanish needle PAARG Palafoxia arida var. gigantea 0–1 – chuckwalla combseed PEHE Pectocarya heterocarpa 0–1 – broadfruit combseed PEPL Pectocarya platycarpa 0–1 – desert Indianwheat PLOV Plantago ovata 0–1 – desert unicorn-plant PRAL4 Proboscidea althaeifolia 0–1 – New Mexico plumeseed RANE Rafinesquia neomexicana 0–1 – desert globemallow SPAM2 Sphaeralcea ambigua 0–1 – Coulter's globemallow SPCO2 Sphaeralcea coulteri 0–1 – small wirelettuce STEX Stephanomeria exigua 0–1 – longbeak streptanthella STLO4 Streptanthella longirostris 0–1 – Shrub/Vine4 Dominant Shrub 90–120 burrobush AMDU2 Ambrosia dumosa 90–120 – 5 Misc. Shrubs 30–60 triangle bur ragweed AMDE4 Ambrosia deltoidea 3–6 – California croton CRCA5 Croton californicus 3–6 – longleaf jointfir EPTR Ephedra trifurca 3–6 – ocotillo FOSP2 Fouquieria splendens 3–6 – littleleaf ratany KRER Krameria erecta 3–6 – white ratany KRGR Krameria grayi 3–6 – creosote bush LATRT Larrea tridentata var. tridentata 3–6 – honey mesquite PRGL2 Prosopis glandulosa 3–6 – dyebush PSEM Psorothamnus emoryi 3–6 – lotebush ZIOBO Ziziphus obtusifolia var. obtusifolia 3–6 – 6 Succulents 6–12 buckhorn cholla CYACA2 Cylindropuntia acanthocarpa var. acanthocarpa 1–3 – Wiggins' cholla CYEC3 Cylindropuntia echinocarpa 1–3 – branched pencil cholla CYRA9 Cylindropuntia ramosissima 1–3 – Engelmann's hedgehog cactus ECEN Echinocereus engelmannii 1–3 – California barrel cactus FECYC Ferocactus cylindraceus var. cylindraceus 1–3 – Interpretations
Animal community
This site produces year-round forage and is easily traversed by all classes of cattle. As these soils are very susceptible to wind and water erosion, management that maintains the plant cover is most important. Fencing and water development may be important in achieving grazing control.
This site has good diversity in the potential plant community, however, grasses dominate the general aspect. The site is primarily transitory for large mammals. Burrowing rodents are numerous and raptors, the predatory mammals, use the site frequently as a feeding area. Free water is totally lacking on the site.Recreational uses
This site occurs as level, hummocky or low dune uplands, along drainageways and throughout the desert plains. In years with average or better winter precipitation, forbs such as sand verbena and dune primrose lend much color to the site and provide good contrast to the grassy appearance. This is perhaps the most showy site in the desert when good winter moisture is received. Very few days in the fall, winter or spring are too uncomfortable to enjoy outdoor activities. In Jun-Aug, however, the afternoon hear restricts activity. Horseback riding, wildlife observation, hunting, hiking and photography are the main activities suited for this site.
Supporting information
Type locality
Location 1: La Paz County, AZ Township/Range/Section T8N R17W S23 General legal description Nine Mile Allotment, Cactus Plain S23, R17W, T8N - La Paz county Nine Mile Allotment, La Rosa Plain, S34, R19W, T7N - La Paz county Sentinel Allotment S16, R10W, T7S - Maricopa county. Contributors
Larry D. Ellicott
Steve BarkerRangeland 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 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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