Natural Resources
Conservation Service
Ecological site R040XA125AZ
Sandy Bottom, Woodland
10"-13" p.z.
Last updated: 10/17/2024
Accessed: 09/10/2026
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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.
MLRA notes
Major Land Resource Area (MLRA): 040X–Sonoran Basin and Range
Major Land Resource Area (MLRA) 40 is the portion of Sonoran Desert that extends from northwest Mexico into southwestern Arizona and southeastern California. This MLRA is hot desert characterized by bimodal precipitation coupled with hot summers and mild winters. These conditions give rise to a rich biological diversity visually dominated by columnar cactus (saguaro) and leguminous trees (palo verde). 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 basin sediments are combinations of fluvial, lacustrine, colluvial and alluvial deposits.
LRU notes
Land Resource Unit (LRU) 40-1, Upper Sonoran Desert, is characterized by desert scrub vegetation with no desert pavement present. Trees grow on uplands as well as in washes and on hillslopes. Elevations range from 2000 to 3800 feet, and precipitation averages 10 to 13 inches per year. Vegetation includes saguaro, palo verde, mesquite, creosotebush, triangle bursage, prickly pear, cholla, limberbush, wolfberry, bush muhly, threeawns, ocotillo, and globe mallow. The soil temperature regime is thermic and the soil moisture regime is typic aridic.
Classification relationships
USDA-NRCS Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin: Western Range and Irrigated Region D Major Land Resource Area 40 - Sonoran Basin and Range Land Resource Unit 1 - Upper Sonoran Desert Ecological Site Sandy Bottom, Woodland, 10"-13" p.z.
U.S. Environmental Protection Agency, Ecological Regions of North America: Level I, Region 10 North American Deserts Level II, 10.2 Warm Deserts Level III, Ecoregion 81, Sonoran Basin and Range Level IV, 81l, 81n, 81o
USDA-USFS Ecological Subregions: Sections of the Conterminous United States Section 322 American Semidesert and Desert Province Section 322B, Sonoran DesertEcological site concept
Sandy Bottom, Woodland, 10”–13” p.z. occurs on a bottom position, receiving both rainfall and run-on moisture. The shallow water table fluctuates in depth but is available to the plant community year-round. Soils have visible redoximorphic features with 80" of surface. Reference plant community is dominated by tall trees with a diverse understory. Obligate and facultative wetland plants occur along reaches of surface or near surface water flow. Aspect is a gallery woodland.
Associated sites
R040XA124AZ Loamy Bottom, Woodland 10"-13" p.z.
adjacent stream terraces, no soil redox features
R040XA115AZ Sandy Wash 10"-13" p.z.
stream channel with ephemeral water flows, no soil redox features
Similar sites
F040XB215AZ Sandy Bottom, Woodland 7" - 10" p.z.
Elevations 1,200' to 2,000'
F040XC327AZ Sandy Bottom, Woodland 3"-7" p.z.
Elevations 300' to 1,200'
Table 1. Dominant plant species
Tree (1) Populus fremontii
(2) Salix gooddingiiShrub Not specified
Herbaceous (1) Sporobolus wrightii
Physiographic features
This site occurs on floodplains, low stream terraces and in channels of major drainageways and first and second order tributaries. The site experiences regular overbank flood events, and has a shallow water table, ranging from 3 to 10 feet in depth. Slopes range from 0% to 2%, and elevations range from 2200 to 3600 feet.
Table 2. Representative physiographic features
Landforms (1) Flood plain
(2) Stream terrace
(3) Channel
Elevation 2200 – 3600 ft Slope 0 – 2 % Climatic features
Annual precipitation ranges from 10 to 13 inches in the southern part of this LRU, with elevations between 1900 and 3200 feet. Annual precipitation in the northern part ranges from 11 to 14 inches, with elevations between 2000 and 3800 feet. Rainfall ratios range from 40:60 (winter:summer) in the southern part, 50:50 in the central portion, and 60:40 in the northern part.
Overall, average annual rainfall is variable, but increases in variability from east to west across the region. For long-term precipitation data, the coefficient of variation, the ratio of the standard deviation to the mean expressed as a percentage, increases from 29% at Tucson (east) to 36% at Carefree (west).
Rainfall intensity differs between rainfall seasons. Winter frontal storms develop in the Pacific Ocean and Gulf of California, producing widespread, low-intensity and long duration precipitation events. Snowfall is rare and seldom last for more than a few hours. During summer months (July-September), atmospheric activity in the Gulf of Mexico produces convective thunderstorms of short duration, usually less than 30 minutes, but of moderate to heavy intensity. May and June are the driest months of the year. Humidity is generally very low.
Winter temperatures are mild, with only a few days of freezing temperatures overnight. Summer temperatures are warm to hot, with several days in June and July exceeding 105°F.
Spring and the summer growing seasons are equally important for perennial grass, forb and shrub growth. With above average precipitation, cool and warm season annual forbs and grasses can be common in their respective seasons. Perennial forage species can remain green throughout the year with sufficient available moisture.">Influencing water features
Soil features
These are very young soils on sandy and gravelly alluvium of mixed origin. Soils are deep and have excellent plant-soil moisture relationships due to shallow water tables.
Table 3. Representative soil features
Surface texture (1) Gravelly sandy loam
(2) Loamy fine sand
(3) Fine sandy loam
Family particle size (1) Sandy
Drainage class Somewhat excessively drained to well drained Permeability class Rapid to moderately rapid Soil depth 60 – 0 in Surface fragment cover <=3" 0 – 30 % Surface fragment cover >3" 0 – 10 % Available water capacity
(0-40in)2.5 – 4.2 in Calcium carbonate equivalent
(0-40in)0 – 3 % Electrical conductivity
(0-40in)0 – 2 mmhos/cm Sodium adsorption ratio
(0-40in)0 – 2 Soil reaction (1:1 water)
(0-40in)7 – 7.8 Subsurface fragment volume <=3"
(Depth not specified)0 – 65 % Subsurface fragment volume >3"
(Depth not specified)0 – 20 % Ecological dynamics
Sandy Bottom, Woodland, 10-13" p.z. is a gallery woodland associated with large perennial water courses. Dominated by cottonwood and willow, the site is vulnerable to invasion from saltcedar.
State and transition model
Custom diagramStandard diagram
Figure 1. Sandy Bottom, Woodland STM
Figure 2. Sandy bottom, woodland, 10-13" p.z. STM Legend
More interactive model formats are also available. View Interactive Models
More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective textEcosystem states
T1A - Groundwater pumping T1C - Continuous heavy grazing R2A - Cessation of groundwater pumping. T2A - Salt cedar introduction R3A - Unknown R4A - Unknown T4A - Salt cedar introduction State 1 submodel, plant communities
State 2 submodel, plant communities
State 3 submodel, plant communities
State 4 submodel, plant communities
State 1
Gallery Woodland, Native StateCommunity 1.1
Mature Tree Community (Reference)Cottonwood and willow dominated, with 40%-80% canopy cover, with an understory of perennial grasses, sedges, rushes, and wetland forbs.
Figure 3. Annual production by plant type (representative values) or group (midpoint values)
Table 4. Annual production by plant type
Plant type Low
(lb/acre)Representative value
(lb/acre)High
(lb/acre)Grass/Grasslike 750 – 1125 Total 750 – 1125 Community 1.2
Immature Tree CommunityCottonwood and willow occupy between 20%-40% of the canopy cover, with tree saplings occupying 10%-50% of the canopy. Understory of tall grasses, sedges, rushes and wetland forbs. Flood or fire reduce mature tree cover.
State 2
Riverwash StateWide channel, with no streamflow and a lowered water table. Active gully and streambank erosion processes. Native annuals occur on riverwash sands in response to rainfall.
Community 2.1
Riverwash Shrubland CommunityCottonwood and willow occupy 5%-10% of the canopy, with burrobrush and seepwillow also occupying 5%-10% of the canopy.
State 3
Non-Native Woodland StateCottonwood and willow cover eliminated by flood or fire. Saltcedar rapidly colonizes and achieves up to 80% cover. Understory cover reduced to near zero.
Community 3.1
Salt Cedar CommunitySaltcedar occupies from 10%-80% of the canopy. As saltcedar canopy increases, understory decreases or is eliminated.
State 4
Native Tree-Shrub StateMature cottonwood and willow slowly die out, and saplings remain stunted due to grazing pressure. Seepwillow and burrobrush dominate streambanks.
Community 4.1
Seepwillow CommunitySeepwillow and burrobrush dominate streambanks.
Transition T1A
State 1 to 2Water table is lowered to a depth of greater than 20’ by groundwater pumping. Mature trees die back to a level supported by periodic flooding.
Constraints to recovery.Site cannot recover without elimination of groundwater pumping.
Transition T1B
State 1 to 3Saltcedar introduction.
Transition T1C
State 1 to 4Continuous heavy grazing suppresses cottonwood and willow seedling maturation. Old trees die-out.
Restoration pathway R2A
State 2 to 1Cessation of pumping may permit groundwater level to rise with time.
Transition T2A
State 2 to 3Saltcedar introduction.
Restoration pathway R3A
State 3 to 1Unknown.
Restoration pathway R4A
State 4 to 1Unknown.
Transition T4A
State 4 to 3Saltcedar introduction.
Additional community tables
Table 5. Community 1.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Grass/Grasslike1 141–188 saltgrass DISP Distichlis spicata 141–188 – knotgrass PADI6 Paspalum distichum 141–188 – vine mesquite PAOB Panicum obtusum 141–188 – 2 47–94 Havard's threeawn ARHA3 Aristida havardii 47–94 – spidergrass ARTE3 Aristida ternipes 47–94 – cane bluestem BOBA3 Bothriochloa barbinodis 47–94 – sideoats grama BOCU Bouteloua curtipendula 47–94 – Arizona cottontop DICA8 Digitaria californica 47–94 – squirreltail ELELE Elymus elymoides ssp. elymoides 47–94 – green sprangletop LEDU Leptochloa dubia 47–94 – rice cutgrass LEOR Leersia oryzoides 47–94 – mat muhly MURI Muhlenbergia richardsonis 47–94 – whiplash pappusgrass PAVA2 Pappophorum vaginatum 47–94 – plains bristlegrass SEVU2 Setaria vulpiseta 47–94 – spike dropseed SPCO4 Sporobolus contractus 47–94 – sand dropseed SPCR Sporobolus cryptandrus 47–94 – mesa dropseed SPFL2 Sporobolus flexuosus 47–94 – big sacaton SPWR2 Sporobolus wrightii 47–94 – 3 47–94 sedge CAREX Carex 47–94 – flatsedge CYPER Cyperus 47–94 – rush JUNCU Juncus 47–94 – 4 10–94 prairie threeawn AROL Aristida oligantha 10–94 – Rothrock's grama BORO2 Bouteloua rothrockii 10–94 – Arizona brome BRAR4 Bromus arizonicus 10–94 – brome BROMU Bromus 10–94 – feather fingergrass CHVI4 Chloris virgata 10–94 – canyon cupgrass ERLE7 Eriochloa lemmonii 10–94 – pitscale grass HAGR3 Hackelochloa granularis 10–94 – bearded sprangletop LEFUF Leptochloa fusca ssp. fascicularis 10–94 – Mexican sprangletop LEFUU Leptochloa fusca ssp. uninervia 10–94 – mucronate sprangeltop LEPAB Leptochloa panicea ssp. brachiata 10–94 – delicate muhly MUFR Muhlenbergia fragilis 10–94 – witchgrass PACA6 Panicum capillare 10–94 – Arizona signalgrass URAR Urochloa arizonica 10–94 – Forb5 25–125 bigseed alfalfa dodder CUIN Cuscuta indecora 25–125 – mesquite mistletoe PHCA8 Phoradendron californicum 25–125 – oak mistletoe PHLE14 Phoradendron leucarpum 25–125 – Table 6. Community 1.2 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 7. Community 2.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 8. Community 3.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Table 9. Community 4.1 plant community composition
Group Common name Symbol Scientific name Annual production () Foliar cover (%) Interpretations
Animal community
Grazing pressure should be managed to allow for periodic reproduction of Fremont cottonwood and Godding's willow. Cottonwood and willow seeds will germinate on fresh alluvium deposited by spring or summer floods. Seedlings require one full season to outgrow the reach of grazing livestock. Summer seedlings may require two seasons to reach a height where the terminal bud is out of reach. Seedlings of both species are very palatable to cattle.
Wood products
High water tables and very erodible soils limit wood production on this site. The wildlife habitat value of the site is many times greater than the value for any commercial wood products. Wood removal and cutting should be limited to flood damaged and fallen trees and driftwood.
Supporting information
Type locality
Location 1: Maricopa County, AZ Township/Range/Section T7N R4W S20 General legal description Phoenix FO - Hassayampa River Preserve - Nature Conservancy Location 2: Pima County, AZ Township/Range/Section T16S R17E S29 General legal description Tucson FO - Cienaga Creek - Pima County Property Location 3: Gila County, AZ Township/Range/Section T4S R17E S34 General legal description San Carlos FO - Mineral Strip, Deer Creek Location 4: Pima County, AZ Township/Range/Section T6S R16E S17 General legal description Tucson FO - San Pedro River between Dudleyville and Winkleman - NW 1/4 Sec.17 Other references
Griffith, G.E., Omernik, J.M., Johnson, C.B., and Turner, D.S., 2014, Ecoregions of Arizona (poster): U.S. Geological Survey Open-File Report 2014-1141, with map, scale 1:1,325,000, https://dx.doi.org/10.3133/ofr20141141. ISSN 2331-1258 (online)
United States Department of Agriculture, Natural Resources Conservation Service. 2006. Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook 296.Contributors
Dan Robinett, original author
Wilma J Renken, revisionsApproval
Kendra Moseley, 10/17/2024
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 09/10/2026 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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