2011

U.S. Department of the Interior

U.S. Geological Survey

Phreatophytic Land-Cover Map of the Northern and 

Central Great Basin Ecoregion: California, Idaho, 

Nevada, Utah, Oregon, and Wyoming

By Amy M. Mathie, Toby L. Welborn, David D. Susong, and Mary L. Tumbusch

Pamphlet to accompany

Scientific Investigations Map 3169
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Viginia: 2011

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Suggested citation:

Mathie, A.M., Welborn, T.L., Susong, D.D., and Tumbusch, M.L., 2011, Phreatophytic land-cover map of the 

northern and central Great Basin Ecoregion: California, Idaho, Nevada, Utah, Oregon, and Wyoming: U.S. 

Geological Survey Scientific Investigations Map 3169, available at http://pubs.usgs.gov/sim/3169/.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Methods ..........................................................................................................................................................1

Results ............................................................................................................................................................3

Comparison with Other Mapped Groundwater Discharge Areas ...............................................5

Limitations and Recommendations for Use .....................................................................................5

Summary .........................................................................................................................................................7

References Cited ...........................................................................................................................................7

Additional References ..................................................................................................................................8

Appendix .........................................................................................................................................................9

Figures

1. Great Basin Integrated Management (GBILM) study area, California, Idaho, Nevada, and 

Utah. ...................................................................................................................................................2

Tables

1. Land-cover data sources. .......................................................................................................................3

2. Source and description of selected land-cover classes. .................................................................4

3. Representative statistics of total phreatophyte land-cover classes comprised in the 

Phreatophytic Land cover of the United States Great Basin Ecoregion map. ......................6

4. Comparison of phreatophyte land-cover classes from the Phreatophytic Land cover in 

the United States Great Basin Ecoregion map and BARCASS Potential Groundwater 

Discharge Areas. .............................................................................................................................7

Appendix .........................................................................................................................................................9

iii
Conversion Factors

Multiply By To obtain

Length

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Vertical coordinate information is referenced to the North American 

Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

vi
1

Abstract

Increasing water use and changing climate in the Great 

Basin of the western United States are likely affecting the distribution of phreatophytic vegetation in the region. Phreatophytic 

plant communities that depend on groundwater are susceptible to natural and anthropogenic changes to hydrologic flow 

systems. The purpose of this report is to document the methods 

used to create the accompanying map that delineates areas of 

the Great Basin that have the greatest potential to support phreatophytic vegetation. Several data sets were used to develop the 

data displayed on the map, including Shrub Map (a land-cover 

data set derived from the Regional Gap Analysis Program) 

and Gap Analysis Program (GAP) data sets for California and 

Wyoming. In addition, the analysis used the surface landforms 

from the U.S. Geological Survey (USGS) Global Ecosystems 

Mapping Project data to delineate regions of the study area 

based on topographic relief that are most favorable to support 

phreatophytic vegetation. Using spatial analysis techniques 

in a GIS, phreatophytic vegetation classes identified within 

Shrub Map and GAP were selected and compared to the spatial 

distribution of selected landforms in the study area to delineate 

areas of phreatophyte vegetation. Results were compared to 

more detailed studies conducted in selected areas. A general 

qualitative description of the data and the limitations of the base 

data determined that these results provide a regional overview 

but are not intended for localized studies or as a substitute for 

detailed field analysis. The map is intended as a decision-support aide for land managers to better understand, anticipate, and 

respond to ecosystem changes in the Great Basin.

Introduction

The withdrawals and interbasin transfers of groundwater within the arid Great Basin have increased as the human 

population and the demand for water have grown. As water has 

been developed and used, hydrologic flow systems in basins 

change and begin to re-equilibrate toward a new equilibrium. At 

the land surface, the vegetation distribution, which is dependent 

on groundwater and surface water, must adapt to the changing 

hydrologic regime (Naiman and Turner, 2000; Schultz, 2001; 

Elmore and others, 2003; Patten and others, 2007). The objective of this report is to delineate phreatophytic vegetation in 

the Great Basin using existing data sets and, thereby, provide 

a regional view of areas that may be potentially sensitive to 

groundwater extraction to aid land-management decisionmaking. For this report, phreatophytes are defined as plants that 

derive a substantial portion of their water needs from groundwater and that are dependent on groundwater for long-term 

survival. This definition includes wetland and riparian species, 

as well as more drought-stress-tolerant species that utilize 

groundwater from greater depths (White, 1932; Richards and 

Caldwell, 1987; Phillips, 1963). Water-level change, both rising 

and falling groundwater levels, can have consequences on 

phreatophytic communities (Namburg and others, 2005; Ridolfi 

and others, 2007). Phreatophytes are the principle mechanism of 

natural groundwater discharge within the Great Basin (Nichols, 1994) and are an important part of the groundwater budget 

for the region at nearly 40% (V.M. Heilweil, USGS, written 

commun., 2009). Long-term changes to the hydrology of the 

Great Basin, both anthropogenic and natural, will affect the 

distribution of phreatophytic communities and species behavior.

The study area for this investigation (fig. 1) is larger than 

the hydrographically defined Great Basin (Fenneman and 

Johnson, 1946) and is largely based on a combination of three 

Environmental Protection Agency (EPA) Level III ecoregions: 

Northern Basin and Range, Central Basin and Range, and Snake 

River Plain (Omernik, 1987). The study also includes areas 

that are part of the Bureau of Land Management (BLM) Great 

Basin Restoration Initiative (http://www.blm.gov/id/st/en/prog/

gbri.html) that are not within the three EPA ecoregions. Consequently, the study boundary expands the traditional hydrologic 

definition of the Great Basin as a region of internal drainage (Fenneman and Johnson, 1946) and includes parts of the 

Columbia Plateau, which shares physical similarities (climate 

and vegetation) with the Great Basin, as well as many of the 

same management issues (Miller and others, 2010). Thus, the 

study area encompasses over 111 million acres in 6 western 

states (California, Idaho, Nevada, Oregon, Utah, and Wyoming). Almost 80 percent of this area is public land, including 

about 80 percent managed by the BLM.

Methods

The focus of our research was to identify areas within 

the Great Basin that have the highest potential occurrence of 

phreatophyte vegetation based on spatial analysis of existing 

land-cover data sets. For the purposes of this report and the 

accompanying map, phreatophytes are defined as plant species 

that utilize shallow groundwater. Phreatophytes, by definition, 

withdraw shallow groundwater and have tap roots that extend 

to depths of 10 to nearly 50 ft below the land surface, depending on the species (White, 1932; Richards and Caldwell, 1987; 

Phillips, 1963). Vegetation along upland stream channels and 

vegetation that might use groundwater from upland perched 

groundwater systems were not included in the analysis. The 

general approach to delineate coverage of phreatophytic vegetation was to identify and combine land-cover vegetation classes 

that were predominantly phreatophytic species, then to compare 

the distribution of those classes and combine the results with 

targeted landforms data generated from elevation data (specifically, slope and relief). The distribution of phreatophytic 

vegetation was estimated through multistep geospatial analysis 

described in more detail below.

Shrub Map, a regional land-cover data set developed from 

SW ReGAP data and produced using a decision tree classifier, was utilized as the primary source for the vegetation land 

cover (http://sagemap.wr.usgs.gov/ShrubMap.aspx). Shrub 

Map is a 30-m2 resolution raster product of the U.S. Geological 

Survey SAGEMAP project and was created to assist research 

and management of sage grouse and shrubsteppe systems. For 

areas in the study area not covered by Shrub Map, 1990 GAP 
2

Figure 1. Great Basin Integrated Management study area, California, Idaho, Nevada, Oregon, and Utah.

Sacramento

Reno Fallon

Carson City

Las Vegas

Ely

Saint George

Delta

Elko

Boise

Bend

Ogden

Logan

Salt Lake City

Pocatello

NEVADA

OREGON IDAHO

UTAH

CALIFORNIA

ARIZONA

 ̈¦§80

 ̈¦§80

 ̈¦§70

 ̈¦§86

 ̈¦§15

¤£395

¤£395

¤£395

¤£395

¤£6

¤£6

¤£6

¤£50

¤£50

¤£20 ¤£20

¤£95

¤£0

123°W 122°W 121°W 120°W 119°W 118°W 117°W 116°W 115°W 114°W 113°W 112°W 111°W 110°W

45°N

44°N

43°N

42°N

41°N

40°N

39°N

38°N

37°N

36°N

35°N

0 50 100

0 10050 200 Kilometers

Great Basin study area from Omnerick, 1987. Shaded-relief base from GTOPO30 200 Miles

data sets from the U.S. Geological Survey EROS Data Center Distributed Active 

Archive Center (EDC DACC), 1996. Albers Equal-Area Conic projection, North 

American Dautm of 1983. Standard parallels 25°30’00’’ and 45°30’00’’, central 

meridian, 96°00’00’’ W, latitude of origin 23°00’00’’
3

data was used for California and Wyoming (http://gapanalysis.

nbii.gov/portal). GAP data was created for states and regions 

to provide regional assessments of natural land-cover vegetation for applications in land management decision-making. For 

our analysis, the 90-m2-resolution California and the 100-m2

resolution Wyoming GAP data sets were resampled to a finer 

30-m2 resolution to facilitate data processing. Although resampling of coarse resolution data to higher resolutions is not a 

typical practice, the process was deemed appropriate owing to 

the extensive coverage of the 30-m2 Shrub Map data within the 

study area.

Geomorphic features were identified from the USGS Global 

Ecosystems Mapping Project landforms data set (Cress and 

others, 2009; Sayre and others, 2009), which largely utilized 

a method developed by the Missouri Resource Assessment 

Partnership (MoRAP; http://morap.missouri.edu/). The MoRAP 

method to classify land surface forms uses only slope and local 

relief derived from neighborhood analysis on the cells of 30-m2

elevation data with a 1-km2 moving window and is a modification of earlier work by Hammond (1964a, 1964b), who developed classes from three topographic variables: slope, local relief, 

and profile type. The USGS landform data set contains ten geomorphic classes: flat plains (gently sloping and local relief ≤15 

m), smooth plains, irregular plains, escarpments, low hills, hills, 

breaks/foothills, low mountains, high mountains/deep canyons, 

and drainage channels (Cress and others, 2009). The landform 

data set was used in this study to estimate, at a regional scale, 

plant communities (capable of phreatophytic behavior) that are 

likely drawing on groundwater in the Great Basin. Thus, only the 

flat plains category was used in our analysis, because it limited 

distribution to areas of shallow groundwater.

Mapping the distribution of phreatophytes involved the 

following general procedures: (1) compiling, merging, and integrating spatial and tabular data layers into a GIS; (2) identifying 

phreatophytic plant species from literature sources; (3) selecting targeted phreatophyte vegetation classes from Shrub Map, 

California GAP, and Wyoming GAP data sets; (4) analyzing 

landforms and land-cover data sets using conditional analyses 

to map phreatophytic plant communities; and (5) comparing 

results with published local studies. The appendix includes a list 

of phreatophyte plant species and the literature sources. Using 

the class descriptions documented for Shrub Map and GAP data 

sets (table 1), land-cover classes that included phreatophytic 

plants were identified by comparing the dominant species 

recorded for each class against the list of phreatophytic species compiled from the literature. The subsequent results were 

further checked (1) by consultation with Dr. Eric Peterson, a 

vegetation ecologist from the Nevada Natural Heritage Program, and (2) by comparison with groundwater discharge areas 

identified by the USGS Basin and Range Carbonate Aquifer 

System Study (BARCASS) (Smith and others, 2007). A list of 

land-cover classes used from each source data set are provided 

in table 2.

The vegetation land-cover classes were analyzed with the 

flat plains landform using a conditional analysis. A conditional 

spatial analysis performs an if/else evaluation on each input 

cell of an input raster (http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Conditional_evaluation:_Con). 

The California and Wyoming GAP rasters were resampled to 

30-m2 pixel resolution to facilitate data processing with the 

30-m2 native resolution of the landforms data set. Additional 

land-cover data filtering was done within the Snake River Plain 

Ecoregion boundary (Omernik, 1987); specifically, the InterMountain Basins Big Sagebrush Shrubland was geospatially 

clipped because it was unlikely, given the groundwater and 

geomorphologic condition within this area, that the plant species identified as phreatophytes in other areas could function in 

the same manner. The results of these analyses, which removed 

terraces and upland regions from the land-cover categories, 

delineated the most probable areas for phreatophytes to grow in 

the lowest elevations of basins.

Hydrographic data shown on the final map product 

are derived from the USGS Streams and Water bodies of 

the United States data set (http://www.nationalatlas.gov/). 

Additional references used to confirm playa locations and 

geographic place names in the map are listed after the References Cited section of this report. The image resolution of the 

phreatophytic map data was set to conform to the 30-m2 Shrub 

Map land cover, because that data set covers the greatest extent 

of the study area. Although the California and Wyoming GAP 

data sets were resampled from coarser resolution to facilitate 

conditional analyses with the landforms data, the reliability of 

land cover in California and Wyoming retains the same data 

quality as their source GAP data (refer to the results section for 

further discussion).

Results

On the basis of our results, roughly 9 percent of the Great 

Basin study area is classified as phreatophytic vegetation land 

cover. Table 3 displays total area (in square meters and as percentage), mean patch size, patch number, and standard deviation 

of patch size identified by phreatophytic land-cover classes. A 

patch is a landscape unit defining a homogeneous area that differs from surrounding areas. Patches are physical and functional 

components affecting biomass, primary productivity, nutrient 

storage per unit area, and species composition and diversity 

(Forman and Gordon, 1986). Mean patch size is the mean size 

(square meters) of a land-cover class; patch number is the total 

number of patches, measuring the spatial character of a landcover class; and standard deviation of patch size measures the 

variation of a land-cover class (Leitão and others, 2006). Mean 

continuous patch size, patch number, and standard deviation of 

patch size characterize each land-cover class on the landscape in 

terms of proportion.

Table 1. Land-cover Data Documentation

• Shrub Map Land-cover Class descriptions: http://sagemap.wr.usgs.gov/FTP/

Documents/Shrubmap_Legend_Decriptions.pdf

• California GAP Land-cover Class descriptions and general documentation: 

http://www.biogeog.ucsb.edu/projects/gap/gap_home.html

• Wyoming GAP Land-cover Class descriptions and general documentation: 

http://www.sdvc.uwyo.edu/wbn/gap.html

 
4

Table 2. Source and description of selected land-cover classes.

Ecosystem class

 

Phreatophytic and potential

phreatophytic species

Selected land-cover classes chosen from Shrub Map

Inter-Mountain Basins Greasewood Wash Greasewood, patches of Saltgrass Meadow 

North American Warm Desert Wash Greasewood; Catclaw; Desertbroom (Baccharis); Desertwillow; Butternut/Nogal/

Walnut; Mesquite

Inter-Mountain Basins Big Sagebrush Shrubland Big Sagebush; Juniper; Greasewood; Saltbush

Sonora-Mojave Desert Mixed Salt Desert Shrub Saltbush; Pickleweed; Glasswort; Seepweed/Saltwort/Iodineweed/Inkweed; Sacaton; 

Saltgrass

Inter-Mountain Basins Greasewood Flat Greasewood; Saltbush; Sacaton; Saltgrass

North American Warm Desert Riparian Mesquite 

Bosque

Mesquite; Arrowweed; Willow

North American Arid West Emergent Marsh Tule; Desertrush/Wirerush/Wiregrass

Mediterranean Californian Alkali Marsh Saltgrass; Wirerush/Wiregrass; Tule; Saltbush

Temperate Pacific Freshwater Emergent Marsh Tule; Wiregrass/Wirerush

Riparian No species information available

Invasive Southwest Riparian Woodland Shrubland Salt Cedar (Tamarix)

Selected land-cover classes chosen from California GAP

Great Basin Mixed Scrub Great Basin Sagebrush, Antelope bush, Rabbitbrush, Saltbush

Big Sagebrush Scrub Great Basin Sagebrush, Low sagebrush

Rabbitbrush Scrub Rabbitbrush, Low sagebrush

Desert Greasewood Scrub Greasewood, Bud sagebrush, Great Basin Sagebrush

Alkali Meadow Saltgrass, Alkali sacaton, Saltbush

Great Basin Wet Meadow Great Basin wet meadow spp., Freshwater sedge

Modoc-Great Basin Cottonwood-Willow Riparian 

Forest

Willow, Fremont cottonwood, Box elder

Modoc-Great Basin Riparian Scrub Willow, Wet meadow Sedge, Rush, Water Birch, Great Basin Sagebrush

Selected land-cover classes chosen from Wyoming GAP

Wyoming Big Sagebrush Wyoming big sagebrush is the dominant shrub with total shrub cover comprising more 

than 25% of the total veg cover. This class type is variable: includes the full range from 

dense, homogenous Wyoming big sagebrush to sparsely vegetated arid areas where 

Wyoming big sage is the dominant shrub.

Greasewood Fans and Flats Greasewood comprises more than 75% of the total shrub cover within areas where 

shrubs comprise more than 25% of the total veg cover.

Forest-dominated Riparian Riparian zones where tree species dominate. Usually cottonwood species, but can also 

be aspen, box elder, or a variety of conifer species. (Trees must occupy more than 25% 

of the vegetation cover within the riparian zone.)

Shrub-dominated Riparian Riparian zones where shrubs dominate. Shrubs often include willow species, Artemisia species and /or greasewood but other shrubs (e.g. hawthorn, wild plum, birch, 

alder, tamarisk, shrubby cinquefoil) may be present or dominant. Area also includes 

alpine riparian zones dominated by Salix species or other shrubs. (Shrubs must comprise more than 25% of the vegetation cover within riparian zone)

 
5

Comparison with Other Mapped Groundwater 

Discharge Areas

Mapped phreatophytic vegetation communities were 

compared to existing Potential Groundwater Discharge Areas 

(fig. 2, map sheet) published for the Basin and Range Carbonate 

Aquifer System Study (BARCASS). The BARCASS Potential 

Groundwater Discharge Areas were derived using field techniques described in Smith and others (2007). The Potential 

Groundwater Discharge Areas were developed by combining 

and integrating phreatophyte boundaries delineated in previous studies, numerous mapping efforts, and phreatophyte 

extents mapped for the BARCASS study by an aerial survey 

done in 2005 (Smith and others, 2007). Because the focus of 

the BARCASS study was to delineate areas of groundwater 

discharge and to quantify evapotranspiration, the comparison of 

the two data sets is not straightforward. However, this comparison offers a quantitative assessment of the data derived for 

this study compared to an existing, published methodology. 

Table 4 shows the results of the comparison between the two 

data sets. The largest discrepancies in delineated acreage are 

in Snake Valley and Spring Valley, 279,571 acres and 95,186 

acres, respectively, where the Shrub Map and landforms method 

underestimated when compared to the BARCASS methods. 

The major differences in acreage between the two studies may 

be attributed to the different methodologies. The map accompanying this report utilized existing, documented Shrub Map, 

GAP, and MoRAP data while the BARCASS Potential Areas 

of Groundwater Discharge compiled and integrated existing 

documented data and observed field data. The exclusion of the 

playa land-cover classes and the inclusion of riparian land-cover 

classes and other vegetation land-cover classes that may be utilizing localized groundwater systems may also have influenced 

the comparison. This comparison emphasizes that the accompanying map is for regional analysis only.

Limitations and Recommendations for Use

Because of the large geographic area analyzed, multiple 

input data sets with varying source data scales, collection dates, 

and analytical techniques/methodologies were required for 

use in our analysis. Combining such data sets, however, can 

introduce error. The Great Basin Shrub Map, which provides 

coverage for the majority of our study area, is an enhancement 

of the Southwest ReGAP with a minimum mapping unit of one 

acre (table 1). The Wyoming GAP analysis for the Great Basin 

study area was completed using image interpretation on scenes 

that were not atmospherically corrected or edge-matched 

(Merrill and others, 1996). An informal accuracy assessment 

was done by field checking classifications during the summer 

of 1994. Field checks indicated that about 80 percent of the 

12 percent of the polygons reviewed were acceptable (Driese 

and others, 1997). However, it was noted that the minimum 

mapping unit of 1 hectare made ground verification difficult. A 

formal statistical evaluation was initiated to evaluate airborne 

videography as a tool to assess accuracy and to utilize the 

application of fuzzy accuracy assessment techniques (Reiners 

Of the 6,722,143 acres identified as phreatophytic land 

cover, Inter-Mountain Basins Greasewood Flat and Inter-Mountain Basins Big Sagebrush Shrubland vegetation classes account 

for the largest percentages at 52 percent and 34 percent, respectively. Shrub-dominated Riparian, Desert Greasewood Scrub, 

and Alkali Meadow have the largest mean continuous patch 

sizes at 1,234 acres, 976 acres, and 722 acres, respectively. 

Inter-Mountain Basins Big Sagebrush Shrubland had the largest number of individual patches (over 125,500) with a mean 

continuous patch size of 28 acres. This illustrates that, while the 

Shrub-Dominated Riparian is found in five patches, the areas 

are large, continuous areas; whereas, the Inter-Mountain Basins 

Greasewood Flat, the largest land-cover class by area, consists 

of many small, noncontinuous patches confined to valley floors. 

Caution must be used in assessing continuous mean patch size 

of classifications from the California and Wyoming GAP data, 

because the combining of these data sets with the more refined 

Shrub Map required the 100-m2 resolution to be resampled into 

several continuous 30-m2 cells—a process likely to produce 

erroneous pixel clustering in some locations.

The extent of the Flat Plains landform was used to limit 

the distribution of the land-cover classes to the lower part of 

the basin where groundwater levels typically are at or near 

land surface. In the northern Great Basin, along the Snake 

River Plain and Owyhee Uplands, the landscape differs from 

the majority of the Great Basin, because the area is dominated 

by flood basalts and does not have the typical basin and range 

structure. The conditional analysis that was conducted—where 

land-cover classes were isolated to the lowest portions of 

basins, or Flat Plains—assisted in limiting the occurrence of 

mapping anomalies from such classes as Inter-Mountain Basins 

Big Sagebrush Shrubland, which extends from the lowest parts 

of valleys into upland areas and significantly dominates vast 

amounts of acreage within the study area (table 3). Accordingly, the distribution of Inter-Mountain Greasewood became 

mottled but became more consistent when combined with 

observations made from field spot-checks after applying the 

Flat Plains landform restriction. Nonetheless, given the considerable percentage accounted for by these two classes, any 

mapping errors within the Inter-Mountain Basins Greasewood 

Flat and Inter-Mountain Basins Big Sagebrush Shrubland land 

cover could have a significant impact on the total estimate of 

phreatophytic vegetation.

As mentioned, phreatophytes withdraw shallow groundwater using tap roots that extend to depths as much as 50 ft 

below the land surface, depending on the species (White, 1932; 

Richards and Caldwell, 1987; Phillips, 1963). The ability of 

the plants to use water from these depths depends on a number 

of factors including plant type, annual precipitation, depth to 

the water table, soil properties including soil moisture, matrix 

potential, plant characteristics, and water quality (Nichols, 

1994; Namberg and others, 2005; Dawson, 1993). A comparison 

of measured groundwater levels, precipitation, soil properties, and distributions of phreatophytic vegetation classes were 

beyond the scope of this study but would greatly improve the 

functionality of this map. Consequently, we reiterate that the 

design of the methodology for this study was designed for landmanagement decision-making at a regional scale.
6

Table 3. Representative statistics of total phreatophyte land-cover classes from the Phreatophytic Land Cover of the 

United States Great Basin Ecoregion map.

Land-cover class

 

Total area

(acres)

Total area (%)

 

Mean patch size

(acres)

Patch

number 

Standard deviation of

patch size (acres)

Inter-Mountain Basins Greasewood Flat1 3,484,237 51.8 28 125,581 1,179

Inter-Mountain Basins Big Sagebrush 

Shrubland1

2,276,324 33.9 35 64,717 904

Riparian1 370,600 5.5 10 38,148 156

North American Arid West Emergent 

Marsh1

173,630 2.6 13 12,984 204

Great Basin Mixed Shrub2 113,416 1.7 289 393 1,574

Desert Greasewood Scrub2 104,418 1.6 976 107 7,471

Alkali Meadow2 84,444 1.3 722 117 4,215

Sonora-Mojave Desert Mixed Salt Desert 

Shrub1

34,138 0.5 22 1,571 237

Great Basin Wet Meadow2 26,904 0.4 292 92 722

Invasive Southwest Riparian Woodland 

Shrubland1

15,860 0.2 10 1,667 92

Temperate Pacific Freshwater Emergent 

Marsh1

8,619 0.1 19 447 272

Shrub-dominated Riparian3 6,168 0.1 1,234 5 2,682

Mediterranean CA Alkali Marsh1 5,809 0.1 22 270 139

Big Sagebrush Scrub2 4,851 0.1 323 15 690

Inter-Mountain Basins Greasewood 

Wash1

3,741 0.1 7 504 35

Rabbitbrush Scrub2 3,496 0.1 206 17 497

Wyoming Big Sagebrush3 3,046 0.0 66 46 222

Modoc-Great Basin Riparian Scrub2 1,726 0.0 58 30 181

Greasewood Fans and Flats3 267 0.0 19 14 46

North American Warm Desert Wash1 250 0.0 4 67 9

Modoc-Great Basin Cottonwood-Willow 

Riparian Forest2

125 0.0 16 8 31

Forest-dominated Riparian3 71 0.0 8 9 11

North American Warm Desert Riparian 

Mesquite Bosque1

4

 

0.0

 

1

 

4

 

1

 

1Shrub Map Land-Cover Class (http://sagemap.wr.usgs.gov/FTP/Documents/Shrubmap_Legend_Decriptions.pdf).

2California GAP Land-Cover Class (http://www.biogeog.ucsb.edu/projects/gap/gap_home.html).

3Wyoming GAP Land-Cover Class (http://www.sdvc.uwyo.edu/wbn/gap.html).
7

and others, 2000), but it was never completed. The California 

GAP analysis was completed using Landsat TM imagery from 

the summer of 1990, 1990 high-altitude color infrared photography, California Vegetation Type Maps based on field surveys 

conducted between 1928 and 1940, and miscellaneous vegetation maps and surveys conducted with a minimum mapping 

unit of 1 hectare near the time of the GAP analysis (Davis and 

others, 1998).

Estimates on area and classifications are sensitive to the 

accuracy and precision of the source data, as well as the map 

scale. Our analysis provides a regional overview of the distribution for potential areas of phreatophytic vegetation that could be 

affected by groundwater-level change. This study was designed 

to provide a regional context or a base content for finer-level 

analyses. These data are not designed to be used as a 1:24,000-

scale or finer data source, nor are they a substitute for a detailed 

field analysis.

Summary

Utilizing existing data sets, phreatophytic vegetation was 

mapped in the Great Basin. Shrub Map and GAP vegetation data 

were combined with landform classes derived from elevation 

data to delineate phreatophytes that are utilizing groundwater 

from basin- and regional-scale groundwater flow systems. Our 

study documents the methods used to delineate the communities and the limitations of the derived data set. Inter-Mountain 

Basins Greasewood Flats were the most common phreatophytic 

classification found throughout the Great Basin and account for 

52 percent of the mapped phreatophytes. The resulting geographic data set and map were derived from regional-scale data 

sets and contain limitations defined by the original base data.

References Cited

Carman, R.L., 1993, Measurement of evapotranspiration in 

phreatophyte areas, Smith Creek Valley and Carson Desert, 

west-central Nevada, 1983: U.S. Geological Survey WaterResources Investigations Report 89-4118, available at 

http://pubs.er.usgs.gov/usgspubs/wri/wri894118.

Cress, J.J., Sayre, Roger, Comer, Patrick, and Warner, Harumi, 

2009, Terrestrial ecosystems—Land surface forms of the 

conterminous United States: U.S. Geological Survey Scientific Investigations Map 3085, scale 1:5,000,000, 1 sheet, 

available at http://pubs.usgs.gov/sim/3085.

Czarnecki, J.B., and Stannard, D.I., 1997, Geohydrology and 

evapotranspiration at Franklin Lake playa, Inyo County, 

California, with a section on Estimating evapotranspiration 

using the energy-budget eddy-correlation technique: Water 

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Land Cover in the United States Great Basin Ecoregion map and the Basin and Range 

Carbonate Aquifer System Study (BARCASS) potential groundwater discharge areas.

Hydrographic area

 

 

Phreatophyte land-cover

classes (acres)

 

BARCASS

potential groundwater

discharge area (acres)

Percent

difference

 

White River Valley, NV 142,767 180,497 23

Steptoe Valley, NV 138,857 184,351 28

Butte Valley, NV 107,479 69,848 42

Lake Valley, NV 91,249 56,458 47

Spring Valley, NV 89,591 184,777 69

Snake Valley, NV 74,678 354,249 130

Long Valley, NV 64,309 18,371 111

Newark Valley, NV 56,380 86,713 42

Cave Valley, NV 33,158 13,499 84

Jakes Valley, NV 33,127 1,254 185

Little Smoky Valley, NV 

(northern part)

21,731 6,406 109

Little Smoky Valley, NV 

(southern part)

6,526 0 200

Tippett Valley, NV 781 7,819 164
8

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Additional References

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comp. ed.): New York, NY, Crown Publishers, plates 99 

and 107.

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(SSURGO) Database: U.S. Department of Agriculture, 

Natural Resources Conservation Service, accessed July 

2008, at http://soildatamart.nrcs.usda.gov.
9

List of common and potential phreatophytes in the northern and central Great Basin, western United States, that were identified from a detailed literature search (Carmen, 1993; Czarnecki and Stannard, 1997; Munz and Keck, 1968; Nichols, 2000; Robinson, 1958; Robinson and 

Waananen, 1970). 

Common Name Species Subspecies

Alder Alnus

Alfafa Medicago Sativa

Arrowweed Pluchea Sericea

Ash, Arizona and velvet Fraxinus Velutina

Aspen, quaking Populus Tremuloides

Aster, spiny Aster Spinosus

Athel, tree Tamarix Aphylla

Baccharis Baccharis Sarothroides; Emoryi; Sergiloides

Batamote Baccharis Glutinosa

Bermuda Grass; Wire Grass Cynodon Dactylon

Boxelder Scer Negundo

Buffaloberry Shepherdia

Burrobush Hymenoclea Monogyra; Salsola

Butternut Juglans Micorcarpa

Camelthorn Alhagi Camelorum

Carrizo Phragmites Communis

Catclaw Acacia Greggii

Chamiso Atriplex Canescens

Chamiza Atriplex Canescens

Cinquefoil Dasiphora Fruticosa

Cottonwood Populus Acuminata; Angustifolia; Balsamifera; Deltoides; Fremontii

Cottonwood Populus Sargentii; Texana; Trichocarpa; Weslizeni

Cumaru Celtis Reticulata

Desertbroom Baccharis Sarothroides

Desertrush Juncus Cooperi

Desertwillow Chilopsis Linearis

Devilsclaw Acacia Greggii

Elder; Elderberry Sambucus

Glasswort Salicornia Europaea

Goldenrod Aplopappus Heterophyllus

Greasewood Sarcobatus Vermiculatus

Hackberry Celtis Reticulata

Heliotrope Heliotropium Eruassavicum

Inkweed Suaeda Torreyana

Iodinebush Allenrolfea Accidentalis

Iodineweed Suaeda Torreyana

Juniper, Rocky Mountain Juniperus Scopulorum

Kom Celtis Reticulata

Lenscale Atriplex Lentiformis

Lovegrass, alkali Eragrostis Obtusiflora

Mesquite Prosopis Juliflora; Pubescens; Veluntina

Mulefat Baccharis Viminea

Nogal Juglans Microcarpa

Oak, California live Quercus Agrifolia

Appendix
10

List of common and potential phreatophytes in the northern and central Great Basin, western United States, that were identified from a detailed literature search (Carmen, 1993; Czarnecki and Stannard, 1997; Munz and Keck, 1968; Nichols, 2000; Robinson, 1958; Robinson and 

Waananen, 1970).—Continued 

Common Name Species Subspecies

Oak, Roble Quercus Lobata

Palm, California and fan Washingtonia Filifera

Palo Verde, blue Cercidium Floridum

Pickleweed Allenrolfea Occidentalis

Purslane, lowland Sesuvium Portulocostrum

Pusley, Chinese Heliotropium Curvassavicum

Quailbrush Atriplex Lentiformis

Rabbitbrush Chrysothamnus Nauseosus; Pumilus

Reed; Reedgrass Phragmites Communis

Rosinbrush Baccharis Sarothroides

Sacaton Sporobolus Wrightii; Airoides

Sagebush Artemisia Tridentata

Saltbush Atriplex Canescens; Lentiformis

Saltbush Atriplex Parryi

Saltcedar, Tamarisk Tamarix Gallica; Aphylla; Pentandra

Saltgrass Distichlis Spicata; Stricta

Saltgrass, Mexican Eragrostis Obtusiflora

Saltwort Suaeda Depressa

Sea-purslane Sesuvium Verrucosum

Sedge Carex

Seepweed Suaeda Depressa; Suffrutescens; Torreyana

Seepweed Suaeda Fruticosa

Seepwillow Baccharis Glutinosa

Sequoia Sequoia Gigantea

Sesuvium Sesuvium Verrucosum

Smoketree; Smokethorn Dalea Spinosa

Sprangletop Leptochloa Fascicularis

Spruce, Englemann Picea Englemanni

Swampcedar Juniperus Scopulorum

Sycamore, Arizona Platanus Wrightii

Tornillo Prosopis Pubescens

Tule Scirpus

Una de gato Acacia Greggii

Vanadium bush Cowania Stansburiana

Vetch, sweet Hedysarum Boreale

Walnut Juglans Microcarpa

Watermotie; Waterwillow Baccharis Glutinosa

Waterweed Baccharis Sergiloides

Wildrose Rosa

Wildrye Elymus Triticoides; Condensatus

Willow Salix

Wiregrass; Wirerush Juncus Balticus

Yerba mansa Anemopsis Californica