USGS Professional Paper 1703—Ground-Water Recharge

in the Arid and Semiarid Southwestern United States—

Chapter G

Ground-Water Recharge From Small Intermittent Streams 

in the Western Mojave Desert, California

By John A. Izbicki, Russell U. Johnson, Justin Kulongoski, and Steven Predmore

Abstract 

Population growth has impacted ground-water resources 

in the western Mojave Desert, where declining water 

levels suggest that recharge rates have not kept pace with 

withdrawals. Recharge from the Mojave River, the largest 

hydrographic feature in the study area, is relatively well 

characterized. In contrast, recharge from numerous smaller 

streams that convey runoff from the bounding mountains 

is poorly characterized. The current study examined four 

representative streams to assess recharge from these intermittent sources. Hydraulic, thermal, geomorphic, chemical, and 

isotopic data were used to study recharge processes, from 

streamflow generation and infiltration to percolation through 

the unsaturated zone. Ground-water movement away from 

recharge areas was also assessed.

Infiltration in amounts sufficient to have a measurable effect on subsurface temperature profiles did not occur 

in every year in instrumented study reaches. In addition to 

streamflow availability, results showed the importance of sediment texture in controlling infiltration and eventual recharge. 

Infiltration amounts of about 0.7 meters per year were an 

approximate threshold for the occurrence of ground-water 

recharge. Estimated travel times through the thick unsaturated 

zones underlying channels reached several hundred years. 

Recharging fluxes were influenced by stratigraphic complexity and depositional dynamics. Because of channel meandering, not all water that penetrates beneath the root zone can be 

assumed to become recharge on active alluvial fans.

Away from study washes, elevated chloride concentrations and highly negative water potentials beneath the root 

zone indicated negligible recharge from direct infiltration of 

precipitation under current climatic conditions. In upstream 

portions of washes, generally low subsurface chloride concentrations and near-zero water potentials indicated downward 

movement of water toward the water table, driven primarily 

by gravity. Recharging conditions did not extend to the distal 

ends of all washes. Where urbanization had concentrated spatially distributed runoff into a small number of fixed channels, 

enhanced infiltration induced recharging conditions, mobilizing accumulated chloride.

Estimated amounts of ground-water recharge from the 

studied reaches were small. Extrapolating on the basis of 

drainage areas, the estimated aggregate recharge from small 

intermittent streams is minor compared to recharge from the 

Mojave River. Recharge is largely controlled by streamflow 

availability, which primarily reflects precipitation patterns. 

Precipitation in the Mojave Desert is strongly controlled by 

topography. Cool moist air masses from the Pacific Ocean are 

mostly blocked from entering the desert by the high mountains bordering its southern edge. Storms do, however, readily 

enter the region through Cajon Pass. These storms generate 

flow in the Mojave River that often reaches Afton Canyon, 

more than 150 kilometers downstream. The isotopic composition of ground water reflects the localization of recharge 

beneath the Mojave River. Similar processes occur near San 

Gorgonio Pass, 75 kilometers southeast from Cajon Pass 

along the bounding San Andreas Fault.

Introduction

The western Mojave Desert east of Los Angeles (fig. 1) 

is arid with hot, dry summers and cold winters. The population of the area, including the Palmdale/Lancaster areas to 

the west, the Victorville area, and the Yucca Valley area to 

the east, has increased rapidly from about 500,000 in 1990 to 

almost 670,000 in 2000 (California Department of Finance, 

2002a,b). Water supply is derived almost entirely from ground 

water, and pumping has increased with population. As a result 

of pumping in excess of recharge, water levels throughout 

the area have declined in recent years (Smith, 2003; Stamos 

and others, 2001; Mendez and Christensen, 1997; Stamos 

and Predmore, 1995). Declining water levels and increased 

competition for ground-water supplies has resulted in a series 

of lawsuits and adjudications of parts of the area along the 

Mojave River (California Supreme Court, 2000) and in Yucca 

Valley (California Superior Court, 1977).

A better understanding of the physical processes that control the spatial and temporal distribution of natural recharge 

may help resolve questions about ground-water availability 

and enable agencies responsible for water supply to better 

manage ground-water resources. Ground-water recharge from 

larger streams such as the Mojave River has great economic 

value and has been extensively studied by traditional methods 
158 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

15 

15 

215 

10 

40 

395 

18 

14 

58 

247 

247 

138 

62 

18 

Mojave River

Antelope 

Valley 

Afton 

Canyon 

Granite 

Mountain 

C

A

L I F O R N I A 

MAP 

AREA 

Los Angeles 

35o 

00' 

34o 

30' 

34o 

00' 

116o

 30' 116o 117 00' o 117 00' o 118 30' o 00' 

0 20 KILOMETERS 

0 20 MILES 

EXPLANATION

Streambed temperature sites USGS stream gages

Weather Station—Name shown

 if discussed in text

Instrumented borehole

 and designator

UOGW 

62 

0 

0 3 

3 MILES 

KILOMETERS 

116o 116 10' o 20' 

34o

10' 

34o

05' 

Quail 

Wash 

Yucca Wash

UQSW 

QSWC

LQSW 

Joshua

Tree

Sheep Creek 

Wash 

Big Rock 

Creek 

Wash 

15 

18 

138 

LSCW

UOGW

Oro Grande 

Wash 

117o 117 20' o

 50' 

34o 

15' 

34o 

35' 

VVWD LOGW 1–3

OGF

Mojave River

Victorvillle

0 10 20 KILOMETERS 

0 10 20 MILES 

395 

San Bernardino 

Mountains 

Cajon Pass 

San Gabriel Mountains 

Mormon 

Rock 

Palmdale

Lancaster

Victorville

MORONGO

GROUND-WATER

BASIN

MOJAVE RIVER

GROUND-WATER

BASIN

Twentynine 

Palms

Yucca 

Valley 

Barstow 

Figure 1. Location of study area in the western Mojave Desert, southern California.
Hydrogeologic Setting 159

(Thompson, 1929; California Department of Public Works, 

1934; California Department of Water Resources, 1967; Hardt, 

1971; Lines, 1996; Stamos and others, 2001). Recharge from 

small intermittent streams has not been as extensively studied 

but, in some areas, the aggregate recharge from these many 

small sources may represent a large part of the overall water 

budget in a basin. In addition, locations where even small 

amounts of natural recharge occur under present-day conditions may have value as potential sites for artificial recharge.

Purpose and Scope

The purpose of this paper is to describe the processes 

involved in focused recharge through thick unsaturated zones 

that underlie small intermittent streams in the western Mojave 

Desert. Understanding processes controlling recharge from 

small intermittent streams is important for assessing the 

regional water budget, and to determine if the aggregated 

recharge from the many small sources is greater or less than 

recharge from major sources such as the Mojave River.

Approach

This paper summarizes previously published results and 

ongoing work from a series of detailed U.S. Geological Survey 

studies addressing different aspects of natural recharge from 

intermittent streams in the western part of the Mojave Desert. 

In arid areas, natural recharge from these sources is typically 

small and difficult to study because it occurs intermittently at 

a wide range of temporal and spatial scales. A combination 

of physical, hydraulic, and chemical techniques were used to 

investigate different aspects of the recharge process—each 

technique constraining some aspect of the process. The use of 

multiple techniques was intended to describe the entire process, 

from frequency of streamflow and subsequent infiltration to the 

movement of water through the underlying unsaturated zone.

For the purpose of this study, the recharge process was 

divided into small increments on the basis of our understanding of natural recharge and our ability to measure and quantify 

each incremental step. Streamflow availability was determined 

from analysis of streambed temperature data. Infiltration of 

streamflow was determined from matric potential and borehole 

temperature data collected in the unsaturated zone beneath the 

stream channels. Stream reaches where deep infiltration (infiltration to depths below the root zone that presumably becomes 

ground-water recharge) occurred were determined from chloride 

profiles. Movement of water through the unsaturated zone to the 

underlying water table, in many cases several hundred meters 

below land surface, was evaluated of the basis of tritium data, 

numerical models, and a large-scale infiltration experiment.

Results from detailed studies along selected stream 

reaches were regionalized to the entire study area by using 

geomorphic techniques and isotopic data. The geomorphic 

techniques compared the stream drainage area to other stream 

drainage areas in the study area. The isotopic composition of 

ground water has preserved a record of the source, movement, 

and age of the water; interpretation of this record provides 

information on recharge from different sources within the 

basin through recent geologic time. As part of the interpretation of the isotopic record, large regional-scale sources of 

ground-water recharge were related to large-scale geologic 

features that focus precipitation, runoff, and subsequent 

ground-water recharge in a manner different from much of the 

arid southwestern United States.

Hydrogeologic Setting

The study area is the western Mojave Desert east of Los 

Angeles including the Mojave River Ground-Water Basin, 

the Morongo Ground-Water Basin and part of the Antelope 

Valley area along the northern slope of the San Bernardino 

and San Gabriel Mountains (fig. 1). The ground-water basins 

are defined on the basis of the contact between that alluvial 

valleys and the mountain front. The San Bernardino and Little 

San Bernardino Mountains to the east are composed largely 

of granitic rock. The San Gabriel Mountains are composed of 

granitic and metamorphic rock. For management purposes, 

these basins have been divided into smaller basins by the California Department of Water Resources (2003) on the basis of 

the areal extent of alluvial deposits, subsurface features such 

as faults and selected ground-water-flow divides.

The area is arid with hot, dry summers and cold winters 

(fig. 2). With the exception of the higher altitudes in the San 

Gabriel and San Bernardino Mountains, precipitation is generally about 150 mm/yr or less, but amounts may vary greatly 

from year to year. In most of the area, precipitation is greater 

during the winter rainy season (November-March) and occurs 

as a result of cyclonic storms moving inland from the Pacific 

Ocean. Although summer thunderstorms occur, especially in the 

southern part of the study area near Twentynine Palms, summer 

monsoonal precipitation that occurs throughout much of the 

southwestern United States is of lesser importance in this area.

With the exception of small streams—such as Big Rock 

Creek—that drain the higher altitudes of the San Gabriel and 

San Bernardino Mountains, and short reaches of the Mojave 

River —where ground water discharges at land surface—there 

are no perennial streams in the area. The Mojave River, the 

largest in the study area, drains about 5,500 km2

, about 

540 km2 of which are in the San Bernardino Mountains near 

Cajon Pass. Cajon Pass is a low altitude gap between the San 

Gabriel and San Bernardino Mountains. Moist air from the 

Pacific Ocean can enter the Mojave Desert through the pass 

without passing over the higher altitudes of the San Gabriel 

and San Bernardino Mountains and thus deliver precipitation 

to an otherwise rain-shadowed area. In some years winter 

precipitation near the pass gives rise to storm flow along the 

entire length of the Mojave River—reaching Afton Canyon, 

more than 156 km from the mountain front. A similar gap 

in the San Bernardino and San Jacinto Mountains forms San 
160 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

JAN MAR MAY JUL SEP NOV 

JAN MAR MAY JUL SEP NOV 

0 

5 

10 

15 

20 

25 

30 

35 

40 

MONTH 

TEMPERATURE, IN DEGREES CELSIUS 

0 

5 

10 

15 

20 

25 

30 

35 

40 

TEMPERATURE, IN DEGREES CELSIUS 

0 

10 

20 

30 

40 

50 

60 

70 

80 

PRECIPITATION, IN MILLIMETERS 

0 

10 

20 

30 

40 

50 

60 

70 

80 

PRECIPITATION, IN MILLIMETERS 

Victorville, CA 

Twentynine Palms, CA 

Average annual

temperature 20.1°C 

Average annual 

precipitation 116 mm 

Average annual

temperature 16.5°C 

Average annual 

precipitation 157 mm 

Figure 2. Monthly average temperature and precipitation for 

Victorville and Twentynine Palms, Calif. 1971–2000. Data from 

Western Regional Climate Center, http://www.wrcc.dri.edu, last 

accessed April 30, 2003.

Gorgonio Pass to the south of the study area and gives rise to 

winter precipitation in that area, although the effect is smaller 

than near Cajon Pass (Izbicki, 2004).

In the Mojave River Ground-Water Basin, two aquifers 

are pumped for water supply—the floodplain aquifer along 

the Mojave River and the surrounding and underlying regional 

aquifer. The floodplain aquifer consists of highly permeable 

sand and gravel deposited by the Mojave River. In most areas 

the deposits are less than 80-m thick and less than 

2.5 km wide; however the deposits are thicker and more areally extensive in the Mojave Valley area downstream from 

Barstow (Stamos and others, 2001). Average annual recharge 

to the floodplain aquifer from infiltration of surface flow in the 

Mojave River is about 47.6 hm3 (Stamos and others, 2001), but 

varies greatly from year to year in response to precipitation. 

The regional aquifer includes interconnected alluvial basins 

that drain toward the floodplain aquifer along the Mojave 

River and topographically closed basins that drain toward dry 

lakes. The deposits that compose the regional aquifer are less 

permeable than those of the floodplain aquifer, but may be 

more than 1,000-m thick in some areas. Annual recharge to the 

regional aquifer from the mountain block and from infiltration 

from small streams along the front of the San Gabriel and San 

Bernardino Mountains is about 13.2 hm3 (Stamos and others, 2001). Although average annual recharge to the regional 

aquifer is smaller than recharge along the Mojave River, these 

deposits contain large amounts of ground water in storage. 

The Morongo Ground-Water Basin contains a number 

of small, alluvial subbasins; each having separate groundwater flow systems typically terminating in dry lakes scattered 

throughout the area. These smaller alluvial basins are separated by faults and bedrock outcrops. Although the hydraulic 

properties of these subbasins vary spatially and with depth, 

they are more similar to those of the regional aquifer in the 

Mojave River Basin than to those of the floodplain aquifer 

along the Mojave River. In some areas, the alluvial subbasins 

may be more than 1,000 m thick and contain large amounts of 

ground water in storage. Aggregate recharge to the Morongo 

Ground-Water Basin due to infiltration from small streams 

at the front of the San Bernardino and Little San Bernardino 

Mountains has not been estimated.

The mechanisms by which surface flow from intermittent streams along the front of the San Gabriel and San 

Bernardino Mountains recharges underlying alluvial aquifers were studied along four washes—Oro Grande Wash 

and Sheep Creek Wash in the Mojave River Ground-Water 

Basin, Big Rock Creek Wash in Antelope Valley to the west 

of the Mojave River Ground-Water Basin, and Quail Wash 

in the southern part of the Morongo Ground-Water Basin. 

The total length of the selected washes is about 80 km. Each 

wash represents a range of climatic, geologic, and hydrologic 

conditions that control streamflow availability, infiltration 

of streamflow, movement of infiltrated water below the root 

zone (deep infiltration), and movement of water through the 

thick unsaturated zone to the water table, which varies up to 

several hundred meters below land surface.

Oro Grande Wash

Oro Grande Wash drains 6.2 km2 at the downstream study 

site along the 22.7-km study reach. Oro Grande Wash is the 

smallest drainage included in this study and is representative 

of similar washes near Cajon Pass (fig. 3). Due to tectonic 

activity along the San Andreas Fault and subsequent erosion 

near the pass, Oro Grande Wash is no longer connected to the 

mountains, and flow in the wash is derived entirely as runoff 

from precipitation that falls on the alluvial fan surface. In 

some years precipitation on the alluvial fan near Cajon Pass 

can exceed 800 mm/yr (Izbicki and others, 2000a), but the 

average is less than 400 mm/yr. Precipitation decreases away 

from the pass and in most years is less than 150 mm/yr along 

the downstream parts of the study reach.

On the basis of channel-geometry data (Lines, 1996), 

average annual flow in Oro Grande Wash near LOGW is 

estimated to be about 0.5 hm3

 (table 1). Streamflow that occurs 

is brief in duration, typically lasting less than an hour. The 

channel of the wash is about 3-m wide and is incised about 10 

to 20 m into the regional surface of the alluvial fan (fig. 4). As 
Hydrogeologic Setting 161

E 

D 

C 

B 

A 

Oro Grande Wash near LOQW-1 (December 2002). Channel 

sandy; width about 3 m. Infiltration rate about 0.28 m/hr.

Big Rock Creek gaging station, San Gabriel Mountains near 

Valyermo (10263500; March 2004). Channel is bedrock; width 

about 3 m. High flow is from snowmelt.

Sheep Creek Wash near USCW, about 2 km 

downstream from mountain front (March 2004). 

Channel cobbly; width about 80 m (flows rarely span 

channel). Infiltration rate about 0.14 m/hr.

Sheep Creek Wash near LSCW, about 13 km 

downstream from mountain front (March 2004). 

Channel silty; width about 3 m. Infiltration rate about 

0.04 m/hr.

Quail Wash near LQSW (March 2004). Channel sandy; 

width about 20 m. Infiltration rate about 0.79 m/hr. Flow 

in August 2004 eroded more than five meters of left 

bank.

Figure 3. Photographs of selected intermittent streams in the western Mojave Desert study area, southern California. 

A, Oro Grande Wash; B, upstream reach of Sheep Creek Wash; C, downstream reach of Sheep Creek Wash; D, perennial 

reach of Big Rock Creek; E, downstream reach of Quail Wash. Locations are shown on figure 1. Infiltration rates are in 

meters per hour (m/hr).
162 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

a result, flow in the wash has followed nearly the same course, 

repeatedly wetting the underlying unsaturated zone, since 

incision of the wash after development of Cajon Pass, about 

500,000 years ago (Meisling and Weldon, 1989). This repeated 

wetting has prevented development of the thick, impermeable caliche layers that underlie the alluvial fan away from 

the wash (Izbicki and others, 2000b, 2002). The bed of the 

wash is composed of sand along its entire length. Infiltration 

rates measured as part of this study by using a 1.2-m-diameter 

double-ring infiltrometer ranged from 1.3×10-2 to 2.2×10-2

cm/s (0.46–0.79 m/hr; table 2). Infiltration rates were lower 

near Cajon Pass and higher farther downstream.

The unsaturated zone underlying Oro Grande Wash 

ranges from more than 300-m thick near Cajon Pass to about 

130 m along the downstream parts of the study reach. The 

alluvial deposits are composed of younger deposits of sand 

and gravel, reworked from the surrounding Victorville fan, that 

partly backfills the incision of the wash to a depth of about 

7 m. These deposits are surrounded and underlain by older 

deposits of the Victorville fan (Meisling and Weldon, 1989) 

that consist of alternating layers of fluvially sorted sand, silt, 

and clay, with smaller amounts of gravel (Izbicki and others 2000a,b; Izbicki, 2002). The younger deposits are highly 

permeable, with saturated hydraulic conductivities of about 

5.5×10-3 cm/s (Izbicki, 2002). The Victorville fan deposits 

are less permeable, and the saturated hydraulic conductivity 

of core material collected from the unsaturated zone along 

downstream reaches of Oro Grande Wash near instrumented 

borehole VVWD ranged from about 7×10-4 to 4×10-6 cm/s 

(fig. 5). Areally extensive clay layers having an average 

thickness of 1.2 m, but often less than 0.3 m thick, are present 

within the deeper, older deposits. These lower permeability layers are believed to be buried soil horizons (paleosols; 

Izbicki, 2002; fig. 6). They have lower permeability that 

impedes the downward movement of water and increases 

the lateral movement of water away from the wash (Izbicki, 

2002; Nimmo and others, 2002). The statistical distribution of 

the low-permeability materials in the unsaturated zone along 

the downstream reaches of Oro Grande Wash was described 

by Izbicki (2002), and the effect of particle-size and sorting 

within the older deposits on unsaturated hydraulic properties 

was described by Winfield (2000).

Sheep Creek Wash

Sheep Creek Wash drains 36.8 km2 in the San Gabriel 

Mountains west of Cajon Pass (fig. 3). The conical shape 

of the alluvial fan underlying the wash directs runoff away 

from the active channel of the wash (fig. 4), and the drainage 

area along the 18.8-km study reach from the mountain front 

to the downstream measurement site is only 2.4 km2

. Sheep 

Creek flows intermittently as a result of runoff from the higher 

altitudes in the mountains. Precipitation at the higher altitudes 

of the San Gabriel Mountains averages more then 1,000 mm/

yr, with much of the precipitation falling as snow during the 

winter months. Precipitation decreases away from the mountain front and in most years is less than 150 mm/y along the 

downstream parts of the study reach.

On the basis of a relation between channel geometry and 

streamflow data (Lines, 1996), average annual flow in Sheep 

Creek Wash near the mountain front is estimated to be about 

3.1 hm3

 (table 1). In some years, sustained flows, lasting as 

long as several weeks, may occur near the mountain front 

as a result of snowmelt after wet winters. The bank-to-bank 

width of the wash ranges from about 80 m near the mountain 

front to about 3 m as flows decrease downstream. Most flows 

near the mountain front do not fill the entire channel, and thus 

the active channel is much narrower. Under predevelopment 

conditions, streamflow in Sheep Creek Wash did not necessarily follow the same course each year; and occasionally flowed 

in different channels in response to deposition and subsequent 

changes in the slope of the fan (fig. 4). As a result, flow in 

Sheep Creek Wash did not repeatedly wet the same material 

year after year in the same manner as did flow in Oro Grande 

Wash (Izbicki and others, 2002). In recent years, a series of 

levees has restricted streamflow to fewer active channels. Near 

the mountain front the bed of the wash is composed of boulders and cobbles in a matrix of silt and sand. Farther downstream the bed of the wash is composed of fine silt. Infiltration 

rates measured as part of this study by using a 1.2-m-diameter 

double-ring infiltrometer ranged from 0.1×10-2 to 0.4×10-2

cm/s (0.04–0.14 m/hr; table 2). Infiltration rates were higher 

near the mountain front and lower farther downstream.

The thickness of the unsaturated zone underlying the 

wash ranges from more than 300 m near the mountain front 

to about 150 m along the downstream parts of the study reach 

(Izbicki and others, 2002). Much of the alluvial material 

comprising the Sheep Creek fan was deposited by debris flows 

and is poorly sorted. Near the mountain front, the deposits are 

composed of cobbles and gravel in a matrix of coarse sand. 

Although some cobbles and gravels are present in the deposits 

farther from the mountain front, the deposits there are finer 

grained and the matrix is composed of silt. Deposition on the 

Sheep Creek fan must have been fairly rapid and continuous, 

as evidence of paleosols within the deposits was not observed 

in test-drilling logs collected by Izbicki and others (1995, 

2000a). Although the saturated hydraulic conductivity of the 

unsaturated deposits was not measured as part of this study, 

Winfield (2000) measured the physical properties, sorting, and 

water-retention characteristics. Winfield (2000) determined 

that differences in the water-retention characteristics between 

debris-flow deposits underlying Sheep Creek Wash and 

fluvially sorted deposits underlying Oro Grande Wash were 

determined primarily by the particle-size distribution of the 

material and not by a lack of fluvial sorting prior to deposition.

Big Rock Creek

Big Rock Creek drains 108 km2 in the San Gabriel 

Mountains to the west of the Mojave River Basin in Antelope 
Hydrogeologic Setting 163

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Figure 4. Geomorphic and hydrologic features of selected intermittent streams, western Mojave Desert study 

area, southern California. Arrows represent recharging water.
164 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

Table 1. Physical characteristics along study reaches of Oro Grande Wash, Sheep Creek, Big Rock Creek, and Quail Wash, 

western Mojave Desert, southern California.

[Drainage areas and altitudes are measured above the mountain front. Average annual flow at the mountain front was estimated from a relation 

between channel geometry and annual flow developed by Lines (1996), except for Big Rock Creek, for which flow was estimated from streamflow 

data at Valyermo, Calif., five kilometers upstream of the mountain front. Abbreviations: —, not applicable (Oro Grande Wash no longer connects 

to an upstream watershed); km, kilometers; km2, square kilometers; hm3, cubic hectometers]

Drainage 

area at 

mountain 

front,

in km2

Altitude1,

in meters Average 

annual 

flow,

in hm3

Length 

of study 

reach,

in km

Channel width,

in meters

Average 

slope of 

study reach,

in 

percent

Stream Maximum Average

At 

mountain 

front

At downstream 

site

Oro Grande Wash — — — 0.5 22.7 3. 3. 3.1

Sheep Creek Wash 36.8 2,594 1,948 3.1 18.8 80. 3. 4.9

Big Rock Creek 108. 2,829 1,769 16. 27.3 10. 40. 1.5

Quail Wash 237. 1,768 1,351 28. 15.2 10. 20. 1.7

1

National Geodetic Vertical Datum of 1929.

Table 2. Streambed characteristics and infiltration along study reaches of Oro Grande Wash, Sheep Creek Wash, and 

Quail Wash, western Mojave Desert, southern California.

[Instantaneous infiltration measured using a 1.2-meter-diameter double-ring infiltrometer. Annual infiltration rate and infiltration along study reach 

estimated from temperature data (Kulongoski and Izbicki, 2008). Abbreviations: —, negligible (based on chloride accumulation; see text); m/hr, 

meters per hour; m/yr, meters per year; m3, hm3, cubic hectometers]

Stream Description of stream 

channel

Instantaneous 

infiltration 

rate,

in m/hr

Annual 

infiltration 

rate,

in m/yr

Annual 

infiltration 

along study 

reach,

in hm3

Annual deep 

infiltration 

along study 

reach,

in hm3

Oro Grande Wash Medium sand 0.28–0.72 0.7–2.0 0.1 0.04

Sheep Creek Wash Cobbles near mountain 

front to silt downstream 0.04–0.14 0.7–1.3 0.58 0.51

Quail Wash Coarse sand 0.46–0.79 1

0.25 0.1 —

1

Infiltration rate and annual infiltration calculated for 20-kilometer reach of Yucca Wash (Yucca Valley to Coyote [dry] Lake), which includes the 

confluence with Quail Wash.

Valley (fig. 3). The drainage area along the 27.3-km study 

reach from the mountain front to the downstream measurement site is 13.3 km2

. Precipitation amounts in the area are 

similar to those in the adjacent Sheep Creek area. Big Rock 

Creek flows perennially near the mountain front, and on the 

basis of streamflow gaging data, the average annual flow is 

16.1 hm3

/yr. Flows are smaller and of shorter duration farther 

downstream. Streambed-temperature data and estimates of 

streamflow availability and frequency of flow from Big Rock 

Creek were included in this study for comparison with data 

from other streams having intermittent flow. Streambed-infiltration rates and the hydraulic properties of the underlying 

unsaturated zone were not characterized as part of this study.

Quail Wash

Quail Wash drains 237 km2 in the Little San Bernardino 

Mountains in the Morongo Basin (fig. 3). Precipitation in 

the higher altitudes of the Little San Bernardino Mountains 

is as much as 350 mm/yr. Precipitation at the lower altitudes 

typically averages less than 100 mm/yr. Although it has the 

largest drainage area, Quail Wash is the driest of the study 

washes. Unlike the other study washes, more precipitation 

falls in the Quail Wash drainage during the summer months 

than during the winter months. The drainage area at the 

downstream site, LQSW, includes runoff from 185 km2

 in 

the San Bernardino and Little San Bernardino Mountains 
Recharge Processes 165



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Figure 5. Distribution of saturated hydraulic conductivity values 

measured on core material collected from the unsaturated zone 

underlying the downstream reach of Oro Grande Wash (one site; 

total depth about 130 m) and Quail Wash (four sites; total depths 

about 15 m), western Mojave Desert, southern California. Figure 1 

shows site locations.

Figure 6. Heterogeneous alluvial deposits encountered 

during test drilling in the unsaturated zone underlying 

Oro Grande Wash near borehole VVWD, western Mojave 

Desert, California. Each pile represents the cuttings from 

a 0.3-m interval. Figure 1 shows the site location.

#LAY
RICHPALEOSOL

and alluvial valleys drained by Yucca Wash. Precipitation 

is greater in the area drained by Yucca Wash than in the 

area drained by Quail Wash, and more precipitation falls in 

this area during the winter months than during the summer 

months. Runoff from Yucca Wash has increased in recent 

years because of urbanization near Yucca Valley.

On the basis of a relation between channel geometry 

and streamflow data (Lines, 1996), average annual flow 

in Quail Wash was estimated to be about 28 hm3

 (table 1). 

Streamflow is more frequent and larger in magnitude along 

the downstream reach where flows from urban areas in 

Yucca Valley enter the wash. The channel of Quail Wash is 

about 10 m wide near the mountain front and about 20 m 

wide along downstream reaches where flows from urban 

areas are present. Streamflow along the downstream reach 

occurs more frequently during the winter rainy season than 

during the summer. Near the mountain front the position of 

the stream channel is constrained by alluvial fan deposits 

weathered from nearby hills. Farther from the mountain 

front the slope of the stream is small, about 0.3 percent, 

and the stream channel may change course as streamflow 

erodes the channel banks (fig. 4). The bed of the wash is 

composed of sand along its entire length. Infiltration rates 

measured as part of this study by using a 1.2 m diameter 

double-ring infiltrometer ranged from 1.3 × 10-2 to 2.2 × 10-2

cm/s (0.46–0.79 m/hr; table 2). Infiltration rates measured 

with the infiltrometer along Quail Wash decreased with distance from the mountain front to where it joins with Yucca 

Wash. Farther downstream, infiltration rates increased along 

stream reaches where the magnitude and frequency flow was 

increased by urbanization upstream.

The thickness of the unsaturated zone underlying the 

wash is about 150 m. The upper 15 m of these deposits were 

characterized by drilling as part of this study and are composed of fluvially sorted sand, with some gravel and silt. 

The sand was relatively homogeneous and lacked obvious 

paleosols. The saturated hydraulic conductivity of most core 

material collected from the unsaturated zone ranged from 

about 2 × 10-3 to 9 × 10-5 cm/s. The small range in hydraulic 

properties, in comparison with alluvial material underlying Oro Grande Wash, reflects the relatively homogeneous 

nature of the deposits, and the relatively continuous deposition with subsequent lack of soil development. Hydraulicconductivity values were lower at the downstream site, 

where the deepest sample collected had a value similar to 

that of the paleosols beneath Oro Grande Wash. Additional 

clay layers may occur at greater depths within the unsaturated zone at Quail Wash (fig. 4).

Recharge Processes

For the purposes of this discussion, recharge has been 

divided into areal and focused recharge. Areal recharge 

occurs from direct infiltration of precipitation or snowmelt. 

Focused recharge occurs in areas, such as stream channels, 

where precipitation and subsequent runoff collects, however 

briefly, after storms. This study describes focused recharge 

from small intermittent streams present within the western 

Mojave Desert. Recharge from the Mojave River is discussed 

in a regional context to determine if the aggregated recharge 

from many small sources is as large as recharge from this 

single large source.
166 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

Areal Recharge

Previous studies have shown that direct infiltration of 

precipitation to depths below the root zone and subsequent 

ground-water recharge do not occur in many alluvial valley 

floors at rates significant for water supply through the thick 

unsaturated zones characteristic of arid areas in southern California (Prudic, 1994; Izbicki and others, 2000b, 2002) and in 

the southwestern United States (Phillips, 1994; Prudic, 1994). 

Analyses of core material collected from five boreholes as 

deep as 30 m at control sites away from study washes shows 

that the unsaturated zone underlying the Mojave Desert is very 

dry, with a median volumetric water content of 0.04 (Izbicki 

and others, 2000a). Volumetric water contents in coarsegrained material from some boreholes were less than 0.01. 

Water potentials, a measure of how tightly water is held within 

a material, were highly negative. Analysis of total potential 

(matric potential plus elevation potential) shows that gravity 

drainage does not occur at many of these sites and that the 

potential is for water to move upward as vapor towards shallower depths where soluble salts have accumulated beneath the 

surface (Izbicki and others, 2000a,b, 2002). The most negative 

water potentials, between –11,000 and –14,000 kPa, at depths 

of about 10 m, were associated with overlying high chloride 

concentrations (approaching 200 mg/g of alluvium) at depths 

between 5 and 10 m (site OGF, fig. 7). Because of its high 

solubility chloride, would move readily with infiltrating water 

if areal recharge were occurring (Allison and Hughes, 1978; 

Allison and others, 1985, 1994). Dry conditions and chloride 

accumulations in the unsaturated zone suggest that water is not 

infiltrating to greater depths and that areal recharge does not 

occur in the western Mojave Desert under present-day climatic 

conditions (Izbicki and others, 2000 and 2002).

Focused Recharge From Intermittent Streams

Analysis of core material from boreholes as deep as 

200 m at 10 sites underlying Oro Grande Wash, Sheep 

Creek Wash, and Quail Wash shows that the unsaturated 

zone is much wetter beneath the washes than in the surrounding alluvial fans. Volumetric water contents are as 

high as 0.26 and matric potentials in many profiles are near 

zero (site UOGW and LOGW-1, fig. 7; Izbicki and others, 

2000a). Calculations of total potential (matric potential plus 

gravitational potential) show downward movement of water 

under the influence of gravity at many of these sites (Izbicki 

and others, 2000b, 2002). Chloride concentrations in the 

alluvium are low, typically near 1 mg/g of alluvium, at sites 

where infiltration is sufficiently large for water to move 

below the root zone and ultimately recharge the underlying 

water table. Chloride has accumulated at depths of about 7 

m at sites beneath the downstream reaches of Sheep Creek 

Wash (LSCW site, fig. 7) and Quail Wash (Nishikawa and 

others, 2005) suggesting that infiltration is not sufficient for 

water to move below the root zone and recharge the underlying water table along these stream reaches.

The following discussion examines the specific factors 

that control ground-water recharge, such as streamflow availability, infiltration of streamflow, deep infiltration below the 

root zone, and the movement of the water through the unsaturated zone into the underlying water table.

Streamflow Availability

Continuous-record stream gaging is the traditional 

method of assessing streamflow availability. The difference 

in flow between upstream and downstream gages can be used 

to estimate losses along stream reaches and infer infiltration 

losses into the streambed. However, stream gages are often 

impractical in desert settings because of the expense associated with the measurement of infrequent flows in channels 

that may scour or change course during streamflow. In addition, flows in some desert washes, although brief in duration, 

may be large in magnitude and destructive—precluding the 

installation of expensive monitoring equipment near stream 

channels. As a result of these limitations, with the exception 

of the perennial reach of Big Rock Creek near the mountain 

front, streams studied as part of this project were ungaged and 

alternate methods were used to assess streamflow availability 

for infiltration and ground-water recharge.

Streamflow availability was assessed by using streambed temperature data to estimating the frequency of days 

that had flow for study reaches along Oro Grande Wash, 

Sheep Creek Wash, and Big Rock Creek Wash between July 

1998 and June 2000. Streambed temperature data also were 

collected along Quail Wash between October 2000 and July 

2003. Streambed temperature data were collected by using 

inexpensive thermistors, equipped with internal data loggers, buried at shallow depths (10–20 cm) in the streambed 

(Constantz and Thomas, 1996; fig. 8). In most cases, the 

streambed temperature data were compared with similar data 

collected from instruments burried outside the stream channel, and streamflow was inferred from the difference between 

the two records. In some cases the presence of streamflow 

was inferred from the absence of daily temperature changes 

during streamflow. The streambeds were marked with paint 

to provide visible evidence of flow between site visits. 

Available precipitation and air temperature data from nearby 

weather stations, and streamflow in nearby gaged streams 

(fig. 1) also were used to constrain the interpretations. The 

approach assumes that certain changes in streambed temperature are caused by streamflow and works well in winter-dominated precipitation regimes or in streams having sustained 

flows from winter snowmelt that last from several days to 

several weeks (Constantz and Thomas, 1996, 1997).

Sustained flows lasting for more than several days did 

not occur along most fan and valley-floor reaches of Oro 

Grande Wash, Sheep Creek Wash, or Quail Wash during the 

study periods, and, except for Big Rock Creek, flows lasting 

for more than a few days were rare—even near the mountain 

fronts (fig. 9). An example of streambed temperature changes 

resulting from streamflow during winter runoff is shown for 
Recharge Processes 167

    

     

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Figure 7. Water content, water potential, chloride, and tritium concentrations at representative sites in the 

unsaturated zone in an interchannel area (OGF), and beneath an intermittent stream (UOGW, LOGW-1, LSCW), 

western Mojave Desert study area, southern California. Unit designators are as follows: water content—cubic 

meters of water per cubic meter of bulk sediment (m3

/m3); chloride [concentration]—micrograms of chloride per 

gram of pore water (μg/g); water potential [per volume of pore water]—kilopascals (kPa). Figure 1 shows site 

locations.
168 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

Figure 8. Streambed 

temperature site along 

Sheep Creek Wash near 

borehole USCW, western 

Mojave Desert, southern 

California. Inset shows 

close-up of temperature 

sensor. Figure 1 shows the 

site location.

the upstream part of the study reach along Sheep Creek Wash 

from February 17 to 27, 2000 (fig. 10). Streamflow occurred 

twice during this period as a result of runoff from precipitation and snowmelt, although the duration of each flow was less 

than 2 days. The duration of streamflow inferred on the basis 

of temperature data for sites farther downstream was progressively less with increasing distance from the mountain front. 

Flow along Sheep Creek Wash during this period was confirmed by examination of the streambed.

Uncertainty about the occurrence of streamflow is larger 

for summer flows than winter flows because the duration of 

summer flows may be short and the streambed temperature 

change associated with summer flows are often small. An 

example of streambed temperature changes resulting from 

a brief flow after a summer thunderstorm is shown for Oro 

Grande Wash from July 5 to 11, 1999 in figure 11. Visits to 

the site and examination of the streambed confirmed that flow 

occurred during this period, but it was uncertain as to which 

changes in streambed temperature actually represented flow. 

Streambed temperature changes that occurred on July 10 and 

11 were not interpreted as streamflow on the basis of numerical-model simulations that suggest that similar changes could 

result solely from infiltration of precipitation (Johnson and 

Izbicki, in review), although streamflow may have occurred.

The number of days having unexplained streambed temperature changes and streambed temperature changes interpreted as streamflow along Oro Grande Wash, Sheep Creek 

Wash, and Big Rock Creek Wash are shown in figure 12. 

The difference between the two lines in the graphs illustrates 

the magnitude of uncertainty associated with the interpretation of streamflow frequency in these channels. Although 

the magnitude of the uncertainty was nearly as great as the 

magnitude of the estimated flow frequency along much of 

Oro Grande Wash and Sheep Creek Wash, spatial patterns 

are apparent in the data.

Oro Grande Wash had the lowest estimated annual 

streamflow (table 1) and the lowest frequency of streamflow. 

Oro Grande Wash is no longer connected to the mountain 

front and flows only as a result of runoff from the surrounding 

alluvial fan deposits. Field observations and temperature data 

show that flows in Oro Grande Wash were brief in duration, 

typically lasting only an hour or less; therefore, a flow frequency of 0.05 days per year having flow probably represents 

a cumulative flow duration closer to 18 hours of flow rather 

than 18 days of flow (365 days per year times 0.05 days per 

year having flow).

Frequency of flow in Sheep Creek Wash and Big 

Rock Creek Wash was greater near the mountain front and 

decreased downstream as streamflow decreased—presumably due to infiltration into the unsaturated zone. The magnitude of the uncertainty associated with the technique was less 

near the mountain front where streamflow was more frequent 

and sustained for longer periods than farther downstream. 

This is particularly true for Big Rock Creek Wash where 

flow near the mountain front was perennial. 

Farther from the mountain front, the flow frequency 

along Oro Grande Wash was similar to the flow frequency 

along both Sheep Creek Wash and Big Rock Creek Wash, 

except that small increases in flow frequency were observed 

along the downstream, urbanized reaches of Oro Grande 

Wash. Izbicki and others (2000b) inferred increased streamflow along this reach as a result of urbanization on the basis 

Figure 9. Streamflow in Oro Grande Wash 

near VVWD, western Mojave Desert, southern 

California (January 28, 2001). Duration of flow 

from winter snowmelt was about 1 hour. Figure 1 

shows the site location.
Recharge Processes 169







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Figure 10. Precipitation, streambed temperature, control temperature (collected outside of streambed), and 

inferred duration of streamflow along Sheep Creek Wash, western Mojave Desert, southern California, February 

17–27, 2000. Figure 1 shows the site location.

       

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Figure 11. Precipitation, streambed temperature, control temperature (collected outside of streambed), and inferred 

duration of streamflow along Oro Grande Wash, western Mojave Desert, southern California, July 5–12, 1999. Figure 1 shows 

the site location.
170 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

/RO'RANDE7ASH



































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Figure 12. Frequency of temperature anomalies and frequency of 

days interpreted to have flow as a function of distance downstream 

in Oro Grande, Sheep Creek Wash, and Big Rock Creek Wash in the 

western Mojave Desert, southern California, July 1, 1998, to June 18, 

2000. Figure 1 shows site locations.

of water content and chloride data collected from the unsaturated zone underlying the wash (LOGW-1, fig. 7).

Frequency and duration of flow are direct measures 

of streamflow available for infiltration and are important 

measures of the potential for ground-water recharge along 

a given stream reach. In principle, if the frequency and 

duration of flow are known with suitable precision, annual 

infiltration into the streambed can be calculated by multiplying the cumulative duration of individual streamflows by 

the hydraulic conductivity and wetted area of the streambed 

material, assuming a downward hydraulic gradient of 1. In 

practice, this approach was not used because it was not possible to measure the cumulative flow duration with suitable 

precision on the basis of streambed temperature data. Furthermore, the hydraulic properties of streambed material are 

not precisely known and may change during flow as a result 

of scour or deposition. Therefore, an indirect method was 

used to estimate infiltration from streamflow.

Infiltration From Streamflow

Continuous water-potential and temperature data collected from an instrumented borehole in the streambed along 

Oro Grande Wash illustrate infiltration of streamflow during the rainy season (fig. 13). The data are from instruments 

located about 6 m below the streambed. The instruments are 

especially responsive to the infiltration of water from the 
Recharge Processes 171

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Figure 13. Temperature and matric potential about six meters below the streambed at site VVWD along 

Oro Grande Wash, western Mojave Desert, southern California. Figure 1 shows the site location.

stream because they are located above a 2-m thick clay layer 

that impedes the downward movement of water at the site.

As many as 16 distinct subsurface temperature changes, 

possibly associated with individual streamflows and subsequent infiltration of cold water along the wash, can be identified on the basis of the temperature data beneath Oro Grande 

Wash (fig. 13). The number and brief duration of these flows 

corresponds with the number of flows expected from frequency and duration data estimated on the basis of shallow 

streambed temperature data for this reach of Oro Grande Wash 

(fig. 8). Summer flows are less apparent in the data because 

temperature changes associated with summer streamflows are 

small. The cumulative infiltration from the rainy-season flows 

results in the increase in moisture apparent as less negative 

water potentials between January 24 and February 12, and 

between March 26 and April 15, 2002 (fig. 9). Changes in 

temperature and water potential at the site are dampened with 

depth, and although small seasonal changes in temperature 

of several tenths of a degree Celsius are apparent at depths as 

great as 26 m, water-potential data dampen to a constant value 

at the next instrument about 8 m below land surface. 

The cumulative infiltration from rainy-season streamflows also results in a cooling of the unsaturated zone beneath 

the streambed in comparison with the surrounding material. 

This was measured as the difference in temperature between 

small-diameter (50 mm) air-filled access tubes at selected sites 

and nearby access tubes along Oro Grande Wash and Sheep 

Creek Wash between October, 1996, and September, 1997 

(Izbicki and Michel 2002; fig. 14) and between October 2000 

and July 2003 along Quail Wash. Comparison of temperature 

data (fig. 14) with chloride and data (fig. 7) shows that at 

sites such as UOGW and LOGW, where the temperature data 

suggest that a large amount of infiltration occurs, chloride is 

absent beneath the wash and tritium is present at great depths. 

In contrast, at sites, such as LSCW, where the temperature 

data suggest that only a small amount of infiltration occurs, 

chloride is present near the bottom of the root zone (about 7 

m) and tritium is present only near the surface, typically about 

1 m below land surface.

If the thermal properties of the underlying material can be 

estimated and one-dimensional downward movement of heat 

and water are assumed, temperature data can be converted into 

estimates of infiltration by using an approach described by 

Izbicki and Michel (2002). Numerical models, such as VS2DT 

(Lappala and others, 1987), also can be used to estimate 

infiltration (Kulongoski and Izbicki, 2008). The modeling 

approach incorporates advective and conductive movement of 

heat in two-dimensions and has the additional advantage of 

incorporating temporal changes in the distribution of infiltration. This information is important in areas where streamflow 

and subsequent infiltration do not occur every year. Hydraulic 

and thermal-property data, and details of model construc-
172 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California $%04().-%4%23"%,/7,!.$352&!#%















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Figure 14. Temperature in small-diameter access tubes in intermittent streams and respective control sites 

along Oro Grande and Sheep Creek Washes in the western Mojave Desert, southern California, 1997–99 (modified 

from Izbicki and Michel, 2002). Figure 1 shows site locations.
Recharge Processes 173

tion used to estimate infiltration along selected study reaches, 

are discussed by Kulongoski and Izbicki (2008). Simulation results at selected sites show that the effect of different 

recharge rates and frequency of infiltration on the temperature 

profiles at selected sites along study washes (fig. 15).

The average infiltration rate at each site was estimated as 

the modeled infiltration rate divided by the number of years 

since infiltration occurred. The average infiltration rate was 

greatest along the upper reaches of Sheep Creek Wash near the 

mountain front. Although the bed of Sheep Creek Wash near 

the mountain front consists primarily of cobbles, instantaneous 

infiltration rates measured in this reach, by using a double-ring 

infiltrometer (table 2), were lower than rates measured along 

Oro Grande Wash; however, the average annual infiltration 

rate is greater along Sheep Creek Wash near the mountain 

front because the frequency of flow is greater along this reach 

(fig. 12). Model results showed that infiltration did not occur 

every year along most study reaches in sufficient magnitude 

to have a measurable effect on the subsurface temperature 

profile. However, infiltration was most consistent along the 

downstream reaches of Oro Grande Wash and Quail Wash. 

Runoff along these reaches has increased in recent years as a 

result of upstream urbanization. Infiltration was lowest along 

the downstream reach of Sheep Creek Wash; streamflow along 

this reach occurs infrequently for brief periods of time and the 

silty streambed along this reach has low permeability limiting 

the infiltration of streamflow.

Average annual infiltration along the study reaches of 

Oro Grande Wash, Sheep Creek Wash, and Quail Wash was 

estimated as the average infiltration rate times the width 

of the wash times the length of the wash reach between 

measurement points. Average annual infiltration along the 

study reaches was greater along Sheep Creek Wash than 

along Oro Grande Wash and Quail Wash (table 2). Along 

all three reaches, average annual infiltration was about 

20 percent of the estimated annual streamflow, and more 

water is transmitted through the reach as surface flow than 

infiltrates into the streambed. Water infiltrated into the 


 
 
  
 
 
  
 
 
 

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INFILTRATION

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INFILTRATION

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INFILTRATION

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%VERYYEAR

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Figure 15. Measured and simulated temperature differences between selected wash sites and nearby 

control sites along Oro Grande (UOGW and LOGW-1) and Sheep Creek (LSCW) Washes, western Mojave 

Desert, southern California. Figure 1 shows site locations.
174 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

streambed may be transpired by plants along the stream 

channel or may infiltrate to depths below the root zone and 

ultimately become ground-water recharge.

Movement of Infiltrated Streamflow Below 

the Root Zone

Infiltration of streamflow below the root zone, also 

known as deep infiltration, was identified on the basis of 

chloride data in selected reaches of Oro Grande Wash, 

Sheep Creek Wash, and Quail Wash. As previously discussed, chloride is a tracer of the movement of water though 

unsaturated zones in arid environments. In areas where deep 

infiltration, and subsequent ground-water recharge do not 

occur, chloride in precipitation or dry deposition, may accumulate to high concentrations 5 to 10 m below land surface 

(fig. 7). In areas where recharge occurs, chloride—being 

highly soluble—will move with infiltrating water to depths 

below the root zone and ultimately to the underlying water 

table (Allison and Hughes, 1978; Allison and others, 1985, 

1994; Prudic, 1994; Phillips, 1994).

The upstream site along Oro Grande Wash, UOGW 

(fig 7), is an example of a site where chloride is not present 

in the unsaturated zone underlying the wash, and groundwater recharge occurs under present-day climatic conditions 

(Izbicki and others, 2002). The downstream site along Oro 

Grande Wash, LOGW, is an example of a site where chloride 

that accumulated in the subsurface has been mobilized by 

increased infiltration of streamflow resulting from upstream 

urbanization (Izbicki and others 2000b, 2002). As discussed 

previously, streamflow along this reach of Oro Grande Wash 

has increased in recent years because of urbanization. Similar 

effects were observed along reaches of Sheep Creek Wash 

where levees have controlled streamflow, and subsequent infiltration, that under predevelopment conditions were distributed 

over time across the surface of the fan but are now restricted to 

a few active channels (Izbicki and others, 2002).

If water infiltrated at land surface is completely consumed by plants along a stream reach, chloride will accumulate at the base of the root zone. In these settings, although 

streamflow and infiltration occur, deep infiltration and subsequent ground-water recharge do not occur. The downstream 

site along Sheep Creek Wash, LSCW, is an example of a site 

where chloride has accumulated near the base of the root 

zone beneath the wash (Izbicki and others, 2002). Temperature data collected at this site suggest that streamflow and 

infiltration, while not occurring every year, average about 

0.7 m/yr. This value may represent a threshold below which 

deep infiltration does not occur. Assuming that deep infiltration does not occur along reaches where chloride has accumulated, estimates of infiltration along Oro Grande Wash 

and Sheep Creek Wash can be reduced to provide an estimate 

of deep infiltration, and subsequent ground-water recharge 

(table 2). The threshold for deep infiltration is probably less 

in wider channels having less vegetation, or in channels composed of more permeable material.

Deep Movement to the Water Table

In many studies deep infiltration is presumed to ultimately become ground-water recharge because there are few 

processes that will remove water from the unsaturated zone 

other than plant roots, and because data from deeper depths 

are difficult and expensive to collect. However, before infiltrated water becomes ground-water recharge it must move 

through the unsaturated zone to the underlying water table. 

In the Mojave Desert the unsaturated zone may be as much 

as several hundred meters thick in some places and may be 

composed of many different layers having different hydraulic properties that ultimately control the rate of downward 

movement, lateral spreading, and flow of water through the 

unsaturated zone.

Rate of downward movement—The rate of downward 

movement of water through the unsaturated zone underlying 

Oro Grande Wash and Sheep Creek Wash was estimated on 

the basis of tritium data. Tritium is a radioactive isotope of 

hydrogen having a half-life of about 12.3 years. Although 

tritium is naturally occurring, the atmospheric testing of 

nuclear weapons beginning in 1952 increased its presence 

in the environment. Tritium concentrations reached a peak 

in about 1962 and decreased after the atmospheric testing of 

nuclear weapons ended (Michel, 1976). For the purpose of 

this paper, water in the unsaturated zone having measurable 

tritium was interpreted as water infiltrated after 1952 and 

the highest tritium concentrations were interpreted as water 

infiltrated in about 1962.

Tritium is not present in the unsaturated zone away from 

active stream channels at depths below the root zone where 

soluble salts have accumulated (fig. 5). In contrast, tritium 

was present at depths in excess of 30 m beneath Oro Grande 

Wash near Cajon Pass (UOGW and MOGW) and Sheep 

Creek Wash (USCW) near the mountain front. Downward 

rates of movement for infiltrating water at these sites must 

be at least 1.5 m/yr. Smaller rates of movement ranging 

from 0.8 to 0.3 m/yr were estimated for sites farther downstream where deep infiltration occurs (Izbicki and others, 

2002). Given these rates of movement, and an unsaturated 

zone ranging from 130 m to more than 300 m thick near the 

mountain front, travel times of several hundred years may 

be required for infiltrating water to reach the water table 

beneath the sites (Izbicki and others, 2002). Given these long 

travel times, infiltration from infrequent streamflow dampens to a constant recharge rate by the time water reaches the 

water table. In settings such as the western Mojave Desert, 

recharge from small streams, such as Oro Grande Wash, 

Sheep Creek Wash, and Quail Wash, is not likely to be 

affected by short-term climatic cycles, such as El Niño or the 

Pacific Decadal Oscillation, even though infiltration at the 

streambed surface may greatly increase during these periods.

Lateral spreading—As infiltrated water moves downward 

through the unsaturated zone, it will spread laterally away 

from the wash. Lateral spreading decreases the flux and the 

rate of downward movement of the water (Izbicki and oth-
Recharge Processes 175

10 YEARS 

80 YEARS 

60 YEARS 

100 YEARS 

0 

DEPTH, IN METERS BELOW LAND SURFACE

0 

200 160 120 80 40 0 

DISTANCE, IN METERS 

0 

20 

40 

60 

20 

40 

60 

20 

40 

60 

0 

20 

40 

60 

40 YEARS 

0 

0 

20 

40 

60 

20 

40 

60 

20 YEARS 

Oro Grande Wash 

Reworked 

alluvium 

lithology not differentiated 

Victorville fan deposits– 

Wetted area 

EXPLANATION 

ers, 2000b; Nimmo and others, 2002). Lateral spreading of 

infiltrating water is controlled by the distribution and hydraulic properties of thin, often areally extensive, clay layers in the 

subsurface (Izbicki, 2002). These clay layers are believed to be 

soil horizons that developed during intervals when deposition 

was not occurring on the alluvial fan and were subsequently 

buried when deposition resumed. Given an infiltration rate of 

1.3 m/yr applied to a 3-m wide wash, Izbicki (2002) simulated 

the movement of water through the heterogeneous unsaturated 

zone underlying Oro Grande Wash (fig. 16) to illustrate the 

effect of clay layers on the movement of water through the 

unsaturated zone. These simulations matched both the downward rate of movement of the infiltrating water calculated 

from tritium data and the lateral spreading of water measured 

in the unsaturated zone along a cross section perpendicular to 

the wash (Izbicki, 2002). Results were consistent with thin areally extensive clay layers from buried soils in the unsaturated 

zone rather than less extensive fine-grained fluvial deposits.

Flow of water through the unsaturated zone—The 

simulated movement of water shown in figure 16 assumes 

movement through the unsaturated porous media governed by 

Darcy’s Law. Changes in the isotopic composition of water 

vapor after streamflow (Izbicki and others, 2000) show rapid 

movement of a small amount of water through preferential 

pathways, such as small cracks, in the unsaturated zone. If 

preferential flow occurs, some water may move in advance of 

the main wetting front and reach the water table faster than 

expected on the basis of Darcy flow.

Movement of water through the unsaturated zone was 

evaluated on the basis of a large-scale infiltration test at the 

VVWD site (fig. 1) along Oro Grande Wash near Victorville. 

Between October 1 and December 15, 2002, almost 

190,000 m3 of ground water was pumped from nearby public 

supply wells into a 0.4 ha pond and allowed to infiltrate into 

the unsaturated zone (fig. 17). An additional 72,000 m3 was 

applied to the pond between February 10 and March 25, 2002. 

Measurement of infiltration from the pond provided a unique 

opportunity to evaluate the physical processes that control 

movement of water through a 130-m-thick, heterogeneous 

unsaturated zone, in the same manner that aquifer tests provide 

data on the physical movement of water through saturated 

aquifer material.

The site was selected because of its potential for artificial recharge resulting from its position on the alluvial 

fan overlying permeable material at the water table. Farther 

downslope the alluvial fan deposits are finer-grained—potentially impeding the downward movement of applied water 

through the unsaturated zone. Farther upslope the deposits are 

coarser grained but thicker; although water is likely to move 

downward through the unsaturated zone, permeable deposits 

pumped for water supply are not present at the water table in 

this area (fig. 18). The downward movement of water beneath 

the pond was monitored at a borehole instrumented with 

advanced tensiometers that measure both positive (saturated 

conditions) and negative (unsaturated conditions) pressure, 

and heat-dissipation probes that measure negative pressures. 

Figure 16. Simulated movement of water through a thick 

unsaturated zone having areally extensive clay layers, Oro 

Grande Wash, western Mojave Desert, southern California 

(modified from Izbicki, 2002).
176 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

Figure 17. Photograph of artificial recharge pond along Oro 

Grande Wash, western Mojave Desert, southern California. 

Flow from standpipe is about 50 liters per second.

Sequential electromagnetic logs were collected through a 

50-mm-diameter access tube within the borehole to monitor 

the movement of applied water between instruments within the 

borehole and confirm tensiometer and heat-dissipation probe 

data. The borehole was sealed with low-permeability grout, 

except for short intervals near the instruments, by using procedures described in Izbicki and others (1995, 2000b, 2002) to 

minimize flow through the borehole during the infiltration test.

Results of data collection show rapid downward movement of water infiltrated from the pond. Changes in matric 

potential measured by using heat-dissipation probes between 

6.7 and 26.2 m below land surface showed that on the basis of 

the arrival of the wetting front the rate of downward movement 

approached 1 m/d in October 2002 (fig.19). Slower rates of 

movement were recorded later in the test, in part because infiltrated water spread laterally away from the pond and because 

water was not infiltrated continuously from the pond.

Saturated conditions were measured beneath the pond in 

the tensiometer 6.4 m below land surface. This tensiometer is 

located above a fine-grained, clay-rich layer that impeded the 

downward flow and contributed to the lateral movement of 

water in the unsaturated zone (fig. 19). Water drained from this 

zone during periods when water was not present in the pond. 

Background data collected prior to the application of water 

from the pond showed that saturated conditions also developed 

on this clay layer from natural infiltration of streamflow at this 

site—although less water accumulated on the clay layer than 

during the infiltration test.

Saturated conditions also developed on a clay layer 84.7 m 

below land surface by late January 2003. Other instruments and 

geophysical log data show that at this time the main wetting 

front was still less than 60 m below land surface, and saturated 

conditions at this depth can only be explained by rapid movement of water, ahead of the main wetting front, through preferential pathways, such as cracks and large interconnected pore 

spaces. Increases in pressure between October and January are 

the result of increased air-pressure at this depth as air in the 

Figure 18. Subsurface geologic conditions in area of artificial 

recharge, Oro Grande Wash, southern California. Arrows represent 

recharging water. 

unsaturated zone was compressed by the downward-moving 

water, and from the cumulative weight of the infiltrated water 

on subsurface material. 

Matric-potential data from heat-dissipation probes also 

show that small amounts of water moved ahead of the main 

wetting front through preferential pathways at rates approaching 2 m/d. For example, increases in pressure were recorded in 

the heat-dissipation probe at 53.6 m prior to the arrival of the 

main wetting front in February 2003 (fig. 19). This instrument, 

unlike the tensiometers, is not sensitive to increases in air pressure or the cumulative weight of the water and the measured 

changes in matric potential must represent the arrival of a 

small amount of water at the instrument prior to the arrival of 

the main wetting front. 

Flow of water through preferential pathways was predicted for this site on the basis of changes in the isotopic composition of water vapor in the unsaturated zone after streamflow (Izbicki and others, 2000b). Although measurable, the 

amount of water that moved through preferential pathways in 

the unsaturated zone must under natural conditions have been 

small and probably did not significantly contribute to natural 

recharge at this site. However, this process may be important 

in areas where storage of hazardous waste in the unsaturated 

zone has been proposed.

Rates of movement between instruments and the position 

of the wetting front underlying the pond were confirmed on 

the basis of sequential electromagnetic logs (fig. 20). Increases 

in electromagnetic conductivity reflect increases in moisture 

content and decreases in electromagnetic conductivity reflect 

decreases in moisture content as infiltrated water moved 

through the unsaturated zone.

On the basis of electromagnetic log data, saturated conditions may have developed above coarse-grained layers in the 

unsaturated zone. This can occur because more pressure is 

required for water to enter the larger pore spaces between 

coarser-grained material than the smaller pore spaces in 

finer grained material. Electromagnetic logs done between 

California

Aqueduct

Victorville Fan

Deposits

Impermeable Caliche

Ancestral Mojave River Deposits

Water table

Thicker Coarser-Grained Unsaturated

Zone

Less Permeable Saturated Zone

More Permeable

Thinner

Finer-Grained Unsaturated

Zone

Oro Grande

Wash Recharge

pond
Recharge Processes Recharge Processes 177

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METERS

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Figure 19. Response of selected instruments in the unsaturated zone to artificial recharge from a 

constructed pond near Oro Grande Wash (site VVWD), western Mojave Desert, southern California. Figure 1 

shows the site location.

November 15, 2002, and December 4, 2002 (fig. 20), show 

that saturated conditions may also have developed above a 

coarse-grained layer at a depth near 30 m. Saturated conditions 

also occurred above a coarse-grained layer near 45 m between 

December 4 and December 22, 2002. After the entry pressure for 

water to enter the coarse-grained deposits was exceeded, water 

drained rapidly through the material at both depths (fig. 20). 

Electromagnetic log data also show redistribution of 

water in the unsaturated zone between December 22, 2002, 

and May 6, 2003. After December 15, 2002, when less water 

was infiltrated from the pond, water in the upper part of the 

unsaturated zone continued to move downward under the 

influence of gravity; however, the rate of downward movement 

was significantly less.
178 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California $%04().-%4%23"%,/7,!.$352&!#%

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The results of the large-scale infiltration experiment 

show that the movement of water through thick, heterogeneous unsaturated zones is complex. Saturated conditions may 

develop above both fine-grained and coarse-grained layers, 

reducing the rate of downward movement of water. Saturated 

flow in these layers may increase the lateral spreading of 

water, further reducing the rate of downward movement of 

water. Although small amounts of water may move ahead 

of the main wetting front, after the water source is removed, 

downward movement continues at reduced rates as water is 

redistributed throughout the unsaturated zone. Given the time 

of travel and complex movement of water in thick, heterogeneous unsaturated zones, it may be unrealistic to assume 

that water infiltrated to depths below the root zone becomes 

ground-water recharge—especially in geomorphic settings, 

such as Sheep Creek Wash and Quail Wash, where channel 

abandonment processes on active alluvial fans may effectively 

strand water in the unsaturated zone above the water table.

Regionalization of Results

At the beginning of this study, it was unclear if the quantity of water infiltrated and recharged from a single large source, 

such as the Mojave River, was greater than the total quantity of 

water infiltrated from the many smaller sources, such as Oro 

Grande Wash, Sheep Creek Wash, Big Rock Creek Wash, Quail 

Wash and other small streams draining the San Gabriel, San 

Bernardino, and Little San Bernardino Mountains. Stamos and 

others (2001) estimated that annual recharge along the Mojave 

River averaged 47.6 hm3 between 1930 and 1990. This value 

is much greater than the estimated infiltration and subsequent 

recharge (deep infiltration) from Oro Grande Wash, Sheep 

Creek Wash, and Quail Wash, which totals less than 0.8 hm3

(table 2). A very large number of small streams, each contributing their small amount of recharge, would be required for the 

aggregated recharge from these sources to equal the recharge 

from a single large source such as the Mojave River. 

Figure 20. Sequential electromagnetic logs showing movement of water through the upper 75 m of the 

120-m-thick unsaturated zone underlying an artificial-recharge pond near Oro Grande Wash, western Mojave 

Desert, southern California.
Regionalization of Results 179

The rank-order distribution of streams draining the 

north-facing slope of the San Gabriel and San Bernardino 

Mountains, and east-facing slope of the Little San Bernardino 

Mountains is shown as a function of drainage area and stream 

order in figure 21 and table 3. The drainage area of each 

stream was calculated as the area upstream from the mountain 

front. A first-order stream is a stream having no tributaries, a 

second-order stream is formed at the confluence of two firstorder streams, a third-order stream is formed at the confluence 

of two second-order streams, and so forth. The smallest area 

considered was 0.9 km2. The largest basin considered was the 

headwaters of the Mojave River (including the West Fork of 

the Mojave River and Deep Creek), a fifth order stream draining 542 km2

 in the San Bernardino Mountains west of Cajon 

Pass. Oro Grande Wash (and other small streams near Cajon 

Pass) are not shown on figure 21 because they are not connected to the mountains as a result of erosion near Cajon Pass.

Quail Wash and Sheep Creek are among the larger streams 

draining the mountains. Results of this study show that deep 

infiltration and subsequent ground-water recharge from these 

streams are highly variable—ranging from 0.1 hm3

 for Quail 

Wash to 0.5 hm3 (table 2) for Sheep Creek Wash—and not 

well-correlated to drainage area size (indicating heterogeneity of precipitation). In the case of Quail Wash, the second 

largest stream in the study area, much of the water that 

infiltrates may not reach the water table. Given that average 

annual recharge in the Mojave River has been estimated to be 

about 47.6 hm3 (Stamos and others, 2001), there simply are 

not enough of the smaller streams to equal the large amount 

of recharge from a single large source such as the Mojave 

River. The smaller, more numerous first- and second-order 

streams, in aggregate, account for less than 20 percent of the 

total mountain drainage area. Furthermore, potential runoff, 

infiltration, and subsequent ground-water recharge from such 

sources are inherently smaller because low-order streams 

drain lower altitudes where precipitation is lower (due to 

orographic effects) than the higher altitudes drained by highorder streams. 

Streams such as Sheep Creek are locally important 

sources of ground-water recharge. However, even for these 

relatively large secondary streams, the estimated recharge 

from infiltration that travels through the unsaturated zone 

is small compared to estimates made by Stamos and others 

(2001) by fitting a regional ground-water flow model. This difference suggests that most of the recharge to the regional aquifer in this area occurs as a result of infiltration of streamflow 

through coarse alluvium near the mountain front. Recharge in 

this fashion does not distribute water rapidly to large distances 

from the mountain front.

The isotopic composition of ground water was used 

to confirm interpretations of the cumulative ground-water 

recharge from small intermittent streams relative to other 

sources in the study area, especially the Mojave River. Isotopic 

data collected as part of this study included the stable isotopes 

of oxygen and hydrogen (oxygen-18 and deuterium, respectively), tritium, and carbon-14. These results are summarized 































0%2#%.4'2%!4%24(!./2%15!,4/



























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.

-OJAVE2IVER

1UAIL7ASH

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3HEEP#REEK

.

1UAIL7ASH

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3HEEP#REEK

.

.

.

3TREAM

/RDER









Figure 21. Rank-order distribution of selected basins on the 

north slope of the San Gabriel, San Bernardino, and Little San 

Bernardino Mountains, southern California.

below. More detailed discussions are presented in Izbicki and 

others (1995), Izbicki (2004), and Izbicki and Michel (2004).

Oxygen-18 and deuterium are naturally occurring stable 

isotopes of oxygen and hydrogen, respectively. Oxygen-18 

and deuterium abundances are expressed as ratios in delta 

notation (δ) as per mil (parts per thousand) differences relative to the standard known as Vienna Standard Mean Ocean 

Water (VSMOW; Gonfiantini, 1978). Because the source of 

most of the world’s precipitation is evaporation of seawater, the δ18O and δD composition of precipitation is linearly 

correlated. This relation is known as the meteoric water line 
180 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

Table 3. Drainage area of streams in the San Bernardino, 

Little San Bernardino, and San Gabriel1 Mountains, southern 

California, by stream order.

[Abbreviations: —, not applicable (population consists of one value); 

km2, square kilometers]

Stream 

order

Number of 

streams

Total drainage area,

in km2

Representative 

(50th percentile) 

drainage area,

in km2

5 1 543. —

4 7 813. 96.

3 15 519. 28.

2 40 277. 5.2

1 78 155. 1.6

1

Includes streams east of Amargosa Creek (near Palmdale) to Cajon 

Pass in the San Gabriel Mountains, and streams from Cajon Pass to 

Twenty-Nine Palms in the San Bernardino and Little San Bernardino 

Mountains.

(Craig, 1961). The δ18O and δD composition of ground water 

relative to the meteoric water line and relative to the isotopic 

composition of water from other sources is an indication of the 

source and movement of the ground water. For example, water 

that condensed at cooler temperatures associated with higher 

altitudes has less of the heavier isotopes and more negative d

values than water that condensed at warmer temperatures associated with lower altitudes. In contrast, water than has been 

partly evaporated prior to recharge is enriched in the heavy 

isotopes relative to its original composition and plots to the 

right of the meteoric water line.

Orographic effects near Cajon Pass between the San 

Gabriel and San Bernardino Mountains allow air masses 

laden with moisture from the Pacific Ocean to enter the 

Mojave Desert during the winter rainy season and precipitate without uplift over the higher altitudes in the mountains 

(Izbicki, 2004). Winter precipitation near Cajon Pass gives 

rise to streamflow in the Mojave River, the largest stream in 

the study area. Because it condensed at lower altitudes and 

warmer temperatures, precipitation near Cajon Pass is isotopically heavier than precipitation that condensed over the 

mountains. Recharge from infiltration of streamflow along 

the Mojave River has resulted in a large body of isotopically 

heavy ground water extending for more than 100 km into 

the Mojave Desert (fig. 22). The isotopically heaviest water 

sampled in the study area is to the west of the Mojave River 

results from increased precipitation near the pass that has 

not been fractionated by orographic uplift over the mountains and subsequent runoff and infiltration of streamflow 

in Oro Grande Wash and other similar washes near the pass 

(Izbicki and others, 1995). These data demonstrate that, 

although the quantity of water from these sources is small, 

it is locally important. Similar processes have resulted in 

isotopically heavy ground water in the eastern part of the 

study area along Pipes Wash and in Yucca Valley near 

San Grogonio Pass (fig. 22), and along the western edge 

of Antelope Valley where the altitudes of the San Gabriel 

Mountains are lower (Smith and others, 1992). Precipitation, 

streamflow, and subsequent ground-water recharge associated with precipitation in low-altitude passes is different 

from conditions in most areas in the arid southwestern 

United States where precipitation, streamflow, and subsequent ground-water recharge are associated with higher 

altitudes in the mountains. This difference results from the 

cyclonic circulation of winter precipitation from west to east 

and proximity of the study area to the Pacific Ocean.

As previously discussed, tritium is a radioactive isotope 

of hydrogen having a half-life of 12.3 years. Although tritium 

is naturally occurring, the atmospheric testing of nuclear 

weapons beginning in 1952 greatly increased its presence in 

the environment. Tritium concentrations peaked about 1962 

and decreased after nearly all atmospheric testing of nuclear 

weapons ended (Michel, 1976). Tritium concentrations in 

water that infiltrated before 1952 are below detection. Water 

with detectable amounts of tritium were thus interpreted as 

water that infiltrated during or after 1952. Where a tritium 

peak was present, the peak concentrations were interpreted as 

water that infiltrated in 1962. 

Much of the water recharged along the Mojave River 

contains tritium (fig. 22) and was recharged after 1952. This 

water was distributed more than 150 km from Cajon Pass and 

the mountain front along the channel of the Mojave River by 

surface flow in the river. In contrast, only a small amount of 

recently recharged ground water containing tritium was present near Sheep Creek, Lucerne Valley, Pipes Wash, and Yucca 

Valley where small intermittent streams flow from the mountains. These data confirm that although infiltration from intermittent streams draining the San Gabriel and San Bernardino 

Mountains is locally important, especially in canyons near the 

mountain front; recent recharge from these sources is small 

and not distributed great distances by surface flow in small 

streams from the mountain front in comparison with recharge 

from a source such as the Mojave River.

Like tritium, carbon-14 also provides information on the 

age, or time since recharge, of ground water. Carbon-14 is 

a naturally occurring radioactive isotope of carbon having a 

half-life of about 5,730 years (Mook, 1980). Carbon-14 data 

are expressed as percent modern carbon by comparing carbon-14 activities to the specific activity of National Bureau 

of Standards oxalic acid: 12.88 disintegrations per minute 

per gram of carbon in the year 1950 equals 100 percent 

modern carbon. Carbon-14 was produced, as was tritium, 

by the atmospheric testing of nuclear weapons. As a result 

carbon-14 activities may exceed 100 percent modern carbon 

in areas where ground water contains tritium. Because of its 

longer half-life, carbon-14 preserves information on groundwater recharge over a longer time scale than does tritium. 

Unlike tritium, carbon-14 is not part of the water molecule, 
Regionalization of Results 181

117o00' 116o00' 

117o00' 116o00' 

Victorville 

Barstow 

Yucca

Valley

San Gabriel Mts

San Bernardino Mts

Little San Bernardino Mts

Sheep 

Creek 

Pipes 

Wash 

Morongo 

ground-water 

 basin 

Mojave River 

ground-water 

basin 

Lucerne

Valley

0 20 

KILOMETERS 

40 

117o00' 116o00' 

117o00' 116o00' 

34o

30' 

35o

00' 

Victorville 

Barstow 

Yucca

Valley

San Gabriel Mts

San Bernardino Mts

Little San Bernardino Mts

Sheep 

Creek 

Pipes 

Wash 

Morongo 

ground-water 

 basin 

Mojave River 

ground-water 

basin 

Lucerne

Valley

0 20 

KILOMETERS 

40 

-60

-60

-50

-100

-60

117o00' 116o00' 

34o

30' 

35o

00' 

Victorville 

Barstow 

Yucca

Valley

San Gabriel Mts

San Bernardino Mts

Little San Bernardino Mts

Sheep 

Creek 

Pipes 

Wash 

Morongo 

ground-water 

 basin 

Mojave River 

ground-water 

basin 

Lucerne

Valley

0 20 

KILOMETERS 

40 

Mojave River 

Deuterium (DD), in per mil, 

 dashed where uncertain 

EXPLANATION

Selected major faults 

Sampled well 

Less than -90 

-80 to -90 

-70 to -80 

-60 to -70 

Greater than -60

Tritium activity 

Dry lake 

Water containing tritium greater than 0.2 tritium units (TU) 

Carbon-14 activity, in percent 

 modern carbon (pmc). Dashed 

 where uncertain 

Less than 30 

30 to 50 

50 to 90 

Greater than 90 

Figure 22. Deuterium, tritium, and carbon-14 composition of water from wells in the western part of the Mojave Desert, southern 

California (modified from Izbicki, 2003, and Izbicki and Michel, 2003).

and carbon-14 activities are affected by chemical reactions 

between ground water and aquifer material. In general, 

ground-water ages estimated from carbon-14 activity that 

do not account for these reactions overestimate the groundwater age and may be much as 30 percent greater than estimated ages that account for chemical reactions between the 

ground water and aquifer material (Izbicki and others, 1995). 

Because of its longer half-life, carbon-14 data illustrate the 

cumulative effect of ground-water recharge over longer times 

than do tritium data. For example, ground water having a carbon-14 activity of 50 percent modern carbon was recharged 

5,730 years before present, and 30 percent modern carbon 

was recharged 9,950 years before present—assuming that 

there have been no chemical reactions between ground water 

and the alluvial deposits that compose the aquifer.

Carbon-14 activities near the mountain front are consistent with tritium data and show small amounts of ground-water 

recharge near Sheep Creek, Lucerne Valley, Pipes Wash, and 

Yucca Valley (fig. 22). Carbon-14 activities along the channel of Pipes Wash suggest that occasional flow in the wash is 

capable of supporting infiltration and subsequent ground-water 

recharge far into the Mojave Desert. Carbon-14 data also show 

recharge from intermittent streams near Cajon Pass, such as 

Oro Grande Wash (Izbicki and others, 1995), and show movement of water from the floodplain aquifer along the Mojave 

River into the surrounding regional aquifer. The data show 

that ground water in much of the study area has great age. In 

general, older ground water is found either at depth (Izbicki 

and Michel, 2004) or farther to the north—away from the front 

of the San Gabriel and San Bernardino Mountains.
182 Ground-Water Recharge From Small Intermittent Streams in the Western Mojave Desert, California

Summary and Conclusions

Small amounts of water infiltrate into the unsaturated 

zone underlying intermittent streams in the western Mojave 

Desert. In some areas, infiltrated water moves to depths 

below the root zone and ultimately to the underlying water 

table where it becomes ground-water recharge. The amount 

of water that ultimately infiltrates along a given reach is a 

function of streamflow availability (the quantity of water 

available to infiltrate into the streambed), the physical properties of the streambed, and geomorphic features that control 

the spatial and temporal distribution of infiltration of water 

infiltrated from stream channels. In some settings infiltration 

along a stream reach did not result in deep infiltration and 

subsequent ground-water recharge. Presumably, infiltrated 

water is transpired by vegetation along the stream. On the 

basis of this study, infiltration of about 0.7 m/yr represents 

a threshold below which deep infiltration and subsequent 

ground-water recharge do not occur—although this value is 

likely to differ in response to a number of factors including 

geomorphology, vegetation type and density, and the hydraulic properties of the underlying alluvium. In addition, it may 

take several hundred years for water to infiltrate through 

thick, heterogeneous unsaturated zones underlying some 

intermittent streams. This long time period dampens annual 

variations in recharge and variations in recharge from longerterm climatic cycles, such as El Niño or the Pacific Decadal 

Oscillation, toward a constant value. Given the time of travel 

and complex movement of water in thick, heterogeneous 

unsaturated zones, it may be unrealistic to assume that water 

infiltrated to depths below the root zone becomes groundwater recharge—especially where channel-abandonment 

processes on active alluvial fans may effectively strand water 

in the unsaturated zone before it reaches the water table. 

In contrast to the small amounts of ground-water 

recharge from numerous small streams that drain the San 

Gabriel, San Bernardino, and Little San Bernardino Mountains, the Mojave River is the largest single source of 

ground-water recharge in the western part of the Mojave 

Desert. Streamflow in the Mojave River recharges aquifers 

along the river throughout the study area to Afton Canyon more than 150 km from Cajon Pass and the mountain 

front. Cool moist air masses move inland from the Pacific 

Ocean and enter the Mojave Desert near the headwaters of 

the Mojave River near Cajon Pass generating precipitation, 

streamflow, and subsequent ground-water recharge. Similar 

processes also occur near San Gorgonio Pass in the southern 

part of the study area. These processes are different from 

recharge processes that occur elsewhere in the arid southwestern United States where streamflow, infiltration, and 

subsequent ground-water recharge are associated with precipitation and runoff in the higher altitudes of the mountains 

that surround the alluvial basins.

References Cited

Allison, C.B., and Hughes, M.W., 1978, The use of environmental chloride and tritium to estimate total recharge to an 

unconfined aquifer: Australian Journal of Soil Research, v. 

16, p. 181–195.

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