Sediment yield and runoff frequency of small drainage basins 

in the Mojave Desert, California 

and Nevada

Peter G. Griffiths, Richard Hereford, and Robert H. Webb

Sediment Yield

One measure of geomorphic activity is sediment yield, which 

is defined as the amount of sediment per unit area removed from 

a watershed by flowing water during a specified period of time. 

Changes in sediment yield can signal changes in many elements 

of the desert ecosystem, including rates of weathering and erosion, climate, and human activity. Sediment yield affects rates 

of soil development and influences the recovery of disturbed 

surfaces downslope from source areas in desert landscapes. Sediment yield is strongly affected by surficial materials, topography, 

rainfall seasonality, and vegetation cover and can be increased 

by soil disturbance, which often occurs as the result of land use. 

Sediment yield from small arid basins, particularly in the Mojave 

Desert, is largely unknown owing to the ephemeral nature of 

desert streams and the long time intervals between flow events. 

Numerous railroads built in the early twentieth century to 

serve mining camps in the Mojave Desert provide a unique 

opportunity to measure recent rates of sediment yield. These 

railroads cross thousands of washes, but only the most prominent 

watersheds were given adequate drainage. In some cases, the 

railbed dammed small watersheds to create artificial reservoirs 

(Fig. 2). We identified numerous small reservoirs of this type 

(Fig. 3), where all sediment eroded from the upstream watershed 

has been trapped behind the railbed. Most of these railroads were 

built between 1906 and 1910, and sediment in them preserves 

nearly a century of sediment-yield history in the Mojave Desert.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3007

January 2006 Printed on recycled paper

The Mojave Desert

The Mojave Desert spreads across eastern California, southern 

Nevada, southwest Utah and northwest Arizona (Fig. 1). Since 

the 1950s, the population in and around the Mojave Desert has 

dramatically increased, and with it recreational, grazing, mining, 

military, and other activities. The federal agencies that serve as 

caretakers are often faced with difficult decisions as they work to 

ensure that the diverse and fragile ecosystem survives in the face 

of increasing land use. The first step in making sound management decisions is to understand the desert’s ecological systems, 

including the processes that shape the geomorphology, or surface 

features, of the desert landscape.

science for a changing world

USGS Recoverability and Vulnerability 

of Desert Ecosystems

Figure 1. The study area (Figure 3, outlined in green) is within the Mojave 

Desert (outlined in red), which covers 25,000 square miles. Elevation in 

the Mojave Desert ranges from below sea level in Death Valley to over 

1,600 m. Precipitation is between 65 and 190 mm annually, most of which 

falls during the winter season. 

Figure 2. Aerial view of the former Tonopah and Tidewater Railroad in 

Valjean Valley. Several small reservoirs appear as light-colored areas 

upslope (to the left) of the railroad bed. Photograph by M.P. Collier.

Arizona 

California 

Nevada 

Utah

250 km 

Las Vegas
as a recurrence interval (RI), the average number of years that occur between 

flood events. Runoff frequency is closely 

associated with the pattern of local precipitation, and changes in frequency can 

reflect changes in vegetation, land use, 

or climate. Runoff frequency can also be 

a major determinant of sediment yield. 

Runoff events were evaluated in 18 reservoirs by examining the stratigraphy and 

sedimentology of the deposits exposed in 

the walls of small pits (Fig. 4). In most of 

the reservoirs, individual flood deposits 

were distinguishable as couplets of sediment grading upward from silty-sand to 

silty-clay. Couplets as thin as 2 mm were 

identified (Fig. 5). The recurrence interval 

of sediment-depositing floods for each 

reservoir was calculated by dividing the 

lifespan of the reservoir by the number of 

distinct flood strata. The sediment record 

can be considered censored data in that 

it records only those streamflow floods 

of sufficient magnitude to deposit sediment in the reservoir. The smallest runoff 

events are not recorded.

Calculation of sediment yield requires 

measures of the area drained, the volume 

(or mass) of sediment removed, and the 

time interval over which deposition has 

occurred. Drainage area was calculated 

by integrating GPS coordinates collected 

along the boundary of each drainage 

basin. The volume of sediment captured 

in each reservoir was calculated by 

sampling the depth of the deposit with a 

soil augur at 1- to 2-meter intervals and 

integrating the results across the area of 

the reservoir. The time interval of deposi116°

37°

Death Valley

National Park

Nevada

Test Site

50 km

Burlington Northern

& Santa Fe RR

Carson &

Colorado RR

Barnwell &

Searchlight RR

Union

Pacific RR

Tonopah &

Tidewater RR

Las Vegas &

Tonopah RR Las Vegas

Ivanpah

Barstow Needles

Lone

Pine

Tecopa

Baker

Scotty’s Junction

Beatty

SP

BC

EM

SOM

SIL

TRR

Searchlight

118°

35°

California

Nevada Abandoned railroad

Active railroad

Town

Reservoir

Figure 3. Small reservoirs examined for sediment yield and runoff frequency history plotted along 

abandoned railroad beds.

Figure 4. The small reservoir at the Eagle Mountain (EM) site, along the Tonopah and Tidewater Railroad. The abandoned railbed is on the right.

tion was defined by the date of railway 

construction and either 1993, when some 

basins breached during regional flooding, or 2000-2001, when the stratigraphic 

analyses were performed. 

Runoff Frequency

Another useful measure of geomorphic activity is runoff frequency, defined 

as the number of streamflow events that 

occur in a watershed over a given time 

interval. This measure is often expressed 

137Cs Dating

In order to evaluate changes in flood 

frequency over the last century, the span 

of time represented by the reservoir 

deposits must be broken into shorter time 

intervals. This additional control on the 

age of deposits was obtained by sampling 

and analyzing reservoir strata for the 

presence of cesium-137 (137Cs) which 

is an anthropogenic isotope created as a 

by-product of nuclear fission. Introduction of 137Cs to the global environment as 

fallout began in 1952 when large amounts 

of 137Cs were injected into the stratosphere 

by the above-ground testing of high-yield 

nuclear weapons. Virtually all sediment 

exposed to fallout after 1952 contains 

detectable amounts of 137Cs, even if the 

sediment has been subsequently eroded, 
transported, and redeposited. 137Cs has 

been used extensively as a temporal 

marker in very young stream and lake 

deposits. Based on the absence or presence of 137Cs, individual reservoir strata 

were separated into pre- and post-1952 

periods, respectively, and flood frequency 

measures were calculated for each period 

(Fig. 6).

Runoff

Events

Basal gravel

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

cm

0

2

3

4

5

1

Surface

Coarse/fine

couplet

Bedding

plane

Figure 5. Stratigraphic section of reservoir deposits at the Silurian 3 (SIL) site showing runoff 

events represented by 16 coarse-fine couplets.

Figure 6. Stratigraphic cross section showing sedimentology and correlation of reservoir alluvium 

along a 284-km north-south transect. 137Cs is present in strata deposited after 1952. Cumulative 

number of runoff events is indicated to the left of each column.

0

5

10

15

cm

1952 horizon (137Cs presence)

1906 - 1908 horizon

?

SP

5

10

15

20

25

SOM

5

10

16

SIL1

5

10

19

TRR 1

5

10

15

20

30

35

BC

5

10

15

20

27

Results

Streamflow recurrence intervals were 

calculated for 14 reservoirs and ranged 

from 2.6 to 7.3 yrs with an average of 

4.7 yrs. Comparing pre-and post-1952 

deposits, the average RI increased from 

4.6 to 6.4 yrs, reflecting a decrease in the 

frequency of sediment-depositing floods 

in the second half of the 20th century. 

The decrease in runoff frequency may be 

related to concurrent changes observed 

by Hereford et al. (2004) in the regional 

precipitation regime: a shift from a wet 

period (1905 through 1941) to a dry 

period (1942 to 1978) known as the midcentury drought. This change was characterized by a reduction in the frequency 

of high-intensity precipitation (Fig. 7). 

Storm intensity is likely a good indicator of sediment deposition because of the 

censored nature of the preserved deposits. 

Although the frequency of storms and 

flow events may not have decreased, the 

reduced storm intensity probably reduced 

the frequency of higher magnitude floods, 

which are more likely to deposit sediment 

in the reservoirs.

Sediment yield at 15 reservoirs for the 

entire period of record averaged 28 metric 

tons km-2 yr-1, an order of magnitude 

smaller than sediment yields calculated 

for other regions (Fig. 8). This is not 

explained by variation in levels of precipitation; a similarly-sized, extremely arid 

watershed in the southern Negev Desert 

of Israel generates much more sediment 

(Fig. 8). The difference may be the result 

of storm types. Precipitation in the Negev 

is often generated by intense, localized thunderstorms, while most of the 

Mojave’s precipitation results from lowerintensity winter storms that are likely less 

erosive. Sediment yield from the Mojave 

basins may also be limited by the gentle 

gradient of the sampled watersheds, as 

well as the presence of coarse particles or 

desert pavements that protect most of the 

watershed surfaces and limit erosion.
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Days of high-intesity precipitation

0

1

2

3

4

5

6 Dry Episode

Figure 7. The average frequency of precipitation events on days of high-intensity precipitation 

shows a dry episode from 1942 to 1978. (High intensity is defined as precipitation > 90th percentile 

of all measurable daily precipitation at a station. Analysis is based on data from 52 weather stations.)

Figure 8. Graph showing the relation between sediment yield and drainage area for drainage 

basins in five different locations. Note that the Mojave Desert drainage basins generate an order 

of magnitude less sediment per unit area than basins elsewhere.

101

102

103

10-3 10-2 10-1 100 101 102 103 104 105

Southern

Arizona

Continental US 

Southwestern US 

Mojave Desert 

Negev Desert 

Drainage-basin area (km2)

Sediment yield (metric tons km-2 yr-1) In general, sediment yield from the 

Mojave basins decreased as drainage area 

increased, a trend typical of larger drainage basins in a variety of climatic and 

geologic settings (Fig. 8). Small drainage 

basins are usually topographically simple, 

and moving sediment the short distance 

required to exit the basin is a straightforward process. Sediment yield from small 

basins is typically supply-limited, meaning it is limited primarily by the supply 

of sediment, and sediment yield increases 

as a function of drainage basin area. 

As drainage basins increase in area and 

become more topographically complex, 

sediment yield often becomes transportlimited, meaning that sediment yield is 

restricted by the increasingly complex 

process of moving sediment out of the 

basin. For example, sediment eroded from 

steep headwaters can become trapped in 

flat bottomlands and increasingly complex drainage networks, which tend to 

grow more quickly than the headwaters 

as drainage area increases. Sediment trapping can also occur as water percolates 

out of the channel network and down into 

the basin substrate, a process known as 

transmission loss. Transmission losses 

will result in reduced streamflow and a 

decreased ability to transport sediment. 

The inverse relation between sediment 

yield and drainage area exhibited by the 

Mojave basins suggests that, like larger 

drainage basins elsewhere, these basins 

are transport-limited. Sediment-transport 

limitations such as channel storage and 

transmission losses may be enhanced by 

the low slope and coarse substrate of these 

particular alluvial fans. These limitations 

would also have a strong effect on the 

low-discharge, long-duration flood events 

generated from the low-intensity winter 

storms that characterize the Mojave Desert precipitation regime. 

Acknowledgements

This work was funded as part of the 

Recoverability and Vulnerability of 

Desert Ecosystems Project (RVDE) of 

the Priority Ecosystem Studies of the 

U.S. Geological Survey. RVDE is an 

inter-disciplinary partnership designed to 

develop a comprehensive understanding 

of the physical and biological processes 

that influence the desert’s vulnerability to 

disturbance and ability to recover. USGS 

scientists are creating maps, compiling 

existing scientific information, performing field and lab analyses, and are using 

the results to create decision-support tools 

designed to aid land managers.

For a full bibliography, see:

Griffiths, P.G., Hereford, R., and Webb, 

R.H., In press, Sediment yield and runoff 

frequency of small drainage basins in the 

Mojave Desert, U.S.A.: Geomorphology.

Hereford, R. Webb, R.H., and Longpré, C.I., 

2004, Precipitation history of the Mojave 

Desert region: U.S. Geological Survey Fact 

Sheet 117-03, 4 p.

For more information, contact: 

Peter Griffiths

U.S. Geological Survey

1675 W. Anklam Rd.

Tucson, AZ 85745

(520) 670-6671

Graphic design by Tina Kister