and U.S. Army
Earth Science Applications, National Training Center, Fort Irwin

Shaded relief maps constructed from Digital Elevation Models (DEMs)

California model from DEMs

[shaded relief map of California]

Shaded relief with color coding to show elevations

(Box shows Fort Irwin)

California model from DEMs

Shaded relief with color coding to show elevations (Box shows Fort Irwin)

Interpreting geography to learn about geology

In the northern two-thirds of the state, we can see an east-to-west succession of major features: the Sierra Nevada, the central valleys (Sacramento and San Joaquin Valleys), and coastal ranges. The Mojave Desert lies south of the Sierra as a relatively high-standing flatter area that forms a sharp wedge or arrow pointing west. It is rimmed by the Transverse Ranges on the south. North of the box representing Fort Irwin is the mountain-and-valley topography of Death Valley and nearby land; these mountains all trend north and the maps of this area were described by early geologists as looking "like an army of caterpillars marching north".

The distinctly different geographic provinces evident in this image are caused by distinctly different geologic origins. Some examples:

Death Valley area is segmented by north-striking faults that break the area up into long blocks, some of which subsided and others of which rose.
The Sierra Nevada is a huge uplifted block that was tilted as a result of miles of uplift along a fault on its east side, lifting that side up more than the west as if hinged at its west margin with the central valleys.
Major faults bound different geographic provinces, such as the sharp lines bounding the western Mojave Desert (the Garlock and San Andreas faults).

Depictions of geography such as these shaded relief maps are powerful tools for geologists and others who study the deserts and for those who apply this information to manage the deserts wisely.

DEM shaded relief models for the Mojave Desert

More state shaded relief models from DEMs. Click on the thumbnail or here to download gif files.

Black-and-white shaded relief map (78 kb gif) of the United States, by G.P. Thelin and R.J. Pike (Landforms of the Conterminous United States - A Digital Shaded-Relief Portrayal, U.S. Geological Survey Miscellaneous Investigations Series Map I-2206, 1991). Download the full dataset in tiff image format (11.8 MB)

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Fort Irwin from DEMs (click on image for 40k gif)

Geographic features

Light outline shows boundaries of the Army's National Testing Center

What is it?

This shaded relief image is constructed from gridded elevation data provided by USGS for 7.5-minute quadrangles. The data have about 30 m horizontal resolution. Several quadrangles are merged, and then the data are redrawn to show relief, which is shaded by a 'false sun' from a chosen direction.

Fort Irwin DEM model at higher resolution (about 290 kb)
Satellite image of about the same area.
DEMS on line

What can be learned from this image?

Several prominent mountains and alluvial basins show in the image, but roads and towns do not. Through much of the area, the mountains and basins are elongate east-west, a structural grain that is imparted by young faults and other deformation.

We can learn about geology; in particular lineaments and faults from this image.

Major faults, shown in red, form conspicuous lineaments on the image in many cases. These faults are active or were quite recently (past 15,000 years). Two main provinces can be defined based on the orientation of the faults (see illustration below). These provinces have very different landforms. The east-striking fault province has more relief from mountain top to basin bottom, and has broad alluviated basins. The northwest-striking fault province has less relief, forming a broad high area that generally lacks basins.

Provinces with differently oriented faults

We can learn about surface water drainage patterns. The Avawatz Mountains, in the northeastern corner of the image, are the highest in the area. Drainage prceeds from these mountains southward toward Bitter Spring. Other surface drainage also heads to Bitter Spring, including the Goldstone area. Some basins are isolated, however, and drain to dry lakes or playas. For instance, the Nelson Lake area and the area north of the Tiefort Mountains drain to Bicycle Lake at the west tip of the Tiefort Mountains.

Digital Elevation Models (DEMs)