A large region of the west from southeastern Oregon and part of Idaho, through nearly all of Nevada, western Utah into most of southern Arizona and eastern California is known as the Basin and Range province. This province, dominated by uplifted blocks of sedimentary and igneous-metamorphic rocks set between broad, flat valleys swings eastward through New Mexico into West Texas, and continues southward into Mexico. Typical examples of the varied landscapes are shown on this page.

### The Nevada Basin and Range; The Desert Southwest; and The Snake River Plains

The Colorado Plateau ends in western Utah. Almost the entire state of Nevada falls within the Basin and Range province. This Landsat image mosaic shows much of that province in most of Nevada but Death Valley, the southern Sierra Nevada block, and a bit of the Great Valley (San Joaquin) near Bakersfield, are in California.

Major C.E. Dutton, an early explorer of the American West, described these mountains as they appeared on a map as resembling "an army of caterpillars crawling northward out of Mexico". That is re-enforced by the next image, a shaded topographic depiction of the region made from DEM data (method described on page 11-5; another example is on page 7-2). This rendition emphasizes the notable flatness of the valley floors in the basins.

The ranges can be quite distinctive, standing out between valleys as bare rock, since many are almost devoid of arboreal vegetation. This scene is in Nevada:

Another range occurs north of Tucson, AZ and is capped by a pine forest. At the foot of the Santa Catalina Mountains, shown below, is a thick, deeply gullied alluvial fan.

Such characteristic topography results from a complex structural history dominated by block faulting (somewhat like the faulting we described in Kenya on page 3-2). The region, as it underwent tensional stresses during uplift of the crust, responded by fracturing. The fractures trend mostly north-south, along which segments dropped down (faulted), leaving adjacent range blocks higher. The present elevations can be greater than 2,700 m (8,900 ft), producing relief of 900 to 1,520 m (3000 to 5000 ft) relative to the basins. Among the major ranges in this scene are the Shoshone, Toyabe, Toquima, Monitor, and Hot Creek Mountains; higher slopes are forested, as suggested by the reds in this September scene.

The intermontane basins between ranges are back-filled with great amounts of rock debris descending downslope, so that the valley floors move upwards as the ranges wear down. The central (lowest) surfaces of some of the basins contain playas (deposits of fine sediment left after intermittent lakes evaporate following the rainy season) that are light-toned in the image. Between playas and ranges, along the transitional zone known as a piedmont (literally, "foot of the mountain"), are deposits of coarser sediment (up to cobbles and boulders in size), mixed with clays that make up alluvial fans (dark gray in the image).

One of the classic areas within the Basin and Range, near its southwest margin, contains Death Valley and other block fault ranges. We show it below (locate it within the above mosaic) along with a map indicating the names of the principal topographic features.

Below the Death Valley area, the Basin and Range ends against the Mojave Desert. That region is located within the structural salient north of the southern California Transverse Ranges (see page 7-2).. Small ranges within the Mojave closely resemble the barren block fault mountains of the Basin and Range types. Here is a color radar image of an area near Barstow, California, made from SIR-C C- and X-band imagery (see page 8-7). Note the alluvial fan (in blue).

The Basin and Range type of geology is widespread over western North America. From Oregon-Idaho through Nevada and Utah, it spreads east into southern Arizona and New Mexico into northern Mexico itself. One area of classic ranges and valleys is around Phoenix, with Las Vegas the fastest growing cities in the southwest U.S. The next image was an experiment done in the early days of Landsat-1 to use MSS Band 7 (IR) to render vegetation green. The fertile (irrigated from reservoir lakes) land in the Salt River Valley within which Phoenix was built shows up as actively growing in this February, 1973 image:

Around and south of Phoenix the mountain ranges are small and isolated. North are the high, forested Mazatzal Mountains - a much larger block that includes also the Sierra Ancha and Pinal Mts. In the latter, note a pinkish red patch, which marks mine waste from the Globe-Miami-Superior copper mining district. In these mountains is the dammed Roosevelt Lake: it is a wonder on weekends to find 1000s of power boats being hauled from Phoenix to cruise those waters.

By now, you have gained experience with picking out features in the landscape at the medium scales presented in Landsat imagery. Before finishing our trip, we challenge you to apply your experience by locating or identifying geographic and geologic landmarks in a space image somewhat to the south of our main flight line. This image is much smaller in scale, covering about 1,100 km (684 miles) on a side. Make this a game of finding the places listed below. Look over the black and white Day-Vis HCMM image that shows most of the southwestern U.S. (part of southern California and Nevada, most of Arizona, a bit of Utah, and small segments of the Mexican states of Baja California and Sonora), including some of the Basin and Range.

6-11: Use a U.S or World Atlas to aid in correlating landmarks in the scene with mapped features. To help you get oriented, the red numbers 1, 2, and 3 are the Salton Sea, Lake Mead, and Lake Powell, respectively. Pin these down on an atlas to give you a feel for the scale. Then, relying on the maps, identify what is at or around the numbers 4 through 10. (The answers are below). Finally, without the aid of number guides, try to find the Gulf of California, San Diego, the Imperial Valley, the Sierra Nevada range, Las Vegas, Phoenix, and Tucson. Also, what is the name of the great geologic fault that marks (as a straight tonal boundary) the southern edge of the Mojave Valley? ANSWER

The northern end of the Basin and Range abuts against the Snake River Plains in Idaho, seen here in this Landsat-1 full scene:

The Idaho Rocky Mountains are seen near the top. The Plains themselves are a series of bluish-gray lava flows (mostly basalt) that began some 10 million years ago. More recent is the large Crater of the Moon National Monument - the conspicuous black blotch. Water from the Snake River is used to irrigate the farms that produce Idaho potatoes, sugar beets, barley, wheat.

In 1963, when the writer (NMS) was working in the AEC's Plowshare program (at Livermore, CA) for engineering uses of nuclear explosives, he was given the responsibility of finding a site in the plains basalts for Project Schooner. The most promising area was Bruneau Canyon just west of the left edge of this image. After more than a month on site, and several expensive drill holes, he recommended abandoning this once promising area (the county where the detonation would have taken place has 25000 cows and less than 5000 people - logistically favorable) when unexpected lake beds were found buried by younger flows near the surface.

Primary Author: Nicholas M. Short, Sr. email: nmshort@ptd.net