inngeo

CALIFORNIA


Text excerpt from log report for Day 7:

Pediments can be found in many parts of the globe, their occurrence is not dependent on any particular climate. In areas of scarce vegetation and moderate erosion depths, pediments can best be viewed and studied in arid and semi-arid regions. As a result, most related research has been conducted in such areas (Ahnert 1996, 280). In geo-morphologic terms, a pediment is a gently inclined slope created through erosive processes of denudation; a clearly discernible fold - the so-called "pediment fold" - sets this slope visible off against a much steeper back slope. The border between this pediment and the back slope is marked by the difference in their degree of slant. While the back slope's tilt is more than 20 degrees, the inclination of the pediment area is not more than between 7 - 11 degrees toward the succeeding plain.

Picture: Pediments, alluvial fans and playas in Death Valley
Picture: "Devil's Golf Course" in Death Valley
Picture: "Devils Cornfield" in Death Valley

In the southwestern U.S., pediments have formed between tectonically lifted crust blocks on the one hand and the sunken and sedimented areas of the "playas" on the other. Their formation depends in part on the erosive force of water, even though precipitation in this area is very scarce. The creeks running from the mountains into the basins (playas) generate lateral erosion as they "nag" off the spurs at the valley exits. Amidst the pedimentary areas that remain in the bedrock covered only by a thin sedimentary layer, one may occasionally find particularly hard (resistant) rock, forming so-called "inselbergs." The loose material is deposited where the pediment changes into the basin area, forming a "bajada;" it may also lead to sedimentation of the "playas" (cf. fig. 10/2). From a topographical point of view there is a characteristic succession of mountain edge - pediment - bajada (glacis) - playa (Ahnert 1996, 280).


<< Back