Late Cenozoic evolution of the upper Amargosa River drainage system, southwestern Great Basin, Nevada and California
A major part of the upper Amargosa River drainage system is centered on Timber Mountain, a high central area within a volcanic caldera northeast of Beatty, Nevada, on the west margin of the Nevada Test Site. The basic drainage pattern in this area was established soon after caldera collapse and resurgent dome formation about 11 million years ago. The gross drainage pattern has changed little since then, although subsequent volcanic activity has temporarily blocked drainage channels. As there have been no significant changes in subbasin geometry, general tectonic stability of the region during this time is implied. A major change in alluvial regimen occurred with the end of major alluvial-fan construction within the drainage system and the beginning of fanhead erosion that formed incised washes. The size and shape of incised channels differ, but they show a similar relation to the geomorphic parameters of their respective drainage basins---including such diverse-appearing washes as the deep Fortymile Wash and the wide, shallow wash on the Amargosa River downstream from Beatty. If the subbasin drainages have not changed appreciably during the Quaternary, then the forcing mechanism for the change in alluvial regimen is most likely either climatic or tectonic. Because this change appears to have occurred at about the same time throughout the upper Amargosa River drainage system, a climatic cause is preferred; its nature and timing are still speculative, but probably was increasing aridity that reached a threshold in the middle Pleistocene. This analysis also concludes that a postulated Pleistocene drainage capture by the Fortymile Canyon drainage system did not occur and that a large Pliocene lake in the Amargosa Desert, the postulated ``Lake Amargosa``, is equivocal.
- Research Organization:
- Geological Survey, Menlo Park, CA (United States)
- DOE Contract Number:
- AI08-78ET44802
- OSTI ID:
- 60454
- Report Number(s):
- USGS-OFR-87-617; ON: DE88010306
- Resource Relation:
- Other Information: PBD: 1988
- Country of Publication:
- United States
- Language:
- English
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