GEOLOGY OF A TERTIARY INTERMONTANE BASIN OF THE LAST CHANCE RANGE, NW DEATH VALLEY NATIONAL PARK, CALIFORNIA

A hypothesized Pliocene fluvial connection between Owens Valley and Death Valley that predates the course of the Pleistocene Owens River would provide a migration pathway for aquatic and other species. The mapped Tertiary sediments and basalt flows hold one key to developing an accurate model of the paleo-river during this time. Previous mapping of the Tertiary sediments and flows was limited to spatial distribution with limited description of the deposits themselves.

In the central Last Chance Range is ~4 km² of Tertiary sediments and basalt flows. The Tertiary deposits are along a N-S trending canyon that is underlain primarily by tilted Cambrian-age carbonates of the Bonanza King and Nopah Formations. To better understand the source and nature of these rocks, I constructed a ~1:12,000 geologic map, described the sediments and collected two basalt samples. The basalt was powdered and analyzed by X-Ray fluorescence to determine its geochemical composition.

In the north, the base of the Tertiary sediments consists of course, well-cemented, landslide debris consisting of Bonanza King and Nopah clasts. In the south, the basal unit is debris flow deposits of quartzite boulders. Overlying these coarse deposits are yellow, tan and gray sandstone and breccia with a basalt flow near the top of the section. The Tertiary deposits are capped by a second basalt flow. The beds are folded into a N-S trending syncline. The composition of the basalt is similar to basalts found 3 km to the north in the Last Chance Range.

The quartzite debris flows are enigmatic. Clast imbrications within the debris flows indicate NW-SE flow. The closest outcrop of quartzite to the NW is the Cambrian Zabriskie Quartzite (>2 km) and outside the present drainage basin. No outcrops of quartzite are mapped to the north, east or south. The correlation of basalt flows between basins in the Last Chance Range combined with the exotic quartzite clasts suggest that these now isolated deposits were once part of a larger intermontane basin that extended to the N and NW. The N-S trending fold suggests E-W-oriented compressive stresses post-Pliocene.

The advisor for this project was Dr. Jeffrey Knott (CSUF). Dr. Jade-Star Lackey (Pomona College) provided XRF facilities. Financial support provided by a grant from CSUF Associated Students, Inc. and a CSUF Incentive Grant (to Knott).