Remote sensing and mapping Miocene paleovalleys of the Marble, Bristol, and Old Dad Mountains in the Trilobite and Bristol Mountain Wildernesses, California

Abstract

Wilderness areas in the Mojave Desert, California, are remote and rugged terrain, but they contain important geology for understanding faults of the eastern California shear zone (ECSZ), and remote sensing offers techniques that can optimize mapping. The Bristol–Granite Mountain fault zone (BGMFZ) is the easternmost fault of the ECSZ with the Marble, Bristol, and Old Dad mountains on either side of the fault, as are the Trilobite and Bristol Mountain Wildernesses. In the northern Marble Mountains, a west-trending Miocene paleovalley has been proposed to have a correlative in the Old Dad Mountains and provides a constraint for right-lateral separation across the BGMFZ; however, this correlation is based on the premise that there was a unique paleovalley with a well defined geometry. In the northern Marble Mountains, a paleovalley was mapped by the distribution of (1) thickness and facies within the Lost Marble gravel (LMg) and 18.8 Ma Peach Spring Tuff (PST), and (2) adjacent highlands where the PST was deposited on basalt and dacite lava flows. Whether this paleovalley is unique, or there are other paleovalleys farther south in the Marble Mountains, requires mapping of the entire 5 by 28 km area of Miocene volcanic rocks. In the south Bristol and Old Dad mountains, there is a similar 12 by 22 km area of Miocene basalt and dacite with deposits of PST and local sedimentary rocks, including the proposed offset Lost Marble paleovalley, but the entire range needs to be mapped to establish a unique correlate. The mountains are in the Mojave Trails National Monument, and the Trilobite and Bristol Mountains wilderness areas, so access is limited. Remote sensing data, including aerial photography and hyperspectral images, are important for identification and characterization of rocks. Airborne hyperspectral Mako data can distinguish the distinctive spectral characteristics of the PST as well as several more map units identified by detailed field mapping in the Bristol Mountains. Reconnaissance maps derived from high spatial resolution Mako data can guide the detailed mapping needed to identify paleovalley or paleohighland deposits and can be used to optimize field time.