Late Quaternary denudation, Death and Panamint Valleys, eastern California

Late Quaternary denudation rates are constrained from alluvial fans and tributary watersheds in central Death and Panamint Valleys. Preliminary results suggest that the denudation rate is in part a function of the mean watershed elevation. Rainfall increases semi-logarithmically with higher elevation to about 2500 m where it becomes limited by the regional average maximum moisture content of the air mass. The fan volumes show a power-law relation to the watershed areas. The fan volumes ranged from about 250,000 to 4000 km3 and the watershed areas range from about 60,000 to 2000 km2. The upper limit of the denudation rates estimated from small Death Valley fans restricted to the east side of the basin along the Black Mountain frontal scarp range between about 0.03 to 0.18 mm/yr. The maximum is made by assuming most of the clastic accumulation in these fans followed the last highstand of Lake Manly around 24,000 yr which is the least conservative condition. The upper limit of the denudation rates from the Panamint fans range from 0.04 to 0.20 mm/yr assuming the accumulation mainly postdates OIS-4 ∼60,000 yr or OIS-2 ∼20,000 yr based on the presence or absence of inset shorelines from the last glacial-pluvial maximum. The greater denudation rate associated with the higher mean watershed elevations can mainly be attributed to the greater rainfall at higher elevation. Denudation rates are about a third or less of the Neogene dip-slip rates reported from nearby active faults consistent with relief increasing during dryer periods.