LAKE MANLY DEPOSITS AT THREE BARE HILLS, PARK SERVICE RIDGE, NPS 5/190 JUNCTION, AND MUD CANYON JUNCTION, DEATH VALLEY, CALIFORNIA

The precise age and depth of pluvial Lake Manly (LM) is a continual enigma. Debate over the age of the high elevation lake deposits wavers between 186-127 ka and 20-12 ka in Marine Isotope Stage (MIS) 6 or MIS 2, respectively. Luminescence and cosmogenic nuclide dates of the high elevation lake shoreline deposits are within MIS 6. Determining the true depth of LM is confounded by tectonics. On the Black Mountains along the uplifting east side of Death Valley prominent lake deposits are found at 90 m above sea level (masl) with higher shoreline features (at 125 masl) found on the Pleistocene basalt of uplifting Shoreline Butte in southern Death Valley. On the tectonically less active west side of Death Valley, 130 ka cosmogenic nuclide dated LM deposits are found at 30 masl and an undated lake gravel bar at 61 masl. In this study, we mapped purported LM deposits at Three Bare Hills (TBH), Park Village Ridge (PVR), NPS 5/190 junction (5/190), and the NPS 5/Mud Canyon Road junction (MCJ) where the LM deposits are relatively unaffected by vertical uplift near the strike-slip Northern Death Valley fault.

At TBH, LM gravels were mapped up to 72 masl with a prominent wave-cut riser at 53 masl. We infer that a 0.8-km-long N-S trending spit formed by north to south longshore drift. We interpret the northwest trend at the south end as the result of west to east-trending waves. At PVR, LM deposits found as high as 72 masl unconformably overlie the Funeral Formation. Horizontal features consistent with wave-cut shorelines were found at various lower elevations. East-dipping foreset beds were formed by west to east-trending waves. At 5/190, LM deposits are the remnant of a northeast-southwest trending spit that is found from 30-20 masl, and are overlain by Qg3 (30-7 ka) alluvial fan deposits. At MCJ, LM deposits form a low, nearly east-west trending ridge at 43 m overlain by Qg2 (70 ka) alluvial fan deposits.

The 72 masl LM deposits at TBH and PVR are relatively unaffected by tectonic uplift compared those at 90 masl on Black Mountains. If this interpretation is correct, then 72 masl is likely closer to the true elevation of the LM shoreline at MIS 6. A 72 masl shoreline translates into an estimated maximum lake depth of ~147 m. The wave-cut features and deposits from 53-31 masl suggest that the LM recession was relatively slow through this interval.