ORIGIN OF DEBRIS FLOW DEPOSITS ON STARVATION CANYON FAN,DEATH VALLEY, CALIFORNIA

Three debris fan lobes with volumes of 8-25 million cubic yards were mapped on the Starvation Canyon alluvial fan in western Death Valley, California. These deposits were mapped atop the ~70 ka Qg2 alluvial fan indicating that the debris flows are younger. Starvation Canyon consists of Tertiary volcanic rocks at the mouth with faulted Cambrian and Precambrian metasedimentary rocks upstream to the west with the Granite at Hanaupah Canyon is 8.6 km upstream of the piedmont in the headwaters.

Field observations show that the northern lobe of the Qg2 deposits of the Starvation Canyon fan consist of grusified granite boulders at the surface. The debris flow deposits, which generally line a wash channel, are composed of 1-6 m diameter, varnished, but relatively unweathered, granite boulders with rare metasedimentarty boulders (<2%). The wash channel is incised through the Qg2 deposits with debris flow boulders overtopping the channel margins and resting atop the Qg2 deposits at the distal end. The southern lobe of the Starvation Canyon fan is composed of Qg3 gravels with an intervening active channel (Qg4). Both the younger and active channels are lined with large granite boulders (up to ~9 m diameter) that are unweathered and have very little, if any, varnish.

Based on the field observations, the conclusion that younger, unweathered granite boulders from debris flows are found atop the Qg2 gravel is correct. However, field observations are that the debris flow boulders are limited to the channel and channel margins. This infers that these deposits traveled along the incised channels and did not overtop the Qg2 gravels, aside from the area at the distal end of the fan. Thus, the flow volumes were of significantly lower volume than previously thought and, based on the dominance (>98%) and size (up to ~9 m) of granite boulders these flows would have traveled ~16 km before being deposited on the Starvation Canyon fan, with the origination point >8 km from the apex of the fan. The lack of continuity of these debris flows indicates emplacement by multiple events rather than one large event. This is based on the differences in weathering of the boulders as well as the disconnected nature of the debris flow deposits. The active channel (Qg4) is comprised of similar debris flow deposits as are found in the older channels.