QUATERNARY GEOLOGY OF THE JUNE LAKE DISTRICT, CALIFORNIA

Abstract

In the June Lake district of east-central California, the Sierra Nevada has been uplifted along a number of closely-spaced faults, and the rectilinear outline of the range front is controlled by their pattern. That repeated movement is characteristic of these faults is shown by increasing throw where they cut successively older moraines. There were at least four ice advances in the Pleistocene: the earliest stage, here named the Aeolian Buttes, was followed by the Sherwin, Tahoe, and Tioga, previously named by Blackwelder. Constructional forms have been destroyed on the two older tills but are preserved on the later ones. Large quantities of rhyolitic ash and pumice, now the welded Bishop tuff, were erupted in the interval between the Aeolian Buttes and Sherwin glacial stages. A small basalt flow near June Lake rests on Tahoe till and was glaciated in part by Tioga ice. Plug domes and flows of rhyolitic obsidian of the Mono and Inyo craters were erupted following the Tioga stage. Pumice from these volcanoes covers late recessional moraines, and these volcanic slopes near Mono Lake are not cut by Pleistocene shore lines. Mono Lake was much larger in the Pleistocene, and the name Lake Russell is proposed for this lake. During the Tahoe stage the lake had an outlet to the southeast and was connected with the Owens Valley-Death Valley system of lakes and channels.