The geology of a portion of Humphreys and San Fransisquito Quadrangles

Abstract

The rocks of this area range in age from the pre-Cambrian Pelona schist to the Recent alluvium. This metamorphic formation is separated from the two sedimentary formations by a formation of two igneous intrusives, which have been faulted into their position between the Pelona schist and the Sespe (Oligocene?) formation, the igneous rock, granodiorite and leucomonzonite, caused the extreme tilting of the Sespe when they were faulted into their present position. These rocks are probably of Jura-Cretaceous age. The Sespe is a thick series (approx. 4000 ft.) of continental deposits, now in a more or less consolidated condition. The Lower Upper Miocene Mint Canyon formation is another continental: series deposited unconformably upon the Sespe. It consists, in the lower section, of coarse conglomerates, sandstones and shales with some ash beds in the upper part which show some volcanic activity during Upper Miocene times. The region then underwent some folding and gentle tilting in post- Miocene times and a mature land surface was formed. There was a deposition of terrace material in probably Pleistocene time after which the region suffered continuous uplifting until the present time.