DETACHMENT FAULTING ON THE EAST SIDE OF THE HUALAPAI MOUNTAINS, ARIZONA

On the eastern side of the Hualapai Mountains, Arizona is a previously reported but unmapped detachment fault trending northwest for more than 65 km. We refer to this detachment as the Blake Ranch Road Detachment (BRRD). Frost and Heideick (1996) first recognized the detachment from geophysical data. Mapping and drilling from 2007-2009 confirmed the detachment and its eastward dip. The footwall of the BRRD is made up of Precambrian igneous and metamorphic rocks and later Tertiary intrusives. The hanging wall is made up of at least two syntectonic, predominantly west dipping, sedimentary packages that rest unconformably(?) on Precambrian basement and/or Miocene volcanics. The syntectonic sedimentary packages consist of conglomerates with scattered siltstones and runout debris flows (sturzstroms). Movement on the BRRD appears to have started after the Peach Spring Tuff (18.5 Ma) was deposited and ended before or during the earliest deposition of the Big Sandy Formation (Pliocene).