Tertiary Extension and Fault-Block Rotation in the Transition Zone, Cedar Mountains Area, Arizona

New geologic mapping from the Cedar Mountains - Bloody Basin - Cooks Mesa area in the central Arizona Transition Zone presents an enigmatic geologic relationship that has previously gone unstudied. Here, fault blocks of Early Proterozoic basement overlain by Tertiary sedimentary and tuffaceous-lacustrine deposits and capped by a thick accumulation of basalt flows, dated in the project area between 15.1 and 13.5 Ma, are rotated ~20^o west to west-southwest along east-dipping normal faults.