Geomorphic Evidence for Youngest Dated Faults in North-Central Arizona

Abstract

Faults that cut poorly consolidated debris* deposits on Sen Francisco Mountain, a Pleistocene composite wlcano in northern Arizona, form a complex, branching graben end a broad horst. The faults cen be no older then 0.46 Ma, the maximum age of the debris fan end be no younger than 0.25 Ma, the minimum age of a dach leva flow that cowred the fan's epex end blocked the drelnage of a sheem that dissected the floor ofthe graben. Topographic pmfiles reveal the fault scarps and demonstrate that the fan suhx has been offset by faulting. The displacements probably occumd during reedvation of older north-northeast- end north-northeast-trending structums in the rocks of the southern Colorado Plateau below the wkenlc deposits. The time of faulting is normally constrained in the late Pleistocene; it is the youngest dated faulting event in northcentral Arizona.