Faulting and Fssures in the Higley Basin, Central Arizona

The Higley Basin, located in central Arizona, contains several faulted buried bedrock highs and is composed of nearly 12,000 feet of alluvial fill that is largely heterogeneous, with vertical and horizontal facies changes throughout.   Differential compaction of heterogeneous alluvial fill along faulted bedrock highs due to ground water pumping has resulted in a drop of approximately 200 to 300 feet in ground water levels.   Approximately 5 feet of subsidence has occurred in the Higley Basin, along with earth fissuring since the 1950’s when the effects of ground water pumping were first noted.  In our basin analysis of the Higley Basin, we have used multiple investigative techniques, such as detailed lithologic analysis of hundreds of borehole logs, gravity surveying and depth-to-bedrock modeling, with InSAR imagery and detailed earth fissure mapping to elucidate the geologic framework in which earth fissures have evolved.  Multiple earth fissures have evolved around a buried bedrock high, often referred to as Hawk Rock, and continue to grow after high-intensity rainfall in the summer months.  The Hawk Rock area contains several normal faults and fine-grained deposits adjacent to coarser-grained sands and gravels. InSAR imagery shows abrupt truncations of subsidence features that trend to the northwest. We have interpreted these truncations as sharp changes from shallow buried pediment to a deepening of the basin due to faulting.  The trends of our newly interpreted faults from lithologic mismatches, InSAR imagery and steep depth to bedrock contours are consistent with other faults in Higley Basin identified by previous workers and may become the future sites of earth fissuring with continued ground water withdrawal.