Philip A. Pearthree

This report presents an assessment of the seismic hazard associated with the Sugarloaf fault, which crosses State Route (SR) 87 near Mesquite Wash in central Arizona. The Sugarloaf fault is a 20 km (12 mile) long, northwest- to north-trending normal fault with displacement down to the east. We conducted a multi-faceted investigation in order to evaluate the late Quaternary behavior of the Sugarloaf fault and assess the seismic hazard associated with it.

This report presents the results of a reconnaissance analysis of Quaternary faulting in central Arizona, conducted for the U.S. Bureau of Reclamation. The goal of this study has been to thoroughly delineate locations of possible Quaternary faulting in the area surrounding existing and potential dam sites in central Arizona.

This report is a compilation of available data on Quaternary faults in Arizona as of the summer of 1998. These data were compiled as part of a effort to compile data and map information on Quaternary faults throughout the world, which is being overseen by Michael Machette of the U.S. Geological Survey.

A distinctive suite of volcanic, sedimentary, structural, and physiographic characteristics permits differentiation of the post-1 2- to 15- Ma Basin-Range disturbance from earlier mid-Tertiary extensional tectonism in Arizona. Basin-Range volcanism comprises basalts or bimodal basalt-rhyolite suites that are concentrated in several fields in central and northern Arizona; the age of volcanism generally decreases northeast and east onto the Colorado Plateau margin.

This map presents data and interpretations concerning the distribution, amounts and timing of neotectonic faulting in Arizona. It is one part of a larger study and analysis of the neotectonic framework of Arizona..

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Susan Blake

Apache Leap Special Management Area
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