Geologic map of the Wintersburg Area 7.5' Quadrangle and parts of the Arlington, Gillespie, and Tonopah Quadrangles, Maricopa County, Arizona v.2

The area covered by this geologic map includes all of the Wintersburg 7 ½' quadrangle and parts of the adjacent Arlington, Gillespie and Tonopah quadrangles surrounding the Palo Verde Nuclear Generating Station (PVNGS). The map area is located 40 to 55 miles (70-90 km) west of downtown Phoenix. The map area covers the piedmont between the Palo Verde Hills and the Hassayampa River and a 7 mile (11 km) reach of the Hassayampa River. The quadrangle includes the PVNGS, Interstate Highway 10, and numerous Maricopa County roads. It has experienced some suburban development associated with the PVNGS and is currently on the outer fringe of the greater Phoenix metropolitan area, so more development is likely in the future. The small bedrock hills in the southwestern quarter of the quadrangle were mapped by Charles Ferguson in the spring of 2005. Surficial deposits that cover most of the quadrangle were mapped by Philip Pearthree using color aerial photos from 1979, high-resolution digital color orthophotos provided by the Flood Control District of Maricopa County, National Agricultural Inventory Program (NAIP) photos from 2010 and 2013, and topographic information from U.S. Geological Survey maps and Google Earth. Field checking was done in the spring, summer and fall of 2005, with additional fieldwork in the fall of 2013 and the winter and spring of 2014. The mapping in 2005 was done in conjunction with geologic mapping of the Flatiron Mountain 7 ½' quadrangle (Spencer et al, 2005) to the north, and this quadrangle map is one of eight 1:24,000 scale geologic maps covering most of the Hassayampa Valley that have been produced in 2004 - 2006. This mapping was completed under the joint State-Federal STATEMAP program, as specified in the National Geologic Mapping Act of 1992. The additional mapping completed in 2014 was done in cooperation with Lettis Consultants International (LCI) as part of an investigation of seismic hazards for the PVNGS. Funding for this mapping was provided by Arizona Public Service.