Surficial geology of the Superstition Mountain Piedmont Area, northern Pinal and eastern Maricopa Counties, Arizona

One of the fastest growing areas of Arizona is the eastern part of the Phoenix Basin near the communities of Chandler, Gilbert, Mesa, and Apache Junction. Much of this development has occurred on the piedmont near the base of the mountains where little of the surficial geology has ever been mapped. Because this area of the Phoenix Basin will continue to grow in the future, there is a need to understand the nature and distribution of surficial deposits. Surficial geologic mapping provides a spatial data base for assessing potential geologic hazards (pearthree, 1991), for defining important groundwater recharge zones, and for analyzing the physical characteristics of surface deposits for excavation purposes. Such mapping is also valuable to earth scientists who are interested in defining the links between landscape evolution and climate change (Bull, 1991). This report presents the results of surficial geologic mapping in the eastern margins of the Phoenix Basin including the Superstition Mountain piedmont and Queen Creek alluvial fan (Figure 1). The region mapped is contained within the Florence Junction, Florence NE, Goldfield, Magma, and Superstition Mountains SW quadrangles (1:24,000), and part of the Weavers Needle quadrangle (1:24,000). This area contains a variety of landscape elements including steep mountain slopes, pediments, and alluvial fans. Included within this report is a discussion of the origins of pediments and an analysis of streamflow processes on the Queen Creek fan. (33 pages; 6 map sheets, map scale 1:24,000)