Surficial geology of the Wittmann and Hieroglyphic Mountains Southwest 7.5' Quadrangles, northern Maricopa County, Arizona

Most of southern and western Arizona lie within the Basin and Range physiographic province, a region characterized by broad valleys and linear mountain ranges. The valleys are deeply filled with alluvium that has eroded from adjacent mountains during the last 10 My 1. This aggradation has been driven by tectonism and climate change, although regional tectonic stability within the last 5 My suggests that climate change is the more recent dominant driving force (Morrison, 1985). Climatic fluctuations between relatively wet and dry conditions have resulted in pulses of aggradation producing a mosaic of different aged alluvial deposits in piedmont areas. Urban development on piedmonts, especially in the Phoenix Basin, has created a need to better understand the distribution and nature of these deposits. Surficial geologic maps characterize and distinguish different piedmont deposits on the basis of age and genesis. Such information provides baseline data for evaluating geologic hazards potential (e.g., Pearthree, 1991), locating possible source areas for industrial minerals (e.g., Wellendorf et aI., 1986), and determining locations favorable for groundwater recharge (e.g., Huckleberry, 1994). Moreover, these maps are also useful for assessing the potential for buried cultural resources and providing insight into local geologic history and landscape evolution. This report presents the results of surficial geologic mapping in the Wittmann and Hieroglyphic Mountains SW 7.5' quadrangles located northwest of metropolitan Phoenix (Figure 1). The project area includes segments of U.S. Highway 60, State Route 79, and the Central Arizona Project Canal, and is contiguous to the south with the White Tanks Mountain piedmont area previously mapped by Field and Pearthree (1991). (24 pages; 2 map sheets, map scale 1:24,000)