Description:
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)