Most of southern and western Arizona is covered with unconsolidated basin sediments that are not mapped in detail. Although these sediments have diverse physical characteristics, origins, and ages, they are generally mapped as generic units (e.g., Qal). This lack of detailed mapping is not unique to Arizona; it is estimated that 80% of the United States is still unmapped at intermediate or detailed scales (Molnia, 1992: 191). With recent developments in geologic dating techniques and improved understanding of weathering processes, there is now greater opportunity to distinguish and map unconsolidated sediments into genetic and temporal units. Recently, concerns in environmental geology have provided the impetus for surficial geologic mapping in Arizona (Demsey, 1989; Jackson, 1990; Field and Pearthree, 1991; Huckleberry, 1992a). These maps are of value to the scientific community because they provide insight into paleoenvironments and geomorphic history (Bull, 1991). More importantly, however, surficial geologic maps " ... can be applied to land-use management, assessment, and utilization, conservation of natural resources, groundwater management, and environmental protection. II (National Geological Mapping Act of 1992 (Section 2(b»). A recent example of the applied value of surficial geological mapping is the re-evaluation of flood hazards on alluvial fans (Pearthree, 1991). Surficial geology of the Middle Gila River Area, north-central Pinal County, Arizona, 5 map sheets, scale 1:24,000, with report.