Description:
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.