Surficial Geology of the Eastern Gila River Indian Community Area, Western Pinal County, Arizona

Geologic maps have traditionally emphasized bedrock rather than unconsolidated sediments, the latter usually being lumped into the generic category of "Tertiary and/or Quaternary alluvium". This tradition has left many areas, especially those within the Basin and Range physiographic province, incompletely mapped. Recently, however, there have been systematic efforts to map unconsolidated surficial deposits at small (1:500,000), intermediate (1:100,000), and large (1:24,000) scales (Demsey, 1989; Field and Pearthree, 1992; Hunt, 1978; Jackson, 1990). The impetus for surficial geologic mapping lies in the fact that humans have a vested interest in knowing the distribution and nature of late Cenozoic geological deposits and landforms. Most of the Southwest's urban areas including Albuquerque, El Paso, Las Vegas, Phoenix, and Tucson lie on basin fill. Consequently, there is an interest in the physical properties of the substrata, the distribution of industrial minerals, and the potential for flooding and other geologic hazards. These types of information can be obtained from surficial geologic mapping (Pearthree, 1991). In addition to engineering concerns, other research-oriented information can be gained as well. Because surficial geologic mapping is based on temporally discrete geomorphic surfaces, it provides insight into climatic and tectonic mechanisms of landscape evolution (Bull, 1991). Also, surficial geologic maps can be used to assess subsurface archaeological potential (Davidson, 1985) and serve as a guide for avoiding archaeologically sensitive areas.