Map showing ground-water conditions in the Sacramento Valley area, Mohave County, Arizona; 1979

The Sacramento Valley area includes about 800² miles in northwestern Arizona and is bounded on the west by the Black and Buck Mountains and on the east by the Cerbat and Hualapai Mountains. The Black Mountains consist mainly of volcanic rocks; the Buck, Cerbat, and Hualapai Mountains consist of igneous, metamorphic, and volcanic rocks (Gillespie and Bentley, 1971, pl. 1). Sacramento Valley slopes gently southward and is underlain by alluvium and volcanic rocks to depths of more than 4,000 ft. Gillepsie and Bentley (1971, p. 1-15) divided the alluvium into three units - older, intermediate, and younger alluvium - and the volcanic rocks into two units - older and younger volcanic rocks.