Sherrod, D.R., Smith, D.B., Kleinkopf, M.D., and Gese, D.D., 1990, Mineral resources of the Kofa Unit 4 North Wilderness Study Area, Yuma County, Arizona, Chapter K, in Mineral resources of Wilderness Study Areas: Southwestern and south-central Arizona: U.S. Geological Survey Bulletin 1702-K, p. K1-K12.