The rocks and structures exposed in the Moon Mountains of the Colorado River Indian Reservation, west-central Arizona, record Mesozoic thrusting within the Maria fold and thrust belt, and superimposed Tertiary detachment faulting related to the regional Whipple-Buckskin-Rawhide detachment system. The major structures of the Moon Mountains are (1) the Valenzuela thrust fault, (2) the Moon Mountain detachment fault, and (3) the Copper Peak detachment fault. Lithologies consist primarily of Mesozoic and Tertiary intrusive rocks and crystalline gneisses of Precambrian age, with minor but important exposures of deformed and metamorphosed sedimentary and volcanic rocks. A newly-described section of metamorphosed, lower Mesozoic sedimentary rocks, the Valenzuela metasedimentary section, is assigned to the Buckskin Formation (Reynolds et al., 1987) of western Arizona.