The study area is situated along the southern edge of the Superstition Mountains approximately 40 miles east of the greater Phoenix metropolitan area (Figure 1). Geology is dominated by mid-Tertiary volcanic rocks of the Superior volcanic field (Ransome, 1903), and these rocks depostionally overlie a crystalline basement of early Proterozoic Pinal Schist intruded by middle Proterozoic granitoids. In some areas a relatively thin sequence of the Middle Proterozoic Apache Group occurs along the contact between these two rock types. The volcanic stratigraphy of the southern Superstition Mountains changes abruptly from a sequence dominated by lavas on the south, in the Whitlow Canyon Area, to a sequence dominated by the thick Superstition tuff to the north. The transition corresponds to the southern edge of a large volcano-tectonic depression referred to as the Superstition Cauldron (Sheridan and others, 1970; Sheridan, 1978). The Superstition Cauldron is bounded to the south by a broad valley underlain by Proterozoic basement. This valley is thought to represent the upturned, highly fractured, and therefore recessive, margin of the Cauldron. The valley serves as the main barrier to correlation of the Tertiary volcanic stratigraphy in the study area. The most important structural feature of the study area is a major west-side-down normal fault that runs along the east edge of the map area. The fault, referred to as the Elephant Butte fault is probably continuous with the concealed and inferred, western range-bounding fault of the southeasterly adjacent Mineral Mountain Area. The Elephant Butte fault appears to have had a great influence on the Tertiary stratigraphy and volcanic structure of both physiographic regions. ( 24 pages)