Geologic map and geochemical data for the Bradshaw Mountains in the Mayer-Crown King area of Yavapai County, Arizona. Map scale 1:24,000

The accompanying geologic maps depict the general geology of a two-mile wide strip centered about the Salt River, starting just below Roosevelt Dam and extending westward 36 miles to just below Granite Reef Dam. The geology was accomplished from October 1980 through April 1981, with the aid of about 25 hours of helicopter logistical support time. Discussions and/or field assistance by Mike Pryor, Joe Bailey, Dick Raymond, Paul Damon, and Tom McGarvin are greatly appreciated. Geologic Summary The lower Salt River below Roosevelt Dam has cut a gorge which exposes much of the geology of the northern Superstition volcanic field. The silicic field of late Oligocene (?) and Miocene age is one of the half dozen or so found in southern and western Arizona. The volcanics extend continuously from around Apache Lake Resort westward to Stewart Mountain Dam, and discontinuously farther west to the Mt. McDowell area, around Granite Reef Dam. The Superstition volcanics were deposited on Precambrian crystalline rocks, dominated by a biotite quartz monzonite which age dates at about 1400 m.y., and which is probably equivalent to the Ruin and Oracle granites further east and south. The northern Superstition volcanics are dominated by silicic pryoclastics, plugs, ash flows, agglomerates, and late stage intrusive domes. Rocks of andesitic composition are subordinate in volume although important in the eastern part of the area.

This map depicts the geology of the Lewis Springs 7 ½' Quadrangle, which is located in the upper San Pedro Valley a few miles north of the U.S. – Mexico border. The quadrangle covers much of the piedmont west of the San Pedro River and south of the Babocomari River, including the eastern fringe of Sierra Vista and a portion of the Fort Huachuca Military Reservation. The quadrangle also covers about 10 miles of the San Pedro Riparian National Conservation Area along the river, and bedrock hills and a small portion of the piedmont east of the San Pedro River. The geology of the quadrangle is diverse and includes Cretaceous sedimentary and igneous rocks, extensive exposures of the upper part of the late Cenozoic basin-filling deposits, and Quaternary surficial alluvium deposited by tributary streams and the San Pedro River. This map is one of 7 1:24,000-scale geologic maps that have been completed recently in the upper San Pedro Valley. Other maps cover the Fairbank (Ferguson et al, 2006), Land (Shipman and Ferguson, 2005), St. David (Youberg, 2005), Huachuca City (Pearthree, 2003), McGrew Spring (Shipman and Ferguson, 2003), and Benson (Youberg et al, 2004) quadrangles. This mapping was completed under the joint State-Federal STATEMAP program, as specified in the National Geologic Mapping Act of 1992. Revisions to this map were made in 2008 and 2009 as part of an effort to systematically map Holocene alluvium associated with the San Pedro River; funding for this effort was provided by the Arizona Department of Water Resources.

The Fairbank map area is dominated by an Upper Cretaceous plutonic-volcanic complex that is closely associated with silver-rich, porphyry ore deposits of the Tombstone district (Goodale, 1927; Butler et al., 1938; Newell, 1974; Devere, 1978; Williams, 1980) located directly east of the map area. The volcanic rocks overlie Lower Cretaceous siliciclastic strata of the Bisbee Group with angular unconformity. The older rocks were folded into northwest-striking folds that show evidence for two phases of deformation. The Upper Cretaceous volcanics are moderately to gently tilted to the northwest forming two low-lying, southwest-striking horst blocks. A fairly major southeast-side-down normal fault, of probable middle Cenozoic age, is interpreted to cross the San Pedro valley diagonally from northeast to southwest just to the southeast of the northwestern horst block. A panel of volcaniclastic conglomerate of probable middle Cenozoic age is barely preserved overlying the volcanics along the northwestern flank of the northwestern horst block just to the north of this map area (Shipman and Ferguson, 2005). A small outcrop of similar conglomerate is tentatively identified overlapping the southeastern horst block. Another strip of conglomerate occurs parallel to and along the crest of the northwestern horst block, but this conglomerate dips steeply to the southeast and is bounded by a gently northwest-dipping normal fault. The age relationship between the two oppositely dipping conglomerate sequences and faults is unknown.

The Daggs Tank 7.5-minute Quadrangle is located approximately 40 miles (60 km) northwest of downtown Phoenix on the east side of Hassayampa Plain. Much of the map area consists of the western piedmont of the White Tank Mountains, but the western third of the map area is dominated by deposits of the south-flowing Hassayampa River, a major regional drainage in central Arizona. The surficial geology depicted in this map is modified from Field and Pearthree (1991b), and includes new field mapping and aerial photograph interpretation using high-resolution digital images provided by Maricopa County. Tertiary volcanic rocks were mapped for this study, but much of the rest of the bedrock was mapped by Barret (1976) and modified locally based on new field mapping, and on mapping and examination of rock units in the adjacent Wagner Wash Well 7.5-minute Quadrangle (Ferguson et al., 2004).

The Wagner Wash Well 7.5-minute Quadrangle includes the western fringe of the central White Tank Mountains, the western piedmont of the White Tank Mountains, the south-flowing Hassayampa River, and a small part of the piedmont west of the Hassayampa River. Purpose: The intention of this investigation is a multiyear mapping program directed at producing geologic map coverage for the Hassayampa River corridor and greater Phoenix metropolitan area. The primary product resulting from new mapping in the study area is a 1:24000-scale geologic map describing rock units and other geologic features. Revised and re-released with funding from the USGS National Geological and Geophysical Data Preservation Program, award no. G17AP00114. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.

The Tank Mountains of southwestern Arizona are a west-northwest trending range which represent an approximately 30 km-Iong extension of a southeastern arm of the Kofa Mountains. On all other sides, the Tank Mountains are surrounded by gently southeastsloping Quaternary peidmonts of the Gila River drainage basin; Palomas Plain on the north, east, and south and King Valley on the southwest. Elevations in the Tank Mountains are between 2,200' and 900', and in general elevation decreases to the southeast. The Tank Mountains lie within the Sonoran biozone, and although there are no active springs, washes within the range that cut into bedrock are renowned for deep potholes or "tanks" which hold water for long periods of time. The mountain range derives its name from these features, the most prominent of which is White Tanks in the north-central part of the range. Originally, the western Tank Mountains were known as the Frenchman Mountains, and the southeastern part of the range were called the Puzzles Mountains (Wilson, 1933). There are only five formally recognized place names in the map area according to the 7.5' USGS quadrangles (Palomas Mts. NW, NE, SW, SE). Two other informal place names are used in this report and they are identified on Figure 1. The informal name Malley mesa is derived from a triangulation station at the crest of the prominent mesa at the northeast terminus of the Tank Mountains. Dummy gulch is a major southeast flowing wash in the eastern Tank Mountains named by local inhabitants for a dog named "Dummy" who was lost there chasing deer during a family outing. Apparently the dog's name was given before this episode. Most of the western Tank Mountains, including the White Tanks area, lies within the east arm of the Yuma Proving Ground, and access is restricted. The Proving Ground boundary is not delineated by a fence, and warning signs are sparse. Access to the eastern Tank Mountains is provided by two primitive road systems which can be reached from a paved county road connecting the towns of Hyder and Dateland. These primitive roads, known to the locals as the "low road" and the "high road", can usually be negotiated with high-clearance two-wheel-drive vehicles well into the Tank Mountains, but local inquiry into their condition is recommended. The "low road" turns north from pavement near White Wing Ranch and follows Hoodoo Wash around the eastern termination of the Palomas Mountains, before it turns west and splits into a number of tracks that follow south-flowing washes draining the southeastern Tank Mountains. The "high road" runs north from pavement just east of White Wing Ranch about 15 miles before it turns west and splits into a number of tracks that can be followed southward from Palomas Plain into the Tank Mountains. The only connecting route between the "high road" and "low road" networks is at White Tanks on the Yuma Proving Ground, and this road is barely passable to even the most rugged 4-wheel drive vehicle. Bedrock geology of the eastern and central Tank Mountains, Yuma County, Arizona; report and two map sheets, scale 1:24,000.