The Wildhorse Mountain 7 ½′ Quadrangle includes part of the central San Pedro River and flanking valley fill, as well as areas of bedrock on both sides of the valley and at the south edge of the Quadrangle where the San Pedro River crosses bedrock at the San Pedro Narrows (Figure 1). Production of this new geologic map continues the Arizona Geological Survey mapping program of the San Pedro River valley. This mapping was done under the joint State-Federal STATEMAP program, as specified in the National Geologic Mapping Act of 1992, and was jointly funded by the Arizona Geological Survey and the U.S. Geological Survey under STATEMAP Program Contract award number 06HQAG0051. Mapping was compiled digitally using ESRI ArcGIS software.

The Redington 7 ½' Quadrangle includes part of the northern San Pedro River and flanking valley fill, as well as two areas of bedrock on the east side of the valley (Figure 1). Production of this new geologic map continues the Arizona Geological Survey mapping program in the San Pedro River valley, and complements geologic mapping to the south of this quadrangle. The map area is located within the San Pedro River valley in the Basin and Range Province of southeastern Arizona. Oligocene to early Miocene, compositionally diverse volcanism in the Galiuro Mountains to the east of the map area occurred during the initiation of a period of severe tectonic extension that uncovered the Catalina-Rincon metamorphic core complex to the southwest (Dickinson and Shafiqullah, 1989; Dickinson, 1991). The San Pedro Valley was created in its basic form by this period of extensional faulting, which largely ended in the early to middle Miocene. Relative to this period of severe faulting, minor faulting affected the valley during late Miocene to Quaternary time, probably with declining activity over this time period. Laramide (latest Cretaceous to earliest Tertiary), steeply southwest dipping to locally overturned volcanic and sedimentary rocks are exposed over part of Redfield Canyon. These are overlain by gently dipping Oligocene to early Miocene Galiuro Volcanics. Tilting of the Laramide strata is thought to be Laramide, not middle Tertiary, because Galiuro Volcanics participated in the middle Tertiary extensional faulting in those areas where faulting occurred, and the Galiuro Volcanics that overlie the Laramide strata are only slightly tilted (Dickinson, 1991).

Southeastern Arizona hosts one of the greatest concentrations of copper deposits on Earth. After more than a hundred years of geologic study, the porphyry-style and related copper deposits of southeastern Arizona and elsewhere remain incompletely understood. Each deposit has unique features, including typically complex structure and diverse rock types that are affected by copper mineralization and associated alteration. Commonly, much of the information about these features is lost when the deposits are mined. The Rosemont copper-molybdenum skarn deposit is located in the subsurface of the northern Santa Rita Mountains, southeast of Tucson, Arizona. In order to evaluate the geologic setting of the deposit, the Arizona Geological Survey created a 1:12,000 scale geologic map of the rocks exposed on the surface above the deposit. This report and accompanying map are the products of that study. We thank Augusta Resource Corporation for providing access to the property and financial support.

This map depicts the geology of the Hereford and the northern part of the Stark 7 ½' quadrangles, which are located in the upper San Pedro Valley north of the U.S. - Mexico border. The quadrangles cover much of the piedmont east of the San Pedro River and southwest of Mule Mountains, including a portion of the San Pedro Riparian National Conservation Area along the river. The map also covers a small portion of the piedmont west of the San Pedro River. The geology of the quadrangle is diverse and includes Paleozoic sedimentary and igneous rocks, 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. Bedrock geologic mapping was compiled from Ferguson and Johnson (2006). This map is one of several 1:24,000-scale geologic maps that have been completed recently in the upper San Pedro Valley. Other maps cover the Lewis Springs (Pearthree et al., 2006), 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.

The Boundary Cone 7 ½' Quadrangle includes part of the Black Mountains and most of the piedmont between the Colorado River floodplain and the Black Mountains southeast of Bullhead City, Arizona. Production of this new geologic map continues the Arizona Geological Survey mapping program in the rapidly developing lower Colorado River corridor, and complements geologic mapping to the northwest and west of this quadrangle (Figure 1). This mapping was done under the joint State-Federal STATEMAP program, as specified in the National Geologic Mapping Act of 1992, and was jointly funded by the Arizona Geological Survey and the U.S. Geological Survey under STATEMAP Program Contract award number 05HQAG0078. Mapping was compiled digitally using ESRI ArcGIS software.

The Galleta Flat East 7.5' Quadrangle is located in northwestern Cochise County in southeastern Arizona, north of the town of Benson. The San Pedro River flows south to north across the quadrangle and has been in a downcutting phase during the Quaternary. Lower Quaternary and upper Pliocene strata, which are exposed in bluffs and low hills flanking the river, were deposited in fluvial and lacustrine-margin to playa environments (Smith, 1994; Youberg et al., 2003). Bedrock exposed near the northern end of the Quadrangle consists of early Proterozoic Johnny Lyon Granodiorite and Pinal Schist (Cooper and Silver, 1964; Drewes, 1974).

This map depicts the geology of the Fortuna 7 ½' Quadrangle and about 2.5 square miles of the northern end of the Gila Mountains that is in the adjacent Laguna Dam, Dome, and Ligurta 7 ½' Quadrangles. The map area encompasses the northwestern Gila Mountains and the broad Gila River valley between the northern Gila Mountains and Yuma, in the southwestern corner of Arizona. The quadrangle covers bedrock in the northwestern Gila Mountains, much of the western piedmont at the foot of the northwestern Gila Mountains, and alluvial sediments deposited by the Gila and Colorado Rivers. Large, active gravel quarries, and the historic Dome placer gold district, are within the map area at the foot of the Gila Mountains. This mapping was completed under the joint State-Federal STATEMAP program, as specified in the National Geologic Mapping Act of 1992.

The Needles NE 7 ½' Quadrangle includes the modern and historical floodplain of the Colorado River and the lower piedmont between the river and the Black Mountains to the east. This quadrangle is completely covered with late Cenozoic surficial deposits laid down by the Colorado River or its tributaries. Deposits range in age from modern to several million years old, and deposit characteristics and composition vary substantially depending on whether they were emplaced by the modern Colorado River, older versions of the river, or tributary washes derived from the Black Mountains. This map and report describe the physical characteristics of deposits of different ages and sources, the mapped extent of various deposits, and potential geologic resource and geologic hazard implications of this mapping.

Abstract: The Flatiron Mountain 7.5' Quadrangle is located approximately 70 km (40 miles) west of downtown Phoenix, and is just north of Interstate Highway 10. The map area includes the southeastern part of the Belmont Mountains and many isolated bedrock hills south and southeast of the Belmont Mountains. Most of the quadrangle, however, is underlain by Quaternary surficial deposits. Jackrabbit and Coyote washes, heading in the proximal piedmonts of the Big Horn Mountain northwest of the study area, are the major drainages. Jackrabbit Wash is incised up to four meters into older Pleistocene deposits. Coyote Wash flows around the Belmont Mountains and diverges into multiple channels to the south. The channels and floodplains of Coyote Wash are less incised than Jackrabbit Wash. Smaller tributary washes on adjacent older Pleistocene deposits generally are not incised more than two meters. Older Hassayampa River deposits are found along the eastern side of the quadrangle.

The geology of the Davis Dam SE quadrangle reflects the complex interplay of the Colorado River and piedmont drainages that flow from the Black Mountains to join the river. The history of the Colorado River in this area begins with the influx of water and sediment from the north about 5.5 Ma (House et. al., 2002). The first deposits associated with the river contain only locally-derived sediment from the northern part of Mohave Valley. These deposits are succeeded by the fine-grained Bouse Formation, which was probably deposited in a series of lakes as the developing Colorado River spilled over successive divides (Spencer and Patchette, 1997; House et al, 2002; Spencer and Pearthree, 2001). After the Colorado River was integrated through Mohave Valley, it entered a major phase of aggradation which resulted in the accumulation of about 800 feet of river sand and gravel that interfingers with tributary gravel and sand. By 3.3 Ma, the river had begun to incise into the valley fill and tributary deposits were cut into the uppermost part of the old river deposits. The river downcut to a level close to the modern river level by the early Quaternary, but subsequently there were at least 2 major aggradation events during the middle to late Quaternary. The modern channel is quite narrow and most of the historical floodplain has been developed, either as part of Bullhead City or as agricultural fields in the Fort Mohave Indian Reservation.