This map depicts the geology of the Land 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 much of the San Pedro River corridor. 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 1:24,0 00-scale geologic maps that have been completed recently in the upper San Pedro Valley. Other maps cover the Fairbank (Ferguson et al, 2006), Lewis Springs (Pearthree et al. 2005), Saint 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 199 2.

The Saint David 7½' Quadrangle is located approximately 55 miles (88 km) west of downtown Tucson. The map area encompasses the town of Saint David, a portion of the San Pedro River corridor, and the western piedmonts of the Little Dragoon and Dragoon Mountains. The San Pedro River flows north from Mexico to the Gila River. It occupies a broad valley inset below adjacent Pleistocene piedmont alluvial fans. The river is incised several meters below adjacent terraces and recently abandoned floodplains. Entrenchment occurred between 1890 and 1908 as a result of a series of large floods in conjunction with changing land uses and population growth (Hereford, 1993). Once entrenched the channel widened to its current width and eventually stabilized in the mid-1950s (Hereford, 1993).

The Wintersburg 7½' quadrangle is located 40 to 50 miles (70-80 km) west of downtown Phoenix. The map area covers much of the piedmont between the Palo Verde Hills and the Hassayampa River and a 7 mile (11 km) reach of the Hassayampa River. The quadrangle includes a portion of the Palo Verde Nuclear Generating Station (PVNGS) and Interstate Highway 10. It has experienced some suburban development associated with the PVNGS and is currently on the outer fringe of the greater Phoenix metropolitan area, so more development is likely in the near future. The small bedrock hills in the southwestern quarter of the quadrangle were mapped by Charles Ferguson in the spring of 2005. Surficial deposits that cover most of the quadrangle were mapped by Philip Pearthree using color aerial photos from 1979, high-resolution digital color orthophotos provided by the Flood Control District of Maricopa County (FCDMC), and topographic information. Field checking was done in the spring, summer and fall of 2005. This mapping was done in conjunction with geologic mapping of the Flatiron Mountain 7½' quadrangle (Spencer et al, 2005) to the north, and this quadrangle map is one of eight 1:24,000 scale geologic maps covering most of the Hassayampa Valley that have been produced in 2004 - 2006. This mapping was completed under the joint State-Federal STATEMAP program, as specified in the National Geologic Mapping Act of 1992.

Geomorphologic analyses and surficial geologic mapping provide information about the age and type of alluvial deposits on piedmonts that is critical in assessing the character of piedmont landforms and the nature and extent of piedmont flood hazards. Piedmonts in Maricopa County are covered by complex mosaics of surficial deposits with different physical characteristics related to the ages of the deposits. Surficial geologic maps differentiate alluvial deposits based on physical characteristics of the deposits (sediment size and character) and geomorphic characteristics of the upper surfaces of the deposits. Differences in the primary physical characteristics of surficial deposits result from differences in rock types in drainage basins and differences in the size and character of the stream system that transported the sediment. Surficial deposits are subsequently altered by processes including weathering, soil development, and local erosion, so the character of the surface and near-surface portion of the deposits is related to the length of time that the deposits have been exposed at the surface. Simply stated, active fluvial systems leave behind evidence of their activity in the form of young deposits. Thus, surficial geologic maps are very useful in defining the physical framework of active fluvial systems on piedmonts.

Structural measurements of deformation fabrics in Paleoproterozoic rocks within the map area were plotted on stereonets using Rick Allmendinger’s Stereonet software provided on his Cornell University website (www.geo.cornell.edu/geology/faculty/RWA/programs.html). One map sheet and a second sheet with geochemical data and plots, structural stereonets and three cross-sections.

The Peppersauce Wash 7 ½' Quadrangle and the southwestern part of the Kielberg Canyon 7 ½' Quadrangle include part of the San Pedro River lowlands, flanking valley fill on both sides of the river, and limited bedrock outcrops (Fig. 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 07HQAG0110. Mapping was developed from previous mapping, new field investigations, and interpretation of color orthophotography taken in 2007. Mapping was compiled digitally using ESRI ArcGIS software.

The Clark Ranch 7½' Quadrangle and the western half of the Rhodes Peak 7½' Quadrangle include part of the San Pedro River, flanking valley fill, and bedrock on the east side of the valley that forms part of the Galiuro Mountains range front (Fig. 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 07HQAG0110. Mapping was compiled digitally using ESRI ArcGIS software. Parts of the Clark Ranch and Rhodes Peak Quadrangles were mapped previously by Creasey et al. (1961), Dickinson (1987, 1991, 1998), Marsh (2001), and Skotnicki (undated)). Studies of Cenozoic sedimentary strata in the Clark Ranch 7½' Quadrangle include those by Blake (1902, 1903), Bollaert (1952, 1953, 1962), Heindl (1963), Agenbroad (1967), Krieger et al. (1974), Ladd (1975), Scarborough and Wilt (1979), Utley (1980), Lindsay (1984), Dickinson (1988), Shenk (1990), and Dickinson (2003). The regional geochronology of the Oligo-Miocene volcanic rocks is outlined by Dickinson and Shafiqullah (1989). Studies of the Copper Canyon mineral district include those by Marsh (2001), Creasey et al., (1981), Guthrie (1994), Guthrie and Moore (1978), Hausen et al. (1988), Walker (1979) and Eichenlaub and Seedorff (2008).

The Lookout Mountain 7½' Quadrangle includes part of the San Pedro River lowlands, flanking valley fill, and bedrock on the west side of the valley that forms the eastern Black Hills and southeastern-most Tortilla Mountains (Fig. 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 07HQAG0110. Mapping was compiled digitally using ESRI ArcGIS software. Plate 1 contains two cross sections.

These geologic map sheets and report encompass the proposed State Route 95 Relocation Corridor in Mohave Valley, western Arizona, between the Black Mountains on the east and the Colorado River on the west (Figure 1). The maps were developed through compilation of existing geologic mapping and extensive new geologic mapping. The map area includes a portion of the historical floodplain of the Colorado River, a broad swath of the piedmont east of the river, parts of western flank of the Black Mountains, the channels and terraces of Sacramento Wash, and the northernmost piedmont of the Mohave Mountains (the Powell Mountain area). The corridor is predominantly covered with late Miocene and younger alluvium deposited by local tributary washes and the Colorado River. Deposits range in age from modern to at least 8 Ma (millions of years ago), 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 or the northern end of the Mohave Mountains. The northern, northeastern, and southernmost parts of the map include a variety of bedrock types ranging in age from early Proterozoic to middle Miocene. This map and report describe the physical characteristics of geologic units of different ages and sources, the mapped extent of various geologic units, and potential geologic resource and geologic hazard implications of this mapping. These maps include modified versions of portions of several published maps that have been completed in this area since 1997 (Howard et al., 1997; Howard et al., 1999; Faulds et al., 2001; Murphy et al., 2004; Pearthree and House, 2005; Pearthree, 2007; Spencer et al., 2007; Malmon, in review). Extensive new surficial geologic mapping and bedrock mapping was done where needed.

This report and accompanying maps describe the geology, geomorphology, and geologic hazards of the Maricopa area in western Pinal County, central Arizona. This mapping covers all of the Antelope Peak NE 7 ½’ quadrangle and most of the Maricopa 7 ½’, and includes the community of Maricopa (Figure 1). The map area encompasses part of the basin floor occupied by Santa Rosa Wash and the Santa Cruz River, the gently sloping piedmonts flanking the west side of the basin floor, and a few bedrock hills (inselbergs) outboard from the Haley Hills, Palo Verde Mountains and Table Top Mountains to the west and southwest of the map area. Agricultural activity and more recently urban development have substantially modified the surface of the basin floor and most of the piedmont areas. Maricopa is developing into a significant population center and rapid development is occurring on the basin floor and the piedmont in the northern part of the map area. The map area includes part of the Maricopa- Stanfield sedimentary basin, from which tremendous amounts of ground water have been extracted primarily for agricultural purposes