Geologic Map of the Wintersburg 7.5' Quadrangle, Maricopa County, Arizona, v. 1.0
KeywordsArizona Geological Survey Digital Geologic Maps
Palo Verde Hills
Palo Verde Nuclear Generating Station
Palo Verde Basin
giant desiccation cracks
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CitationPearthree, Philip A., Ferguson, Charles A., and Harris, Raymond C., 2006, Geologic Map of the Wintersburg 7.5' Quadrangle, Maricopa County, Arizona: Arizona Geological Survey Digital Geologic Map DGM-47, version 1.0, map scale 1:24,000.
DescriptionThe 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.
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STRUCTURAL GEOLOGY AND TECTONIC EVOLUTION OF THE NORTHEASTERN RINCON MOUNTAINS, COCHISE AND PIMA COUNTIES, ARIZONALingrey, Steven Howard (The University of Arizona., 1982)The northeastern Rincon Mountains record a superposed history of low-angle normal-slip shear strain. Moderate- to low-angle faults, mapped previously as Laramide thrust faults, are recognized as normal faults of Tertiary age. Two faults are predominant: a younger-overolder ductile fault forms the base of a metasedimentary carapace, a ductile shear zone (decollement zone) of southwest vergent slip, and an older-over-younger (locally younger-over-older) fault named herein as the San Pedro basal detachment fault forms a brittle shear surface of west-southwest slip. The decollement zone is characterized by passive-slip folding, flexural-flow folding, boudinage, stretched pebbles, and low-angle ductile normal faults. Structural analysis reveals southwest- ergent simple shear strain with a component of superimposed pure shear strain (vertical flattening). The San Pedro basal etachment fault underlies a faulted, distended allochthon. The internal structure of the allochthon is characterized by an imbricate shingling of tilted fault blocks against west-dipping normal faults, suggesting emplacement from the east by an extensional and/or gravitional mechanism. Detachment faulting involved Late Oligocene sedimentary rocks yet cuts ∼26 m.y. old dikes. Mid-Miocene (?) faults form north-trending fault blocks which have rotated rocks of the metamorphic basement and the allochthon eastward. High-angle normal faults of the Basin and Range disturbance form an eastern fault margin across which the northeastern Rincon Mountains have been uplifted. The deformation recorded in the northeastern Rincon Mountains is interpreted to reflect mid-Tertiary crustal extension. Early structural elements define a ductile shear zone which is either truncated or overprinted by a subsequently thinner zone of brittle shear. The shear zone descends stratigraphically westward across the Rincon Mountains. Reconstructions of its mid-Tertiary configuration show the shear zone to be a surface of normal-slip. Displacement near the surface is by brittle shear, but is progressively replaced by ductile shear down-dip. Evolution of the surface superimposes the region of brittle shear against the region of ductile shear. Late Cenozoic block faulting has segmented, tilted, and exhumed the surface.