KeywordsArizona Geological Survey Open File Reports
Picacho Peak State Park
Basin and Range Province
Santa Cruz River
Casa Grande Mountains
Silver Bell Mountains
MetadataShow full item record
CitationJackson, G., 1990, Surficial geologic maps of the Picacho Basin. Arizona Geological Survey Open File Report, OFR-90-02, 5 map sheets, map scale 1:24,000, 9 p.
PublisherArizona Geological Survey (Tucson, AZ)
DescriptionSurficial geologic maps of the Picacho Basin. The Picacho basin is a large and complex graben surrounded by horsts and half-horsts, which are now the Picacho, Casa Grande, Silverbell, and Sacaton mountains. It formed mainly in response to late Miocene extension. Internal drainage probably persisted until about 3 million years ago. Several thousand meters of sediments fill the basin; 2000 m of evaporites and claystone form the bulk of the basin fill (Scarborough and Pierce, 1978). The upper 200 meters or so of basin fill was deposited by a gradually aggrading, regionally integrated drainage system. Young alluvium of the Santa Cruz River is up to 30 m thick and is found within 3.2 km of the modern channel (Pool, 1986). Although the Picacho Basin does have external drainage, extremely low stream gradients and a lack of long-term downcutting have resulted in playa-like sediments, eolian deposits, and a lack of significant elevation differences between "terraces. Unlike basins upstream, the Picacho basin has not been incised significantly during the Quaternary. One report and 5 map sheets, 1:24,000 map scale. Scale 1:24,000
RightsArizona Geological Survey. All rights reserved.
Collection InformationDocuments in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact email@example.com.
North Bounding Coordinate32.9538
South Bounding Coordinate32.5009
West Bounding Coordinate-111.709
East Bounding Coordinate-111.165
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Earth-fissure movements associated with fluctuations in ground-water levels near the Picacho mountains, south-central Arizona, 1980-84Carpenter, Michael C. (The University of Arizona., 1993)The Picacho earth fissure transects subsiding alluvial sediments near the eastern periphery of the Picacho basin in southcentral Arizona. The basin has undergone land subsidence of as much as 3.8 m since the 1930's due to compaction of the aquifer system in response to ground-water-level declines that have exceeded 100 m. The fissure extends generally north-south for 15 km and exhibits horizontal tensile failure as well as up to 0.6 m of normal dip-slip movement at the land surface, with the west side of the fissure downthrown. The fissure was observed as early as 1927, following an earthquake, and is the longest earth fissure in Arizona. Vertical and horizontal displacements have been monitored along a line normal to the fissure. The survey line extends from a bedrock outcrop in the Picacho Mountains on the east, past an observation well near the fissure, to a point 1422 in to the west. From May 1980 to May 1984, the western, downthrown side of the fissure subsided 167 ±1.8 mm and moved 18 ±1.5 mm westward into the basin. Concurrently, the eastern, relatively upthrown side subsided 147 ±1.8 mm and moved 14 ±1.5 mm westward. Dislocation modeling of deformation along the survey line near the fissure suggests that dip-slip movement has occurred along a vertical fault surface that extends from the land surface to a depth of about 300 m. Slip was 9 mm from May to December 1980 and 9 mm from March to November 1981. Continuous measurements were made of horizontal movement across the fissure using a buried invar-wire horizontal extensometer, while water-level fluctuations were continuously monitored in four piezometers nested in two observation wells. The range of horizontal movement was 4.620 mm, and the range of water-level fluctuation in the nearest piezometer in the deeper alluvium was 9.05 m. The maximum annual opening of the fissure during the study period was 3.740 mm from March to October 1981, while the water-level declined 7.59 m. The fissure closed 1.033 mm from October 1981 to March 1982 while the water level recovered 6.94 m. Opening and closing of the fissure were smooth and were correlated with water-level decline and recovery, respectively, in the nearby piezometers. Pearson correlation coefficients between the water-level fluctuations in the deeper piezometers and horizontal movement ranged from 0.913 to 0.925. The correlogram of water-level decline as ordinate, versus horizontal strain as abscissa, exhibits hysteresis loops for annual cycles of water-level fluctuation as well as near-vertical excursions for shorter cycles of pumping and recovery.