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Characteristics of Southern California coastal aquifer systems

Brian D. Edwards, Randall T. Hanson, Eric G. Reichard and Theodore A. Johnson
Characteristics of Southern California coastal aquifer systems (in Earth science in the urban ocean; the Southern California continental borderland, Homa J. Lee (editor) and William R. Normark (editor))
Special Paper - Geological Society of America (2009) 454: 319-344


Most groundwater produced within coastal Southern California occurs within three main types of siliciclastic basins: (1) deep (>600 m), elongate basins of the Transverse Ranges Physiographic Province, where basin axes and related fluvial systems strike parallel to tectonic structure, (2) deep (>6000 m), broad basins of the Los Angeles and Orange County coastal plains in the northern part of the Peninsular Ranges Physiographic Province, where fluvial systems cut across tectonic structure at high angles, and (3) shallow (75-350 m), relatively narrow fluvial valleys of the generally mountainous southern part of the Peninsular Ranges Physiographic Province in San Diego County. Groundwater pumped for agricultural, industrial, municipal, and private use from coastal aquifers within these basins increased with population growth since the mid-1850s. Despite a significant influx of imported water into the region in recent times, groundwater, although reduced as a component of total consumption, still constitutes a significant component of water supply. Historically, overdraft from the aquifers has caused land surface subsidence, flow between water basins with related migration of groundwater contaminants, as well as seawater intrusion into many shallow coastal aquifers. Although these effects have impacted water quality, most basins, particularly those with deeper aquifer systems, meet or exceed state and national primary and secondary drinking water standards. Municipalities, academicians, and local water and governmental agencies have studied the stratigraphy of these basins intensely since the early 1900s with the goals of understanding and better managing the important groundwater resource. Lack of a coordinated effort, due in part to jurisdictional issues, combined with the application of lithostratigraphic correlation techniques (based primarily on well cuttings coupled with limited borehole geophysics) have produced an often confusing, and occasionally conflicting, litany of names for the various formations, lithofacies, and aquifer systems identified within these basins. Despite these nomenclatural problems, available data show that most basins contain similar sequences of deposits and share similar geologic histories dominated by glacio-eustatic sea-level fluctuations, and overprinted by syndepositional and postdepositional tectonic deformation. Impermeable, indurated mid-Tertiary units typically form the base of each siliciclastic ground-water basin. These units are overlain by stacked sequences of Pliocene to Holocene interbedded marine, paralic, fluvial, and alluvial sediment (weakly indurated, folded, and fractured) that commonly contain the historically named "80-foot sand", "200-foot sand", and "400-foot gravel" in the upper part of the section. An unconformity, cut during the latest Pleistocene lowstand (delta (super 18) O stage 2; ca. 18 ka), forms a major sequence boundary that separates these units from the overlying Holocene fluvial sands and gravels. Unconfined aquifers occur in amalgamated coarse facies near the bounding mountains (forebay area). These units are inferred to become lithologically more complex toward the center of the basins and coast line, where interbedded permeable and low-permeability alluvial, fluvial, paralic, and marine facies contain confined aquifers (pressure area). Coastal bounding faults limit intrabasin and/or inter-basin flow in parts of many basins.

ISSN: 0072-1077
EISSN: 2331-219X
Serial Title: Special Paper - Geological Society of America
Serial Volume: 454
Title: Characteristics of Southern California coastal aquifer systems
Title: Earth science in the urban ocean; the Southern California continental borderland
Author(s): Edwards, Brian D.Hanson, Randall T.Reichard, Eric G.Johnson, Theodore A.
Author(s): Lee, Homa J.editor
Author(s): Normark, William R.editor
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Pages: 319-344
Published: 2009
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 97
Accession Number: 2009-074436
Categories: Hydrogeology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 4 tables, sketch maps
N32°45'00" - N34°45'00", W121°00'00" - W116°00'00"
Secondary Affiliation: Bedford Institute of Oceanography, CAN, CanadaWater Replenishment District of Southern California, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200940
Program Name: USGSOPNon-USGS publications with USGS authors
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