Geologic Framework and Hydrostratigraphy of the Edwards and Trinity Aquifers Within Northern Bexar and Comal Counties, Texas

Scientific Investigations Map 3510
Prepared in cooperation with the Edwards Aquifer Authority
By: , and 

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Abstract

During 2020–22, the U.S. Geological Survey, in cooperation with the Edwards Aquifer Authority, revised a previous publication that described the geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within northern Bexar and Comal Counties, Texas. This report presents the refined maps and descriptions of geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within northern Bexar and Comal Counties that resulted from additional field data. Two informal geologic units and their corresponding informal hydrostratigraphic unit (HSU) names are introduced in this report; these informal units were identified during geologic mapping work done in counties adjoining the study area. Hydrostratigraphically, the rocks exposed in the study area represent a section of the upper confining unit to the Edwards aquifer, the Edwards aquifer, the upper zone of the Trinity aquifer, the middle zone of the Trinity aquifer, and the lower confining unit to the middle zone of the Trinity aquifer. The Washita, Eagle Ford, Austin, and Taylor Groups are generally considered to be the upper confining unit to the Edwards aquifer. The Edwards aquifer was subdivided into nine informally named HSUs (from top to bottom) as follows: I, II, III, IV, V, VI, VII, Seco Pass, and VIII. The upper zone of the Trinity aquifer was subdivided into five informal HSUs and two subunits (from top to bottom) as follows: cavernous, Camp Bullis, upper evaporite, fossiliferous (subunits: upper and lower), and lower evaporite. The middle zone of the Trinity aquifer was subdivided into nine named HSUs (from top to bottom) as follows: Bulverde, Little Blanco, Twin Sisters, Doeppenschmidt, Herff Falls (where present), Rust, Honey Creek, Hensell, and Cow Creek. The middle zone of the Trinity aquifer is underlain by the confining Hammett HSU. Groundwater recharge and flow paths in the study area are influenced not only by the hydrostratigraphic characteristics of the individual HSUs but also by faults and fractures.

Suggested Citation

Clark, A.K., Golab, J.A., Morris, R.R., and Pedraza, D.E., 2023, Geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within northern Bexar and Comal Counties, Texas: U.S. Geological Survey Scientific Investigations Map 3510, 1 sheet, scale 1:24,000, 24-p. pamphlet, https://doi.org/10.3133/sim3510

ISSN: 2329-132X (online)

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Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Geologic Framework
  • Hydrostratigraphy
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within northern Bexar and Comal Counties, Texas
Series title Scientific Investigations Map
Series number 3510
DOI 10.3133/sim3510
Year Published 2023
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Oklahoma-Texas Water Science Center
Description Report: viii, 24 p., 1 Sheet: 68.19 × 50.65 inches; Data Release
Country United States
State Texas
County Bexar County, Comal County
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
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