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Geologic Framework and Hydrostratigraphy of the Edwards and Trinity Aquifers Within Hays County, Texas

Scientific Investigations Map 3540
Prepared in cooperation with the Edwards Aquifer Authority
By: , , and 
https://doi.org/10.3133/sim3540

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Abstract

During 2023–24, the U.S. Geological Survey, in cooperation with the Edwards Aquifer Authority, revised a previous publication of the geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers that was completed during 2018 within Hays County, Texas. The purpose of this report is to present the updated geologic framework and hydrostratigraphy of the rocks containing the Edwards and Trinity aquifers in Hays County from field observations of the surficial expressions of the rocks. The report includes a detailed 1:24,000-scale hydrostratigraphic map with names and descriptions of the geologic framework and hydrostratigraphic units (HSUs) in the study area. The study includes updates to the interpretation of the Kainer Formation of the Edwards Group with the addition of a burrowed unit between the basal nodular and dolomitic members. Hydrostratigraphy was also updated with the addition of the Seco Pass HSU for the burrowed member of the Kainer Formation. The study also includes updates to the interpretation of the hydrostratigraphy of the Trinity aquifer with the addition of the cavernous HSU at the top of the upper zone of the Trinity aquifer and the Herff Falls HSU between the Bulverde and Rust HSUs of the middle zone of the Trinity aquifer.

This updated report provides additional information about a complex aquifer system. The complexity in the aquifer system results from a combination of the original depositional history, bioturbation, development of primary and secondary porosity, postdepositional diagenesis, fracturing, and faulting.

Suggested Citation

Clark, A.K., Morris, R.R., and Lamberts, A.P., 2025, Geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within Hays County, Texas: U.S. Geological Survey Scientific Investigations Map 3540, 1 sheet, scale 1:24,000, 13-p. pamphlet, https://doi.org/10.3133/sim3540. [Supersedes USGS Scientific Investigations Map 3418.]

ISSN: 2329-132X (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Geologic Framework
  • Hydrostratigraphy
  • Implications of Hydrostratigraphic Characteristics and Geologic Structure on Groundwater Recharge and Flow Paths
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within Hays County, Texas
Series title Scientific Investigations Map
Series number 3540
DOI 10.3133/sim3540
Publication Date August 22, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Oklahoma-Texas Water Science Center
Description Pamphlet: viii, 13 p.; 1 Sheet: 49.01 x 39.15 inches; Data Release
Country United States
State Texas
County Hays County
Online Only (Y/N) Y
Additional publication details