More than 11,500 well records, such as geophysical logs, drilling descriptions, and published hydrogeologic framework information, were evaluated to help characterize the framework of hydrogeologic units in and near Gaines, Terry, and Yoakum Counties, Texas. Additional geophysical data were collected to improve the spatial coverage across the study area and to reduce uncertainty with regard to hydrogeologic unit extents. The evaluation of existing data plus the collection of new geophysical data provided that basis for developoing a refined understanding of how the saturated thickness of the Ogallala and Edwards-Trinity aquifers vary throughout the study area.

Declining groundwater levels in and near Gaines, Yoakum, and Terry Counties in the Texas Panhandle have raised concerns about the amount of available groundwater and the potential for water-quality changes resulting from dewatering and increased vertical groundwater movement between adjacent water-bearing hydrogeologic units. More than 9,800 well records, such as geophysical logs, drilling descriptions, and published hydrogeologic framework information, were evaluated to help characterize the framework of hydrogeologic units in the study area. Additional geophysical data were collected to improve the spatial coverage across the study area and to reduce uncertainty with regard to hydrogeologic unit extents. Of greatest interest was gaining a refined understanding of how the saturated thickness of the Ogallala and Edwards-Trinity aquifers vary throughout the study area.

In cooperation with the Llano Estacado Underground Water Conservation District (LEUWCD), the Sandy Land Underground Water Conservation District (SLUWCD), and the South Plains Underground Water Conservation District (SPUWCD), the U.S. Geological Survey (USGS) compiled historical geophysical and geochemical data in Gaines, Yoakum, and Terry Counties, Texas, and collected additional data where gaps were evident to assist with building a conceptual hydrogeologic model of the Gaines, Yoakum, and Terry Counties region. The compiled historical data includes all data available from predevelopment (pre-1945) through present day. For this study, predevelopment is considered everything prior to 1945 when the large-scale groundwater extractions for agricultural purposes started. The use of center pivot irrigation and the adaptation of automotive engines for groundwater wells had a large impact on the regional groundwater system around 1945. The compiled historical data included well-construction information, previously measured water level and water quality data, and hydraulic-properties testing data (slug tests, aquifer tests, pump tests, and so forth.). Additionally, the USGS collected surface time-domain electromagnetic soundings, borehole geophysical logs, and water-quality samples to develop and refine the hydrogeologic framework of the area. This data release includes all of the compiled historical water-level and water quality data, as well as geophysical data collected for the study.

This data release supports the U.S. Geological Survey Scientific Investigation Map (SIM) by Clark and others (2020) by documenting the data used to create the geologic maps and describe geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers for a 442 square-mile area in northern Medina County in south Texas. The karstic Edwards and Trinity aquifers that are the subject of the SIM by Clark and others (2020) are classified as major sources of water in south-central Texas by the Texas Water Development Board (George and others, 2011). The geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers largely control groundwater-flow paths and storage in northern Medina County (Kuniasky and Ardis, 2004). The data provided in this data release and the detailed maps and descriptions of the geologic framework and hydrostratigraphy in Clark and others (2020) are intended to help provide water managers information that is useful for effectively managing available groundwater resources in the study area. These digital data accompany Clark, A.K., Morris, R.E., and Pedraza, D.E., 2020, Geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within northern Medina County, Texas: U.S. Geological Survey Scientific Investigations Map 3461, 13 p. pamphlet, 1 pl., scale 1:24,000, https://doi.org/10.3133/sim3461.

The karstic Edwards and Trinity aquifers are classified as major sources of water in south-central Texas by the Texas Water Development Board, and both are classified as major aquifers by the State of Texas. The Edwards and Trinity aquifers developed because of the original depositional history of the carbonate limestone and dolomite rocks that contain them, and the primary and secondary porosity, diagenesis, fracturing, and faulting that modified the porosity, permeability, and transmissivity of each aquifer and of the geologic units separating the aquifers. Previous studies such as those by the U.S. Geological Survey (USGS) and the Edwards Aquifer Authority (EAA) have mapped the geology, hydrostratigraphy, and structure in these areas at various scales. The purpose of this data release is to present the data that were collected and compiled to describe the geologic framework and hydrostratigraphy of northern Medina county, Texas in order to help water managers, water purveyors, and local residents better understand and manage water resources. The scope of the larger work and this accompanying data release is focused on the geologic framework and hydrostratigraphy of the outcrops and hydrostratigraphy of the rocks that contain the Edwards and Trinity aquifers within northern Medina county, Texas. These digital data accompany Clark and others (2024), which supersedes Scientific Investigations Map 3461.

This data release supports the U.S. Geological Survey Scientific Investigation Map (SIM) by Clark and others (2020) by documenting the data used to create the geologic maps and describe geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers for a 442 square-mile area in northern Medina County in south Texas. The karstic Edwards and Trinity aquifers that are the subject of the SIM by Clark and others (2020) are classified as major sources of water in south-central Texas by the Texas Water Development Board (George and others, 2011). The geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers largely control groundwater-flow paths and storage in northern Medina County (Kuniasky and Ardis, 2004). The data provided in this data release and the detailed maps and descriptions of the geologic framework and hydrostratigraphy in Clark and others (2020) are intended to help provide water managers information that is useful for effectively managing available groundwater resources in the study area. These digital data accompany Clark, A.K., Morris, R.E., and Pedraza, D.E., 2020, Geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within northern Medina County, Texas: U.S. Geological Survey Scientific Investigations Map 3461, 13 p. pamphlet, 1 pl., scale 1:24,000, https://doi.org/10.3133/sim3461.

The U.S. Geological Survey (USGS) undertook a 5-year study beginning in 2016 to assess groundwater availability for the aquifers proximal to the Gulf of Mexico from the Texas-Mexico border to the western part of the panhandle of Florida; these aquifers are collectively referred to as the coastal lowlands aquifer system. This study is one of several regional groundwater availability studies being done as part of the USGS Water Availability and Use Science Program. Groundwater from the coastal lowlands aquifer system is used mainly for public, irrigation, and industrial supply. Land-surface subsidence related to groundwater pumping is an issue of ongoing concern within this study area. During the first two years of the study, the team developed an updated conceptual model of the hydrogeologic framework of the aquifer system, which lead to initial estimates of major water budget components such as recharge, surface-water/groundwater exchange, and coastal discharge. This data release documents the hydrogeologic data that were compiled and used to define the hydrogeologic framework.

The karstic Edwards and Trinity aquifers are classified as major sources of water in south-central Texas by the Texas Water Development Board, and both are classified as major aquifers by the State of Texas. The purpose of this data release is to present the data that were collected and compiled to describe the geologic framework and hydrostratigraphy within parts of Bandera and Kendall Counties, Texas, in order to help water managers, water purveyors, and local residents better understand and manage water resources. The scope of the larger work and this accompanying data release is focused on the geologic framework and hydrostratigraphy of the outcrops and hydrostratigraphy of the Edwards and Trinity aquifers within parts of Bandera and Kendall Counties, Texas. These digital data accompany Clark and others (2024).

The karstic Edwards and Trinity aquifers are classified as major sources of water in south-central Texas by the Texas Water Development Board, and both are classified as major aquifers by the State of Texas. The purpose of this data release is to present the data that were collected and compiled to describe the geologic framework and hydrostratigraphy within parts of Bandera and Kendall Counties, Texas, in order to help water managers, water purveyors, and local residents better understand and manage water resources. The scope of the larger work and this accompanying data release is focused on the geologic framework and hydrostratigraphy of the outcrops and hydrostratigraphy of the Edwards and Trinity aquifers within parts of Bandera and Kendall Counties, Texas. These digital data accompany Clark and others (2024).

The karstic Edwards and Trinity aquifers are classified as major sources of water in south-central Texas by the Texas Water Development Board, and both are classified as major aquifers by the State of Texas. The Edwards and Trinity aquifers developed because of the original depositional history of the carbonate limestone and dolomite rocks that contain them, and the primary and secondary porosity, diagenesis, fracturing, and faulting that modified the porosity, permeability, and transmissivity of each aquifer and of the geologic units separating the aquifers. Previous studies such as those by the U.S. Geological Survey (USGS) and the Edwards Aquifer Authority (EAA) have mapped the geology, hydrostratigraphy, and structure in these areas at various scales. The purpose of this data release is to present the data that were collected and compiled to describe the geologic framework and hydrostratigraphy within Hays County, Texas in order to help water managers, water purveyors, and local residents better understand and manage water resources. The scope of the larger work and this accompanying data release is focused on the geologic framework and hydrostratigraphy of the outcrops and hydrostratigraphy of the rocks that contain the Edwards and Trinity aquifers within Hays County, Texas. These digital data are a revision to a previous publication of the geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers that was completed in 2018 within Hays County, Texas. These digital data accompany USGS Scientific Investigations Map 3540 (Clark and others, 2025), which supersedes USGS Scientific Investigations Map 3418.