Edwards-Trinity and Rita Blanca (Cretaceous rock under the Ogallala): how deep the wells are

What this layer is

Under the Ogallala, in many places, lie Cretaceous rocks: the Antlers (Trinity) sand and the Edwards limestones. They form the Edwards-Trinity (High Plains) Aquifer around and south of Lubbock and the Edwards-Trinity (Plateau) Aquifer around Midland and Odessa, and older Cretaceous and Jurassic sandstones form the Rita Blanca Aquifer in Dallam and Hartley counties. Many home wells in Midland, Martin, Terry, Lynn and Hockley counties draw from them.

Units the model puts in this layer: Cretaceous (Dakota, Purgatoire) and Jurassic (Morrison, Exeter) sandstones under the Ogallala in Dallam and Hartley counties; Lower Cretaceous: Antlers (Trinity) Sand and Fredericksburg Group limestones (Edwards), under the Ogallala; Edwards-Trinity (High Plains) around Lubbock, Edwards-Trinity (Plateau) around Midland and Odessa.

Source of the layers: TWDB's High Plains Aquifer System model, with half mile cells, read here on a grid of about 1.2 by 1.4 miles.

Key figures

Typical depth (middle half)

110 to 205 feet

Median depth

163 feet

Deepest 10% are past

243 feet

Water level (median)

112 feet

925 wells

Yield (median)

20 gpm

1,419 wells, gallons per minute

Wells used

5,214

In the last 10 years

All years on file

13,365

median 151 ft, since 2001

Confidence

Standard (30 or more wells)

Common questions

What a well in this layer costs

At the median depth for this layer (163 feet), a complete home well would cost roughly $6,500 to $16,500: $25 to $60 per foot for drilling, casing and seal, plus $2,500 to $6,500 for the pump, pressure tank, controls and hookup at the well. Across the whole middle half of depths (110 to 205 feet) the range runs from $5,500 to $19,000. This is TerraFunded's estimate from published Texas prices, not a quote, and it leaves out trenching and the line to the house. Get prices from at least two licensed drillers.

How these numbers are made

We count new and replacement domestic (home) wells with a valid depth on their report. We use the last 10 years when there are at least 30 wells; otherwise all since 2001. The median is the middle well and the middle half runs from the 25th to the 75th percentile.

To tell which layer a well draws from, we take the ground elevation at its location, subtract the depth of the interval where water enters (or the bottom of the hole when the report does not give one) and see which layer of the state's model that point falls in.

For 88% of these wells the report says where the water enters and we use the middle of that interval; for the rest we use the bottom of the hole, which tends to read one layer too deep.

How well it works: In 22,814 wells in the Texas part of the state's High Plains Aquifer System model (the Panhandle, the South Plains and the Permian Basin) where the State of Texas recorded the aquifer, the formation our method says the well draws from (as grouped on these pages) is the one the state recorded in about 75% of them; when it names the Dockum (4,542 wells), the state's record agrees only about 33% of the time, and most of the others are recorded as Ogallala wells.

• The layers come from the Texas Water Development Board's High Plains Aquifer System model, with half mile cells, read here on a grid of about 1.2 by 1.4 miles. It is a regional model, not a survey of any lot.
• The state's model has half mile cells; we read it on a grid of about 1.2 by 1.4 miles, Texas part only. Layers from version 1.01 (2015); the 2025 extension (1.02) did not change them. It is not a survey of any lot, so we give ranges.
• Figures go by four groups: Ogallala; Pecos Valley; Edwards-Trinity and Rita Blanca (Cretaceous rock under the Ogallala; the Rita Blanca alone matched the state 19%); Dockum (upper and lower together: the state's codes almost never say which). The Edwards-Trinity group joins three aquifers in different places (High Plains around Lubbock, Plateau around Midland and Odessa, Rita Blanca in Dallam and Hartley): county and place pages name the local one where they can.
• Dockum: when our method names the Dockum, the state's record agrees only 33% of the time over all years (61% for wells with a screened interval, which is 93% of home wells of the last 10 years); most of the rest are recorded as Ogallala wells. The median well we put in the Dockum ends about 18 ft under the base of the Ogallala as the model draws it. So these pages say "at or just below the base of the Ogallala, in the top of the Dockum", never a certain formation. The state's own 2025 report on this model says depth alone overstates the upper Dockum.
• "Near or below the base" means the well ends near or below the base of the Dockum, or of the Ogallala where there is no Dockum (Permian red beds; Gray, Carson, Donley, Moore and north Potter counties). Half of these wells end within about 51 ft of the base, and the state usually records them as Ogallala or Dockum wells. That is not an error: the model simply ends there.
• For old wells without a screened interval (bottom of the hole) the method is only a little better than always saying Ogallala (65% against 58%); with an interval it is 89% against 80%. Figures over all years carry that weakness; last 10 years figures rest almost entirely on intervals.
• We never use the model's water levels. The water level on this page is the one each driller measured when the well was finished.

These are depths of real wells drilled nearby, not a promise about any property. Groundwater can change over short distances and with drought. A licensed water well driller can tell you what to expect on a specific tract.

Read the full methodology · Download the data (CSV, CC BY 4.0)

How to cite

TerraFunded (2026). Texas Well Atlas: Underground. From Texas Water Development Board driller reports and groundwater availability models (data as of November 10, 2026). https://terrafunded.com/wells/formations/edwards-trinity. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.

Sources

• Submitted Driller's Reports database, Texas Water Development Board (TWDB) (file of November 10, 2026)
• Numerical Model Report for the High Plains Aquifer System Groundwater Availability Model. Deeds, N.E., and Jigmond, M. (INTERA Incorporated), for the Texas Water Development Board; extension through 2020 by Cawthon, T., and Wade, S. (TWDB, 2025), 2015, GAM v1.01 (layers unchanged in the 2025 extension, version 1.02). TWDB groundwater availability model.
• Ground elevation: Terrain Tiles (Mapzen), Registry of Open Data on AWS
• TWDB well report viewer (each well's official report)