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Water wells in the lower Trinity (Twin Mountains and Travis Peak), Mills County, Texas

Home water wells that draw from the lower Trinity (Twin Mountains and Travis Peak) in Mills County, Texas are typically 202 to 402 feet deep (median 310 ft, 157 wells drilled in the last 10 years). It is the county's main layer: 88% of the 178 wells the state's model covers. They are about as deep as the county's median well (300 ft). Estimated cost of a complete well at the median depth: $10,500 to $25,000.

Updated every day from Texas Water Development Board driller reports. Last update: November 11, 2026, using the state file of November 10, 2026.

All wells in Mills CountyLower Trinity (Twin Mountains and Travis Peak) across Texas

Which layer Mills County wells draw from

Under Goldthwaite, Mills County

County home wells covered by the Northern Trinity and Woodbine model (in the last 10 years).

Home wells in Mills County

Each dot is a home well from a state driller report, colored by depth. Tap one for its details and official report. Tap an empty spot to see what is under that point.

See underground

Well depth (ft)

  • <100
  • 100
  • 200
  • 300
  • 400
  • 600
  • 800+

Dark line: Mills County

Key figures

Typical depth (middle half)
202 to 402 feet
Median depth
310 feet
Deepest 10% are past
470 feet
Water level (median)
170 feet
109 wells
Yield (median)
15 gpm
139 wells, gallons per minute
Wells used
157
In the last 10 years
Share of the county's wells
88%
All years on file
401
median 300 ft, since 2001
Confidence
Standard (30 or more wells)

When the wells were finished, the water stood a median 170 feet below the surface (109 wells).

Which layer Mills County wells draw from

County home wells covered by the Northern Trinity and Woodbine model (in the last 10 years).

What this layer is

This group is the lower half of the Trinity in North and Central Texas, the Twin Mountains Formation in the north and the Travis Peak to the south: the Hensell sand, the Pearsall shale and limestone, and the Hosston sandstone and conglomerate at the bottom. The state's model draws three layers, each at least 30 feet thick. This atlas reports them together because the method cannot place a well in one of the three reliably. North and west of Fort Worth they are the lower part of the undivided Antlers Formation.

More about the lower Trinity (Twin Mountains and Travis Peak)

Depth over time

Home well depth in this layer in Mills County has not changed meaningfully in 20 years: the median was 270 feet in 2003 to 2007 and 310 feet in 2021 to 2025 (a difference under 10% or within the margin of error).

PeriodMedian depth (ft)Wells
2001–200526473
2006–2010284119
2011–201532045
2016–202031548
2021–2025310104
202623012

Places in Mills County with wells in this layer

Common questions

How deep is a well in the lower Trinity (Twin Mountains and Travis Peak) in Mills County?

Home water wells that draw from the lower Trinity (Twin Mountains and Travis Peak) in Mills County, Texas are typically 202 to 402 feet deep (median 310 ft, 157 wells drilled in the last 10 years).

How many Mills County wells draw from this layer?

It is the county's main layer: 88% of the 178 wells the state's model covers. For 93% of these wells the report says where the water enters (the screen or the open hole), and we use the middle of that interval.

How deep does the water stand?

When the wells were finished, the water stood a median 170 feet below the surface (109 wells).

What a well costs here

At the median depth for this layer in Mills County (310 feet), a complete home well would cost roughly $10,500 to $25,000: $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 (202 to 402 feet) the range runs from $7,500 to $30,500. 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 93% of these wells the report says where the water enters (the screen or the open hole), and we use the middle of that interval.

How well it works: In 7,977 wells in the area of the state's Northern Trinity and Woodbine model (North and Central Texas) where the State of Texas recorded the aquifer, our estimate of the formation the well draws from names the same layer of the state's model in about 74% of them, and that layer or the one next to it in at least 95%; among the 3,130 of those wells that the state places in a Trinity layer (Paluxy to Hosston) it is about 56%.

  • The layers come from the Texas Water Development Board's Northern Trinity and Woodbine model, with quarter mile cells, summarized here to about 1.3 miles. It is a regional model, not a survey of any lot: between one model point and the next, the real depth of each layer can differ.
  • In this model every layer is at least 30 feet thick, even where the real rock is thinner or missing. Thin layers and the edges of the model are approximate.
  • Inside the Trinity this atlas does not name single model layers: it groups the Paluxy and Glen Rose (upper Trinity) and groups the Hensell, Pearsall and Hosston (lower Trinity, Twin Mountains and Travis Peak), because the check against the state's codes shows the method cannot separate them reliably.
  • "Near or below the base of the Trinity" means the well reaches the bottom of the model or passes it, often by tens of feet. Older rock that the model does not include may lie there.
  • 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/mills-county/twin-mountains. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.

Sources