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Lower Trinity (Twin Mountains and Travis Peak): how deep the wells are

Home water wells that draw from the lower Trinity (Twin Mountains and Travis Peak) in North and Central Texas are typically 200 to 455 feet deep (median 340 ft, 12,230 wells drilled in the last 10 years). In the state's model it is sandstone with shale and limestone. It carries the most weight in Callahan County (99% of its wells), Comanche County (96% of its wells) and Eastland County (91% of its wells). Estimated cost of a complete well at the median depth: $11,000 to $27,000.

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

Depth of wells in the lower Trinity (Twin Mountains and Travis Peak), by countyThe dot is the median and the bar the middle half for each county. The table below has the figures.02505007501,000 ftParkerParker: 200–340 ftParker: 240 ft240WiseWise: 160–320 ftWise: 200 ft200ErathErath: 300–420 ftErath: 380 ft380BurnetBurnet: 305–500 ftBurnet: 380 ft380HoodHood: 225–420 ftHood: 380 ft380WilliamsonWilliamson: 500–640 ftWilliamson: 550 ft550ComancheComanche: 100–240 ftComanche: 160 ft160HamiltonHamilton: 430–554 ftHamilton: 475 ft475MontagueMontague: 140–240 ftMontague: 180 ft180TravisTravis: 400–590 ftTravis: 490 ft490BellBell: 560–860 ftBell: 770 ft770LampasasLampasas: 241–410 ftLampasas: 310 ft310

Under Dennis, Parker County

Dot: median. Bar: middle half (25th to 75th percentile). Counties with the most wells in this layer.

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.

Units the model puts in this layer: Hensell Member of the Travis Peak (Twin Mountains) Formation; Pearsall Member; Cow Creek and Hammett members to the south; Hosston Member of the Travis Peak (Twin Mountains) Formation; Sycamore and Sligo to the south; lower part of the Antlers Formation in the north and west.

Source of the layers: TWDB's Northern Trinity and Woodbine model, with quarter mile cells, summarized here to about 1.3 miles.

Key figures

Typical depth (middle half)
200 to 455 feet
Median depth
340 feet
Deepest 10% are past
580 feet
Water level (median)
234 feet
7,104 wells
Yield (median)
20 gpm
9,794 wells, gallons per minute
Wells used
12,230
In the last 10 years
All years on file
22,843
median 340 ft, since 1975
Confidence
Standard (30 or more wells)

Counties where homes draw from this layer

Only counties with at least 10 wells in the layer. The share is of the county's wells that the model covers.

Depth of wells in the lower Trinity (Twin Mountains and Travis Peak), by countyThe dot is the median and the bar the middle half for each county. The table below has the figures.02505007501,000 ftParkerParker: 200–340 ftParker: 240 ft240WiseWise: 160–320 ftWise: 200 ft200ErathErath: 300–420 ftErath: 380 ft380BurnetBurnet: 305–500 ftBurnet: 380 ft380HoodHood: 225–420 ftHood: 380 ft380WilliamsonWilliamson: 500–640 ftWilliamson: 550 ft550ComancheComanche: 100–240 ftComanche: 160 ft160HamiltonHamilton: 430–554 ftHamilton: 475 ft475MontagueMontague: 140–240 ftMontague: 180 ft180TravisTravis: 400–590 ftTravis: 490 ft490BellBell: 560–860 ftBell: 770 ft770LampasasLampasas: 241–410 ftLampasas: 310 ft310
Dot: median. Bar: middle half (25th to 75th percentile). Counties with the most wells in this layer.
CountyMedian depth (ft)WellsShare of the county's wells
Parker County2402,52736%
Wise County2001,85454%
Erath County3801,33988%
Burnet County3801,33772%
Hood County38079482%
Williamson County55073760%
Comanche County16048196%
Hamilton County47543586%
Montague County18043560%
Travis County49033036%
Bell County77025850%
Lampasas County31025868%
Coryell County48024288%
Bosque County66021553%
Cooke County54019130%
Mills County31015788%
Eastland County10012091%
Somervell County50011280%
Jack County2008845%
Callahan County686899%
Brown County2296476%
Johnson County680494%
Tarrant County640453%
McLennan County1,1684450%
Palo Pinto County1203355%

Places where it is the main layer

Where it sits among the model's layers

From top to bottom, with the median depth of the home wells that draw from each:

Layer (state's model)RockMedian depth (ft)Wells
Above the Woodbineshale, chalk and marl1601,739
Woodbinesandstone with shale2601,037
Washita and Fredericksburglimestone, marl and clay2401,050
Upper Trinity (Paluxy and Glen Rose)sandstone, limestone and marl2809,322
Lower Trinity (Twin Mountains and Travis Peak)sandstone with shale and limestone34012,230

Depth over time

Home well depth in this layer has not changed meaningfully in 20 years: the median was 340 feet in 2003 to 2007 and 320 feet in 2021 to 2025 (a difference under 10% or within the margin of error).

PeriodMedian depth (ft)Wells
2001–20053403,004
2006–20103404,016
2011–20153602,977
2016–20203564,856
2021–20253207,178
2026310797

Common questions

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

Home water wells that draw from the lower Trinity (Twin Mountains and Travis Peak) in North and Central Texas are typically 200 to 455 feet deep (median 340 ft, 12,230 wells drilled in the last 10 years).

What is the lower Trinity (Twin Mountains and Travis Peak)?

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.

How deep does the water stand in these wells?

When the wells were finished, the water stood a median 234 feet below the surface (7,104 wells).

What a well in this layer costs

At the median depth for this layer (340 feet), a complete home well would cost roughly $11,000 to $27,000: $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 (200 to 455 feet) the range runs from $7,500 to $34,000. 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 97% 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/formations/twin-mountains. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.

Sources