DFW Sits on Five Very Different Kinds of Ground
Drive west to east across the metroplex and you cross five geologic belts laid down by Cretaceous seas. Each one weathers into a different soil, and those soils behave completely differently under a rigid concrete pool shell.
On the east side, the Blackland Prairie's Houston Black clay, the official Texas state soil, is one of the most expansive soils in the United States. In a drought it opens cracks that USDA has documented at more than 80 inches deep. On the far west side of the metro, Cross Timbers sands barely move at all.
That is why a pool in McKinney and a pool in Weatherford can be the same age, built by the same builder, and be in completely different structural condition today.
Weatherford, Azle. Pack sands over sandstone. Lowest metro risk.
Fort Worth, mid-cities. Shallow clay over limestone and marl. Real movement, usually less extreme.
Grapevine, Keller, Flower Mound corridor. Sandy Woodbine soils. Moderate.
Irving, Grand Prairie, Arlington, west Dallas. Bentonitic residual clays with documented severe movement.
Eastern arc: Collin, Rockwall, east Dallas, Ellis, Kaufman counties. Houston Black clay. The worst in the metro.
Every DFW City, Rated for Pool Soil Risk
Ratings reflect the dominant soils and geology under each city's residential areas, normalized from USDA shrink-swell classifications. Many cities span more than one soil zone, so conditions vary lot to lot. Methodology and sources are at the bottom of this page.
Blackland Prairie & Eagle Ford Core
23 citiesDallas
Dallas Co · Blackland east, Eagle Ford west, chalk center. East and Southeast Dallas run worst.
Plano
Collin Co · Blackland Prairie clays
Frisco
Collin/Denton Co · Blackland; sandier far west
McKinney
Collin Co · Core Blackland Prairie
Allen
Collin Co · Core Blackland Prairie
Prosper
Collin/Denton Co · Blackland east, sandier west
Celina
Collin/Denton Co · Blackland east, sandier west
Murphy
Collin Co · Blackland Prairie
Wylie
Collin Co · Blackland Prairie
Sachse
Dallas/Collin Co · Blackland Prairie
Richardson
Dallas/Collin Co · Blackland with chalk transition
Garland
Dallas Co · Core Blackland Prairie
Rowlett
Dallas/Rockwall Co · Blackland Prairie
Rockwall
Rockwall Co · Entire county in the Blackland belt
Mesquite
Dallas Co · Core Blackland Prairie
Irving
Dallas Co · Eagle Ford Shale type area; bentonitic clays
Farmers Branch
Dallas Co · Blackland and chalk transition
Addison
Dallas Co · Blackland and chalk transition
Lancaster
Dallas Co · Southern Dallas Blackland
Forney
Kaufman Co · Blackland Prairie
Terrell
Kaufman Co · Blackland Prairie
Waxahachie
Ellis Co · Type area for Houston Black mapping
Ennis
Ellis Co · Blackland Prairie
Eagle Ford Edges, Chalk Escarpment & Mixed Clay
12 citiesFort Worth
Tarrant Co · Clay over limestone; SE Fort Worth Blackland runs worse
Arlington
Tarrant Co · Eagle Ford band; sandier west side
Grand Prairie
Dallas/Tarrant Co · Eagle Ford residual clays; sandier west
Carrollton
Dallas/Denton Co · Blackland east, sandy Woodbine west
Highland Park
Dallas Co · Clay over Austin Chalk
University Park
Dallas Co · Clay over Austin Chalk
DeSoto
Dallas Co · Chalk and Eagle Ford transition
Cedar Hill
Dallas/Ellis Co · Chalk escarpment; Eagle Ford clays
Duncanville
Dallas Co · Chalk and Eagle Ford transition
Mansfield
Tarrant/Johnson Co · Eagle Ford band and limestone soils
Burleson
Johnson/Tarrant Co · Clay over limestone; Blackland edge east
Midlothian
Ellis Co · Blackland with chalk escarpment areas
Grand Prairie Limestone Belt & Transition Zones
11 citiesNorth Richland Hills
Tarrant Co · Clay over limestone; sandy areas
Haltom City
Tarrant Co · Clay over limestone and marl
Watauga
Tarrant Co · Limestone and Cross Timbers transition
Hurst
Tarrant Co · Limestone and Cross Timbers transition
Euless
Tarrant Co · Sandy soils west, clay east
Bedford
Tarrant Co · Sandy soils over clay
Coppell
Dallas Co · Woodbine and Eagle Ford transition; strong lot-to-lot variation
The Colony
Denton Co · Sandy west, clay east near the lake
Little Elm
Denton Co · Sandy soils with clay pockets
Denton
Denton Co · Cross Timbers sands; clay areas east
Cleburne
Johnson Co · Clay over limestone and marl
Eastern Cross Timbers Sands
7 citiesGrapevine
Tarrant Co · Sandy Woodbine soils; clayey subsoils on some lots
Southlake
Tarrant Co · Sandy loams over clay
Colleyville
Tarrant Co · Sandy loams over clay
Keller
Tarrant Co · Sandy loams over clay
Flower Mound
Denton Co · Sandy Woodbine soils
Lewisville
Denton Co · Sandy loams; alluvial clay near the lake
Trophy Club
Denton/Tarrant Co · Sandy loams over clay
Western Cross Timbers
2 citiesWeatherford
Parker Co · Pack sands over sandstone; lowest metro risk, not zero
Azle
Parker/Tarrant Co · Sandy loams over sandstone and clay
The Soil Moves in the Top 10-15 Feet.
Piers Reach Below It.
Seasonal moisture only changes soil volume in the "active zone" near the surface. Below it, the ground stays stable year-round. Structural pier repair transfers your pool's weight to that stable ground, which is why we back it with a lifetime warranty. If your pool is settling, cracking, or losing water in a High or Very High city, that is not bad luck. It is geology, and it is fixable.
What the Data Says About North Texas Soil
Every fact below comes from federal soil data, university geology, or published engineering literature.
The State Soil Is a Warning Label
Houston Black clay, the official Texas state soil, is a classic Vertisol built from expansive smectite clays. It covers roughly 1.5 million acres of the Blackland Prairie, including Dallas, Tarrant, Collin, and Kaufman counties.
Source: USDA NRCS Official Series DescriptionCracks Deeper Than a Pool Wall
In dry conditions, USDA has documented cracks in Houston Black soils extending more than 80 inches deep. That is deeper than most pool walls, which means the soil movement runs beneath the entire shell.
Source: USDA NRCS, Houston Black series documentationThree Times the Code Threshold
Building codes flag a soil as expansive at a Plasticity Index of 15 or higher. Houston Black clay commonly tests at PI 40 to 60, roughly three to four times the threshold engineers design around.
Source: 2021 IBC 1803.5.3; published North Texas PI compilationsCostlier Than Every Storm Combined
Per ASCE and HUD estimates, expansive soils damage about 1 in 4 US homes and cause over $15 billion in damage per year, more in a typical year than earthquakes, floods, hurricanes, and tornadoes combined.
Source: HUD Cityscape (2023); British Geological Survey reviewDocumented Movement of Up to 7 Inches
The Eagle Ford Shale, whose type locality sits in western Dallas County, weathers into bentonite-rich residual clays. Differential swell of up to roughly 7 inches has been documented, enough to crack foundations, roads, and pool shells.
Source: Dallas geological literature; USACE Fort Worth District geotechnical documentationThe Active Zone Is the Whole Story
Seasonal wet-dry cycles change soil volume in roughly the top 10 to 15 feet, the active zone. Below it, moisture and volume stay stable year-round. Structures supported below the active zone stop moving with the seasons.
Source: Published Texas geotechnical guidance on expansive claysHow We Built This Map
Ratings reflect the dominant soils and geologic formations under each city's residential areas, normalized to five classes from USDA shrink-swell (linear extensibility) classifications and published North Texas geology. Cities spanning multiple soil zones are rated by their dominant residential zone, with variation noted. Soil conditions vary lot to lot; a city rating describes geologic risk, not the condition of any individual property.
Primary Data
USDA NRCS soil survey data, including the Official Series Descriptions and the Web Soil Survey (SSURGO), which classifies shrink-swell behavior for every mapped soil in the metroplex. Anyone can verify a specific property at the USDA Web Soil Survey.
Source: USDA Web Soil SurveyGeology & Engineering Literature
Regional formation mapping and expansiveness documentation from published Dallas geology, US Army Corps of Engineers geotechnical documentation for Dallas County, Baylor geological studies on the Taylor Marl, and Texas Parks & Wildlife ecoregion soil descriptions.
Sources: Environmental & Engineering Geoscience; USACE Fort Worth District; Baylor Geological Studies; TPWDDFW Soil Risk FAQ
Straight answers about expansive soil and what it means for your pool.
What makes a soil "expansive"?
Which DFW cities have the worst soil for pools?
Which DFW areas have the most stable soil?
My city is rated Very High. Does that mean my pool will crack?
Can anything be done about soil movement under an existing pool?
How can I check the soil on my specific property?
Think the Soil Is Moving Your Pool?
Get a structural diagnosis with a same-day written report. If piers are the answer, the repair is backed for life.
Last reviewed: Septmeber 2026