Denton County Soil and Rock: Which Band Is Your House On?

Here are all 33 towns, sorted by band. The first figure is the share of each town's land points on soil rated high or very high. Then comes very high alone. Points that fell on water are left out.

West band

• Krum 96%, 48% very high
• Sanger 84%, 28% very high
• Ponder 76%, 52% very high
• Northlake 76%, 32% very high
• Justin 68%, 28% very high
• Roanoke 64%, 20% very high
• Argyle 44%, 12% very high

Middle band

• Paloma Creek 56.5%, 26.1% very high
• Oak Point 40%, 6.7% very high
• Providence Village 34.8%, 8.7% very high
• Trophy Club 28.6%, 9.5% very high
• Pilot Point 28.6%, 4.8% very high
• Cross Roads 25%, 5% very high
• Lake Dallas 25%, 6.2% very high
• Krugerville 20%, 4% very high
• Copper Canyon 16.7%, none very high
• Highland Village 16.7%, none very high
• Hickory Creek 16.7%, 5.6% very high
• Aubrey 16%, 4% very high
• Flower Mound 13.6%, none very high
• Double Oak 12.5%, none very high
• Lantana 12%, none very high
• Bartonville 8%, 4% very high
• Shady Shores 5.3%, none very high
• Corinth 4.8%, none very high

East band

• The Colony 94.7%, 84.2% very high
• Savannah 87.5%, 25% very high
• Little Elm 85.7%, 52.4% very high
• Frisco 84%, 84% very high
• Prosper 84%, 76% very high
• Paloma Creek South 78.3%, 47.8% very high

Outside the three bands

• Denton 44%, 12% very high (on the edge of the west and middle bands)
• Lewisville 80%, 25% very high (mostly river deposits)

The pattern holds across all 33 towns. Every west town but Argyle, which sits half on the Woodbine, comes in at 64% or more. Every east town comes in at 78.3% or more. In the middle, 10 of the 18 towns are under 20%, and 7 have no very high point at all. Paloma Creek, the middle town with the most, sits beside the east band.

Krum, Sanger, Ponder, Northlake and Justin have 60% to 100% of their points on the Grand Prairie's rock. Roanoke and Argyle have a little under half. TPWD describes the wider Fort Worth Prairie as "thin soil over hard layers of resistant limestone." Near Denton, the soil survey mostly shows something else: deep clay, with no rock in the top 80 inches.

• Sanger clay is the most common soil in Krum, at 10 of 25 points. In its usual form, it reads 8.4 at the surface and 9.1 from about 7 inches down to about 3 feet. It's 45% to 48% clay, with no rock in the 80 inches the survey describes.
• Ponder loam reads 4.5 in its top 6 or 7 inches, then 7.5 all the way down to 70 inches or more. It formed from the shale of the Grayson Marl.
• Slidell clay, at 6 of Ponder's 25 points, is half clay from top to bottom. It reads 10 in its top 32 inches and stays at 9 to about 49 inches down.

Rock does come close in places, and that's where TPWD's line fits. Three soils here formed over limestone and sit on hard bedrock: Aledo gravelly clay loam at about 12 inches, Somervell gravelly loam at about 27 and Mingo clay loam at about 29 to 31. Together they cover 23 of the west band's 175 land points, about 1 in 8. Justin has the most, at 8 of its 25.

Eighteen of the towns are in the middle band, with 44% to 96% of their points on the Woodbine. Among them are Corinth, Lantana, Highland Village, Flower Mound and Trophy Club. The soils here look sandy in a flower bed. Most of them change a few inches down.

• Birome fine sandy loam is the most common soil in 9 of the 18 towns. It has about 6 to 8 inches of sandy loam, then a layer that's 45% clay and reads 4.5. Soft bedrock sits about 27 to 34 inches down.
• Callisburg fine sandy loam has about 5 inches of sandy loam over sandy clay that's 40% clay. It reads 4.5 all the way to 80 inches, with no rock.
• Gasil fine sandy loam is sandier. Its sandy top runs 13 to 17 inches deep, and the sandy clay loam below reads just 1.8.
• Silstid loamy fine sand is the true sand. It's loamy sand for about 6 feet, only 7.5% clay, and in Denton County's survey it reads 1.5 all the way down.

So "sandy" isn't the same as "no clay." A reading of 4.5 is moderate, and that's enough for the USDA's warning about damage to buildings. It's still well below the 9 to 17 that the clay bands reach.

Where do the middle band's higher readings come from, then? Mostly from small patches of two soils, Wilson and Navo clay loam, which read 7.5. They make up 41 of its 63 high points.

Very high points are rarer, 18 in all, and 6 of those are in Paloma Creek. Most are the east band's black clays turning up in the middle. A few sit on low ground, on soils whose survey names include "flooded."

The Colony, Savannah, Little Elm, Frisco, Prosper and Paloma Creek South have 44% to 100% of their points on the Eagle Ford's black shale or the Austin Chalk. This band has the most very high soil: 84 of its 137 land points.

• Houston Black clay covers about half of our Frisco and Prosper points, at 12 and 13 of 25. At 24 of those 26 points, the reading holds at 12 from top to bottom of the 80 inches, and the survey finds no rock. It's 54% clay.
• Ferris clay formed in the shale of the Eagle Ford. It reads 17 from the surface to about 43 inches, where it meets dense bedrock. It's the most common soil in The Colony, tied with Branyon at 6 of 19 land points.
• Branyon clay is river-laid clay, carried down long ago from mudstone. It reads 9.9 in its top foot, then 13 down to 80 inches. It's the most common soil in Little Elm, at 7 of 21 land points.
• Heiden clay reads about 12 down to about 58 inches, where the survey finds dense material. It covers 6 of Frisco's 25 points.

One east-band soil breaks the pattern. Stephen silty clay formed on chalk. It reads 4.5 in its top 9 inches and 1.2 below that, with soft bedrock about 15 inches down. It turned up at 4 of Prosper's points and 3 of Frisco's. So even in the east band, some of the ground is a thin soil over chalk.

Most of our Lewisville land points, 12 of 20, landed on river deposits, not on any of the three bands. That doesn't make the ground sandy. Of its 20 land points, 16 came up high or very high, and 5 very high.

The soils there are a mix, with no single one in charge. Several have names that end "frequently flooded" or "occasionally flooded," such as Frio and Ovan. Ovan clay is close to half clay and reads 7.5 from the surface down to 5 feet or more. A few points landed on the east band's Ferris and Branyon clays too.

Of our 25 Denton points, 48% landed on Grand Prairie rock and 40% on the Woodbine. On the map, the Woodbine lies under the middle of town and spreads to the south and east. The marl and the Denton Clay lie to the west and north. You may hear that Denton's sand lies west of I-35. The map says otherwise.

We checked the rock 1 kilometer either side of I-35, I-35E and I-35W, at steps north and south of Denton. On the west side of Denton, the map shows Grand Prairie rock on both sides of the highway. South-east of the split, I-35E runs on the Woodbine toward Lewisville. The highway isn't the line between sand and clay.

The soil is mixed too. In Denton, 11 of our 25 points came up high or very high, 3 of them very high on Sanger clay. The two most common soils, Callisburg and Justin, are sandy loams over a moderate layer.

The Denton Clay takes its name from Denton Creek, the US Geological Survey's record of rock names says. The Corps of Engineers dammed the same creek to make Grapevine Lake.

You can find the soil names for your own lot in a few minutes, free, in the USDA's Web Soil Survey.

1. On the Web Soil Survey home page, the button to press says "Start Web Soil Survey."
2. In the "Quick Navigation" panel on the left, choose "Address." Enter yours, then click "View."
3. Pick a drawing tool from the bar over the map, the rectangle or the polygon, and outline your lot with it.
4. Click the "Soil Map" tab. It lists each soil inside the area you drew.
5. Match the names to this page. Sanger, Ponder and Slidell are west-band clays. Birome, Callisburg, Gasil and Silstid are the middle band's sandy soils. Houston Black, Ferris, Branyon and Heiden are the east band's black clays.

Denton County has its own survey. Near the county lines, your lot may fall in Collin County's or Tarrant County's instead. The USDA itself says some engineering uses need a check on site, so treat the map as a starting point.

On the west and east bands, the soil itself is the first suspect. NOAA's Denton 2 SE station averages its most rain in May, at 4.86 inches, and October, at 4.64. July and August average highs near 96°F. Clay that dries through a hot summer and wets again in the fall can open a crack and close it again.

On the middle band, the soil moves less, so look hard at water. A leak, a downspout that drains at the wall or a yard that slopes toward the house can all soak one side. The Texas Section of the American Society of Civil Engineers calls for ground that falls at least 6 inches in the first 10 feet from the house. It also favors soil moisture that stays near even on every side.

On every band, one set of floor readings is only a snapshot. The same guidelines say repeated readings, taken months apart, are what show a change. Keep a copy of any readings an inspector takes.

On the clay bands, clay can push a house up as well as let it drop. A paper from the Foundation Performance Association, a Houston group of engineers and repair firms writing for southeast Texas, warns that piers won't stop that upward push unless they're designed to. Its repair guidelines add that warranties don't usually cover upward movement unless the contract says so. That's worth asking about before you sign. A free foundation inspection is a good place to start.