Hill Country Rock vs. Blackland Clay: Soils Under New Braunfels, Seguin and Canyon Lake

We mapped USDA soil data for nine spots from Canyon Lake to Seguin. Here's what's under each, and what it means for a foundation.

Get a price from a local pro

Free to use
One local company, not a list
No obligation to hire

Referral website, not the contractor. How it works

Around New Braunfels, the ground under a house is either shallow soil over Hill Country limestone or deep Blackland and river-terrace clay that swells and shrinks. USDA soil data shows the line falls right through town.

New Braunfels Foundation Co. is a referral website, not a foundation repair company. We send your request to one independent local foundation repair company. You never pay us; companies we refer you to may pay us for referrals.

This page is a reference, not a sales page. We pulled USDA's soil survey for nine sample spots, from the Canyon Lake shoreline to downtown Seguin, and summarized what each one means for a slab or pier-and-beam house.

The short version, by area

Each row is a box about 3 km north to south and 2.6 km east to west (under 2 miles each way), centered on the point listed. Percentages are shares of land area (lake water excluded) in USDA's mapped soils.

Sample area	Most common mapped soils	Land rated high or very high shrink-swell	Land with rock within 20 in. of the surface
Canyon Lake, CDP interior point (Census)	Brackett, rock outcrop, Eckrant, Comfort	3%	95%
Canyon Lake, north shore (Tye Preston library area)	Brackett, rock outcrop, Real, Boerne	9%	65%
West New Braunfels, about 3 mi west of Main Plaza	Rumple, Comfort, Tarpley	5%	45%
Gruene (Gruene Hall)	Branyon, Comfort, Krum, Lewisville	46%	26%
Downtown New Braunfels (Main Plaza)	Krum, Lewisville, Oakalla, Houston Black	56%	6%
East New Braunfels, Guadalupe County side, about 3 mi east	Branyon, Barbarosa, Queeny, Sunev	69%	0%
McQueeney	Lewisville, Sunev, Branyon, Tinn	67%	0%
Seguin (City Hall)	Barbarosa, Queeny, Branyon, Sunev	60%	0%
Seguin, west (Texas Lutheran University)	Barbarosa, Branyon, Sunev, Queeny	74%	0%

Data: USDA NRCS soil survey (SSURGO) via Soil Data Access, queried October 24, 2026. See "How we counted" below.

Read down the table and you're walking off the Edwards Plateau and onto the coastal plain. The Texas State Historical Association places Comal County "on the divide between the Blackland Prairies and the Balcones Escarpment," the fault zone that separates the two. Gruene, with clay terraces and rocky ridges in the same box, sits close to that seam.

What "shrink-swell" means here

USDA rates each soil layer by linear extensibility, the percent a clod shrinks from moist to oven-dry. NRCS groups it into four classes: low (under 3 percent), moderate (3 to 6), high (6 to 9) and very high (9 or more). Our table counts a soil as "high or very high" if any layer reaches 6 percent.

For a foundation, high shrink-swell means the soil's volume changes a lot between a drought and a wet spell. A slab edge that dries out drops; the same edge can rise after heavy rain. Movement is rarely even across a house, and that unevenness is what cracks brick and racks door frames.

The clay side: Branyon, Barbarosa, Krum, Lewisville

These are the soils behind most of the "high" numbers in the table.

Soil	Where it showed up	What USDA says
Branyon	Gruene, east New Braunfels, McQueeney, Seguin	40 to 60 percent clay; dry-season cracks 1 to 3 in. wide reaching 20 in. or deeper, open 90 to 150 days in most years. Highest rating in our sample (linear extensibility up to 13).
Barbarosa	East New Braunfels, Seguin	A deep clay soil on ancient stream terraces, first described in Guadalupe County in 1973 and formerly lumped in with Krum.
Krum	Downtown New Braunfels, Gruene	Very deep clay formed in alluvium from chalk and marl, on stream terraces. Rated high to very high.
Lewisville	Downtown, McQueeney	Very deep, along major streams in the Blackland and Grand prairies. Rated high.

Houston Black, the Blackland clay most Texans know, appeared too, but only in small patches in our downtown and McQueeney boxes.

What it means for a house on these soils:

Expect seasonal movement. A crack that opens in August and closes in a wet spring is typical behavior for these clays, not proof of failure.
Moisture next to the slab matters. Steady watering at the edge, gutters that discharge away from the house, and soil graded away from the foundation all reduce the swing.
Pier depth is a real question. Ask a company how deep it expects piers to go to get below the zone that dries and rewets, and how it decided.

A New Braunfels building official told Community Impact in 2023 that homes with highly expansive clay "immediately under your foundation" have "a much higher chance of having foundation problems." Our table is a way to see where that clay is mapped.

The rock side: Rumple, Comfort, Brackett

West of the escarpment and around Canyon Lake, the soil is thin.

Soil	Where it showed up	What USDA says
Rumple	West New Braunfels	Moderately deep over limestone: hard rock at 20 to 40 in. Very gravelly.
Comfort	West New Braunfels, Gruene, Canyon Lake	Shallow to hard limestone at 10 to 20 in., but the thin soil above it is 40 to 60 percent clay. USDA notes it's used for "rural homesites."
Brackett	Canyon Lake	Shallow to soft limestone of the Glen Rose formation, at 5 to 20 in. Slopes up to 60 percent.

What it means for a house on these soils:

Less seasonal heave, but not zero. A thin layer of clay over rock can still shrink and swell, and Comfort's clay content is high.
Uneven support is the bigger risk. On a hillside lot, part of a house may sit on cut rock and part on fill. Fill can settle, and the two halves of the house then move differently.
Water finds the rock. Runoff tends to travel along the top of shallow limestone, so check where water goes in a hard rain and keep it from collecting against the foundation.
Pier plans look different. Where rock is close to the surface, ask the company how it will anchor or bear on it, and whether the plan changes from one side of the house to the other.

Look up your own lot

Soil can change within one block, so the table is a starting point. To see what's mapped under your house:

Open USDA's free Web Soil Survey and choose "Start WSS."
Type your address in the Area of Interest search box, zoom in, and draw a box around your lot.
Open the Soil Map tab to see the map unit names (for example, "Branyon clay" or "Comfort-Rock outcrop complex").
Under Soil Data Explorer, open Soil Properties and Qualities. Linear extensibility is under Soil Physical Properties, and depth to a restrictive layer is under Soil Qualities and Features.

If you're buying a house or weighing a large bid, an independent Texas-licensed professional engineer (P.E.) can tell you whether a soil report is worth ordering. Our foundation inspection guide explains the difference between a company's evaluation and an engineer's report, and the signs of foundation problems guide covers what to watch for on either kind of ground.

How we counted

Where: nine points. Four are addresses geocoded with the Census Bureau's geocoder (199 Main Plaza and 1281 Gruene Rd. in New Braunfels, 205 N. River St. and 1000 W. Court St. in Seguin, and 16311 S. Access Rd. at Canyon Lake). Two are Census interior points for the Canyon Lake and McQueeney CDPs. Two are points about 3 miles west and east of Main Plaza; the Census geocoder places both inside New Braunfels city limits, the eastern one in Guadalupe County.
Area: a box 0.027 degrees of latitude by 0.027 degrees of longitude around each point (about 3 km by 2.6 km).
Data: for each box we asked USDA's Soil Data Access service for the mapped soil polygons, their area, each map unit's component soils and percentages, the highest linear extensibility in any layer, and the shallowest bedrock contact.
Shares: each component's share is map-unit area times its component percentage, divided by land area. A soil counts as "high or very high shrink-swell" at 6 percent or more. "Rock within 20 in." counts soils with bedrock (hard or soft) at 51 cm or less, plus rock outcrop.
Limits: soil surveys map patterns at a scale meant for land planning, not individual building sites. Fill placed during construction isn't mapped. A survey can't tell you how your house will perform, and the soil type alone doesn't mean a foundation will or won't move. Use it to ask better questions.

Updated October 24, 2026.

Foundation repair in Canyon Lake, on hillside lots and county rules
Foundation repair in Seguin, on Guadalupe County clay and city permits
Slab foundation repair and pier and beam foundation repair
The foundation repair cost guide

Common questions

Is New Braunfels on clay or rock?

Both. In our USDA soil sample, the box of about 3 km around Main Plaza was 56 percent soils rated high or very high for shrink-swell, while a box about 3 miles west of Main Plaza was 5 percent, with shallow limestone under nearly half of it. Which one you have depends on which side of the Balcones Escarpment your lot sits.

Are Hill Country homes safe from foundation problems?

No. Shallow rock moves less with the seasons than Blackland clay, but USDA rates some rocky soils, such as Comfort, as having 40 to 60 percent clay in the thin layer above the limestone. Slopes, fill pads and drainage can also leave part of a house poorly supported. The risk is different, not absent.

Does Seguin have the same soil as New Braunfels?

Seguin's soils in our sample were mostly Barbarosa, Queeny and Branyon, all on old stream terraces. Barbarosa and Branyon are rated high or very high for shrink-swell, so Seguin's clay risk looks more like east New Braunfels than like the Hill Country side.

How do I find the soil under my own house?

Open USDA's free Web Soil Survey, zoom to your address, draw an area of interest around your lot, then open the Soil Data Explorer tab and look up linear extensibility (shrink-swell) and depth to bedrock. The map is a guide, not a test of the ground under your slab. For a repair decision, an independent Texas-licensed professional engineer (P.E.) can order a geotechnical report.

Sources (15)

Last updated 2026-10-24