Vertisols: Clay Soils That Shrink, Swell and Crack

Vertisols are the clay soils that move: they shrink and crack as they dry and swell shut when they wet.^[1] Below: the three tests that make a soil a Vertisol, what the cracks do to the soil and to anything built on it, the suborders, and where USDA’s survey maps them.

Is your soil a Vertisol?

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Vertisols are clayey soils high in expanding clay minerals that shrink as they dry and swell as they wet, opening deep, wide cracks for part of the year. To qualify, a soil needs at least 30% clay in every horizon to about 20 inches (50 cm). USDA maps about 42.2 million acres in the US, most in Texas.

What makes a soil a Vertisol

NRCS starts with the clay: Vertisols have a high content of expanding clay minerals, and they change volume sharply with moisture, shrinking as they dry and swelling as they get wetter. They’re clayey soils with deep, wide cracks for some time during the year.^[1]

They form where the parent material allows expansive clay minerals to develop. The name comes from the Latin verto, to turn, and they cover about 2% of the world’s glacier-free land.^[2]

The three tests: clay, slickensides, cracks

The University of Idaho lists what a Vertisol has:

a layer at least about 10 inches (25 cm) thick with slickensides or wedge-shaped peds whose long axes are tilted;
at least 30% clay in all horizons to a depth of about 20 inches (50 cm);
cracks that open and close periodically.^[3]

In horizon names the suffix ss marks pedogenic slickensides, as in Bss.^[4]

A Vertisol in A–B, the survey’s most common Vertisol sequence: clayey from the top, with cracks that open from the surface as it dries and slickensides, the ss in Bss, in the subsoil. Not to scale.^[3][4][5]

The clay rule shows in the survey: the first mineral layer is clay (67.8%), silty clay (17.4%) and silty clay loam (6.5%), so clay and silty clay together cover 85.2% of Vertisol acres. More on those classes on the clay and silty clay pages.^[5]

Why Vertisols crack

Dry, Vertisols open cracks that can be more than three feet (one meter) deep and several inches, or centimeters, wide.^[2]

Dry, a Vertisol opens cracks that can run more than three feet (one meter) deep. Wet, its clay swells, the cracks close and water tends to pool on the surface.^[2][3]

The cracks churn the soil. Surface material falls into them and is worked into the lower horizons once the soil is wet again, and this shrink-swell action generally keeps distinct, well-developed horizons from forming.^[6][3]

Water moves through them slowly. The median saturated hydraulic conductivity (Ksat) is 0.22 µm/s, moderately low and the slowest of any order, and 86.8% of the acres are in hydrologic soil group D, where water soaks in slowly, the largest share of any order.^[5][8][9]

Vertisols, foundations and roads

Vertisols are well known among engineers because their unique properties limit engineering uses, NRCS notes, and the University of Idaho says their shrink-swell action creates serious engineering problems. In its Xererts description NRCS adds that because those soils become dry every summer and moisten in winter, the damage to structures and roads is very significant.^[1][3]

The Soil Science Society of America adds that the movement of these soils can crack building foundations and buckle roads.^[2]

For an address, the expansive soil checker shows the shrink-swell rating USDA maps there, and the building site checker gives USDA’s ratings for dwellings and roads.

Vertisol suborders

Aquerts, the wet Vertisols, mostly in Texas, the lower Mississippi River Valley and the valley of the Red River of the North.
Torrerts, the Vertisols of arid climates, in western Texas and in Arizona and New Mexico.
Usterts, mostly in Texas, South Dakota and Montana.
Xererts, the Vertisols of Mediterranean climates, mostly in California, Oregon and Idaho.
Uderts, the Vertisols of humid areas.^[1]

A sixth, Cryerts, is not known to occur in the United States.^[1] The survey data doesn’t record suborders, so there are no acres for them here.

Farming on Vertisols

Most Vertisols are well suited to mechanized farming if there is plenty of rainfall or irrigation water, NRCS says; their natural vegetation is mostly grass, savanna, open forest or desert shrub.^[1]

The Soil Science Society of America calls them highly fertile thanks to their clay, with one catch: water tends to pool on the surface when they’re wet.^[2]

Another 12.5% is prime if drained, protected or irrigated. 69.8% of rated acres are in the cultivable capability Classes I–IV, and erosion (e) and excess water (w) tie as the most common hazard, at 38.2% each.^[5][10][11]

Farmland class	Share of Vertisol acres
Prime farmland	32.2%
Prime if drained, protected or irrigated	12.5%
Statewide or local importance	7.6%
Not prime	47.7%

What Vertisols are like in the survey

95.9% of described Vertisol acres have a B horizon, and the two most common sequences are A–B (17.2 million acres) and A–B–C (13.4 million acres). Where a parent material is recorded it’s most often alluvium (56.9%), residuum (23.5%) and marine (10.4%).^[5]

Property	Median (middle half)	Components
Water held (in per ft)	1.8 (1.4–1.9)	13,809
Ksat (µm/s)	0.2 (0.2–0.9) · Moderately low	13,809
Bulk density (g/cm³)	1.30 (1.22–1.35)	13,809
pH	7.3 (6.8–7.9) · neutral	13,809
Organic matter (%)	2.3 (2.0–3.0)	13,809

Drainage splits: 62.2% of the acres are well or moderately well drained and 28.3% poorly or very poorly drained. The median surface pH is 7.3.^[5][12][13]

Drainage class	Share of Vertisol acres	Million acres
Somewhat excessively drained	0.0%	0.0
Well drained	37.3%	15.7
Moderately well drained	24.9%	10.5
Somewhat poorly drained	9.5%	4.0
Poorly drained	27.5%	11.6
Very poorly drained	0.9%	0.4

Where Vertisols are in the US

Top 10 states by Vertisol acres (USDA survey).

Texas has the most Vertisol acres by far, 15.6 million, or 37.0% of the order. They aren’t the leading order in any state; as a share of a state’s own soil acres they peak in Louisiana, at 13.6%.^[5]

State	Share of the state’s soil acres	Million acres
Louisiana	13.6%	3.5
Texas	10.1%	15.6
South Dakota	8.8%	4.2
Mississippi	8.2%	2.3
Arkansas	6.5%	2.0
North Dakota	3.4%	1.5
California	3.4%	2.8
Montana	3.2%	2.8

Most widespread Vertisol series

Series	Acres	Most in	Survey areas
Sharkey	3,610,614	Louisiana	65
Houston Black	1,411,597	Texas	32
Heiden	1,099,293	Texas	42
Alligator	1,037,844	Mississippi	46
Opal	1,002,661	South Dakota	22
Fargo	976,808	North Dakota	39
Promise	783,096	South Dakota	27
Victoria	723,628	Texas	5

Sharkey (Louisiana), Houston Black (Texas) and Heiden (Texas) cover the most ground; each links to its official USDA description.^[5][14]

Download the Vertisols data (CSV)

Vertisols compared with other orders

Vertisols rank tenth of the twelve orders by US acres but first by prime-farmland share.^[5][10]

Order	Share	Median A	Surface pH	Prime farmland
Alfisols	14.9%	7.1 in	6.2	20.6%
Andisols	1.6%	8.3 in	5.8	1.8%
Aridisols	8.7%	3.5 in	7.9	0.1%
Entisols	12.5%	5.1 in	7.4	3.0%
Gelisols	6.3%	3.9 in	5.3	0.0%
Histosols	2.4%	—	—	0.0%
Inceptisols	13.8%	5.1 in	5.6	5.3%
Mollisols	23.6%	9.8 in	7.0	23.2%
Oxisols	0.0%	5.9 in	5.1	20.7%
Spodosols	4.5%	3.9 in	4.8	2.2%
Ultisols	9.6%	5.9 in	5.3	24.0%
Vertisols	2.1%	7.1 in	7.3	32.2%

Histosols show a dash: their surface is organic material (peat or muck), so a topsoil (A) or surface pH median would describe mineral soil beneath it.

Frequently asked questions

What are Vertisols?: Clayey soils high in expanding clay minerals that shrink when they dry and swell when they wet, with deep, wide cracks for part of the year.^[1]
How much clay does a Vertisol have?: At least 30% clay in all horizons to a depth of about 20 inches (50 cm), along with slickensides or wedge-shaped peds and cracks that open and close.^[3]
Why do Vertisols crack?: Their expanding clay shrinks as it dries, opening cracks that can be more than three feet (one meter) deep; it swells again when wet.^[1][2]
What do slickensides have to do with Vertisols?: They’re part of one of the order’s tests: a layer at least about 10 inches (25 cm) thick with slickensides or wedge-shaped peds whose long axes are tilted. In horizon names, the suffix ss marks pedogenic slickensides.^[3][4]
Are Vertisols bad for foundations?: Their movement can crack foundations and buckle roads, and their shrink-swell creates serious engineering problems. Check an address with the expansive soil checker.^[2][3]
Are Vertisols good for farming?: Often yes: most suit mechanized farming given plenty of rain or irrigation, and 32.2% of their acres are prime farmland.^[1][5][10]
Where are Vertisols found in the US?: Texas has 37.0% of the acres, and the share of a state’s soil peaks in Louisiana at 13.6%.^[5]
What does ‘Vertisol’ mean?: It comes from the Latin verto, to turn.^[2]

How we calculate this

Acres come from USDA SSURGO via Soil Data Access, weighted by each soil component's share of its map unit (USDA's representative percent) and summed across 3,386 detailed USDA soil surveys; shares are of the US acres that have a recorded order. Surface medians (pH, organic matter, water held, Ksat and bulk density) are of each component's first mineral layer below any organic (O) layer. Topsoil thickness, horizon sequences, farmland class and parent material come from a matching read of one profile per soil component. Data generated 2026-10-07.

Drainage class, hydrologic soil group, pH class, land capability, shrink-swell and in-state shares come from our soil-order profile aggregation of the same surveys (data generated 2026-10-30); in-state shares rank the 50 states and DC with at least 1,000,000 acres that have an order.

Shrink-swell classes follow USDA’s linear-extensibility bands: low under 3%, moderate 3 to 6%, high 6 to 9% and very high 9% or more.

More in our methodology.

Sources

Marko Visic · MPharm, BSc Physics · Last reviewed November 13, 2026