What are foundation conditions like in Duncan, Oklahoma?

Reviewed by Preston · Updated 2026-11-12

In short: About 26% of Duncan is mapped in soils rated high shrink-swell and 20% moderate ¹. The soil survey also maps bedrock within 40 inches under about 38% ¹. Which of these a house sits on decides whether clay swell, water, rock or soft ground is the thing to watch.

What does the soil survey show for Duncan?

Duncan covers about 43 square miles ² and had 22,692 people in the 2020 Census ².

Which soils matter most for houses in Duncan?

• Stephenville, about 18% of the area ¹: Moderately deep, well drained, soils formed in material weathered from sandstone of Permian age ³.
• Zaneis, about 13% of the area ¹: Deep, well drained soils that formed in material weathered from interbedded sandstone and shale of Permian age ⁴.
• Port, about 6% of the area ¹: Very deep, well drained, moderately permeable flood plain soils that formed in calcareous loamy alluvium of Recent age ⁵.
• Chickasha, about 6% of the area ¹: Deep, well drained, moderately permeable soils that formed in material weathered from sandstone of Permian age ⁶.
• Newalla, about 5% of the area ¹: Deep, moderately well drained, very slowly permeable soils ⁷.
• Kirkland, about 12%, is land the survey does not rate as soil ¹.
• Water, about 11%, is open water ¹.

What does this mean for houses in Duncan?

Clay that swells and shrinks. Where high shrink-swell soil sits under a house, wet spells lift the slab edges and drought drops them, and uneven watering does more harm than uniform change. See perimeter wetting heave, edge drop in drought and tree-root drying.

Shallow rock. Where bedrock is close to the surface, lots are often cut into rock on one side and built up with fill on the other, so fill settlement and slope creep matter more than clay swell, and piers can stop at very different depths across one house. See depth to rock from borings.

Which soils cover Duncan?

Looking for a foundation company near Duncan?

Companies that serve Duncan can appear on the company map in the Homeowner Hub. Paid listings there are marked Sponsored; the library and the AI guide don't rank or recommend any of them.

Buying or selling a house in Duncan? Realtors who serve the area can be on the same map, also marked Sponsored, and for realtors covers the seller disclosure form, inspections and the sale timeline. Seeing cracks at home? Start with for homeowners.

How were these numbers measured?

We overlaid the city limits from the Census Bureau ² on the USDA soil survey's map units ¹ and added up the area of each soil. Where a map unit is a mix of soils, its area was split by the percentages the survey lists for its major soils, so shares leave out minor inclusions and do not add to 100%. Shrink-swell is rated by the linear extensibility of a soil's most expansive layer, the survey's measure of how much it changes length between wet and dry (6% or more is high). Water table, bedrock and flooding come from the survey's map-unit summaries: the shallowest water table in any month, the shallowest bedrock, and the most common flooding frequency. Bedrock here includes soft, weathered sandstone and shale that a pier can push through, so it is not the depth where piers stop. These are mapped averages, not a test of any one lot; fill, grading and the soil actually under a house can differ, which is why a site visit or soil boring still decides a repair.

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