Rapid City, South Dakota: what the ground under the city is like
Rapid City sits in Pennington County, on missouri plateau (unglaciated great plains). The soil mapped here is predominantly classified well drained — and that classification, not the rainfall total, is what decides how a basement behaves.
25% of the mapped soil area around Rapid City is wet enough that the USDA describes it as needing artificial drainage.
Linear extensibility 9.8% — very high.
Shallowest annual water table around 190 cm (6.2 ft).
Values are for Pennington County, which is what the soil survey resolves to. Full county report · soil map for a specific address.
The ground under Rapid City
Missouri Plateau (unglaciated Great Plains). Weathered clay shales and sandstones, Pierre Shale and equivalents
The water table is deep, so basements rarely flood — but Pierre Shale is one of the most expansive substrates in North America. The risk here is mechanical, not hydraulic.
When it shows up here
| Water | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Ground movement | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
The mechanism here is the wet–dry cycle, and it peaks in the summer drought: clay shrinks hard from June to September, then the first heavy rain swells it back. Foundation cracks tend to appear at the ends of that swing, not during it.
Climate pattern for this physiographic region, not a forecast for your house and not from the soil survey. It answers a question homeowners actually ask: when does this show up.
What repairs cost in South Dakota
| Reference job | Modelled range |
|---|---|
| Interior drain along two walls + sump pump | $4,750–$10,200 |
| Exterior excavation of one 40 ft wall | $3,550–$10,150 |
| Underpinning on 10 piers | $14,100–$30,100 |
Regional factor for SD: ×0.94. Full cost breakdown for South Dakota · run your own dimensions.
ZIP codes in Rapid City
57701, 57702, 57703, 57709
Soil does not stop at a city boundary, and neither does this data — every ZIP code above resolves to the same county soil survey. For the individual survey polygons around one address, use the soil map.
Questions about Rapid City
Is the soil the same everywhere in Rapid City?
No. These values describe Pennington County as a whole, which is the unit the soil survey publishes. Within a city, map units change over a few hundred metres — the soil map draws the actual polygons around a point and is the honest answer for one address.
Which contractor should I call in Rapid City?
We do not rank or recommend individual firms and we are not one. What this page is for is knowing which kind of work the ground here points to before anyone quotes you, and which claim to check. If you want quotes, the form below passes your request to the named networks.
Does this replace an inspection?
No. It tells you what the ground is; an inspection tells you what your building is doing on it. The useful order is: read this, print the brief for your county, then have someone look.
Get quotes in Rapid City
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Page data updated