SinkholeOdds

Sinkhole risk in Alfalfa County, OK: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock
11%
At or near the surface
11%
Buried under cover
0%

What to do about a house in Alfalfa County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 99 of Alfalfa County's 867 square miles on soluble rock, 99 of them with the rock at or near the surface. With about 5,712 residents (7 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 396 map points about 1.5 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Alfalfa County

The nearest county rated sinkhole country is Woods County, OK, about 30 miles west, close enough that the same rock may run under the county line. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

The rock underneath

The largest mapped soluble unit here is the Salt Plains Formation (shale), Early Permian in age, covering about 6% of the county. Next is the Flowerpot Shale at 6%.

11% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

The county also lies over the Permian Basin, Anadarko Basin,Dalhart Basin, Palo Duro Basin, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Oklahoma

Alfalfa County ranks 42 of 77 in Oklahoma for soluble rock at the surface, and sits above 69% of US counties on that measure.