MARION COUNTY, Iowa (WHO) — A road in rural Marion County, Iowa is shut down as officials investigate a giant sinkhole that’s opening in the ground. The hole is approximately 20-feet deep and 30-feet in diameter.

It sits in the 1700 block of 135th Place, a rural gravel road. The hole is opening just east of the roadway. Marion County Road’s Department closed the road in the area on Wednesday evening.

According to a news release, officials still haven’t identified the cause of the sinkhole. It sits in an area where numerous coal mines were dug a century ago. An interactive online map of former mine sites in the state shows there was a 17-acre mine near where the sinkhole is opening. Marion and other south-central Iowa counties have some of the densest populations of former mines in Iowa.