MARION, Ill. (AP) — Authorities in southern Illinois were investigating after skeletal remains were found at a wildlife refuge.

The Williamson County Sheriff’s Office was working with the U.S. Fish and Wildlife Service, Illinois State Police and the county coroner.

The remains were found Thursday at the Crab Orchard National Wildlife Refuge, according to a news release. No further details were released.

The roughly 44,000-acre refuge includes hardwood and pine forests, croplands, grasslands rolling hills and several lakes.