The Friars Hole Cave is the longest cave in West Virginia, with eight entrances and 44 miles of surveyed passage. The cave is located on the western flank of Droop Mountain in Pocahontas and Greenbrier counties. The cave lies mostly in middle Greenbrier Group limestones (Mississippian Age). Saltpeter was mined in the cave near the Snedegar entrance during the Civil War. All of the entrances of this non-commercial cave are privately owned and several are on lands that are part of the Friars Hole Cave Preserve, which was started by Gordon Mothes in 1976. A photograph by Huntley Ingalls of the vertical pit entrance called the Crookshank Hole appeared in the June 1964 issue of National Geographic. Throughout the 1960s, various cavers explored and surveyed from the different entrances, and it was ascertained in 1976 that Friars Hole Cave at the southern end connected with Snedegars Cave at the northern end. With nearly 45 miles mapped, Friars Hole Cave is the seventh-longest cave in the U.S. and the 31st-longest cave in the world. Water flowing through the cave includes part of the subterranean flow of Hills Creek. The cave should be entered only with permission of the various landowners. The West Virginia Cave Conservancy advises that the cave is no longer stable and should not be entered at all.