From Ohio History Central
Hocking Hills State Park is known for its geologic features of black hand sandstone, including Old Man's Cave, Cedar Falls, and Rock House.
The Black Hand Sandstone, of Early Mississippian age, is responsible for perhaps some of the most significant and prominent scenery in the state. This unit is up to 200 feet thick and composed of almost pure quartz sand and pebbles. In some portions, it is dominated by white, rounded quartz pebbles and forms a conglomerate. Because of its thickness and resistance to erosion, the Black Hand forms shear cliffs and gorges. A less well-cemented middle portion of the unit weathers more rapidly than the upper or lower parts and forms recesses or rock-shelter caves. Waterfalls are common where the Black Hand is exposed. Hocking