An unnamed Middle Pennsylvanian sandstone assigned to the economically-important' coal-bearing Kanawha FormationThese deposits _ were deposited on a lowslying coastal plain around 313 million years ago. The sandstone that forms Hanging Rock was deposited in an ancient riyertrThe undulating loWer surface of the sandstone resulted when the river eroded into underlying maring . sediments containing fossil shells and trace _ fossil tree trunks on the undersurface of the overhang deposited in a prehistoric logjam. I Northern Webster County Improvement Council, Inc. i . 2003 '