Whose fault is it? 🤜🏽💥🤛🏽 This photo highlights a reverse fault. In geology a fault occurs as rock units are displaced due to plate tectonics. Here the sandstone of the hanging wall (on the left) is upward of the opposite footwall (on the right). The phenomenal energy and sheer stress in this fault causes slickensides. Friction between the moving rock in the ridge pictured above causes grooves or striations to form in the fault rock (composed mainly of calcite and chalcedony). #Oglala National Park #collectionsite #method