This balanced rock, a gravity defying wonder, happens to be as large as three school buses. The area's sandstone, found in Arches National Park, is colored by a rich red iron oxide. Sandstone has varying degrees of hardness and is eroded away at different rates. One powerful force of erosion is frost wedging. This phenomenon begins when moisture collects in rock cracks, joints and crevices. Most materials shrink when chilled, but water has an unusual property, it expands when frozen. The moisture frozen between the rock creates a tremendous wedging force, causing the rock to separate further. Mid latitude daily freeze and thaw cycles slowly erode away rock layers. Road potholes may be our daily reminder of this geological force.