Rib Mountain State Park stands on the summit of Rib Mountain, one of Wisconsin's most prominent isolated hills. Like stump-covered fields that suggest forests long since cut, the worn-down stumps of mountains allow geologists to picture the mountains that once covered all of Wisconsin. Over countless ages those mountains were gradually worn down to a plain, leaving only a few harder ridges or peaks, called monadnocks, rising well above the general level. Rib Mountain, the highest rock hill in the state, is one such monadnock, reaching 1940 feet above sea level and nearly 800 feet above the Wisconsin River. Its rock was originally sandstone that became thoroughly cemented into a hard glass-like rock called quartzite, and ripple-marked slabs show that the original material was loose sand washed by waves. The sandstone beds were originally horizontal, but later folding left the quartzite beds in their present nearly vertical position. Rib Mountain stands higher because its quartzite resisted erosion better than the surrounding rock, and its quartzite crags and talus slopes indicate that the area was not glaciated.