Geologists have determined that Rib Mountain is more than 1.7 billion years old — one of the oldest rock formations on earth. In fact, three large quartzite hills, or monadnocks, are found here in the Wausau area.
The largest monadnock, Rib Mountain is four miles long and over one mile wide. Its curved, rib-like shape gave the "hill" its name. From this vista, you can see two other monadnocks — Mosinee Hill, a dumbbell-shaped formation slightly to the southeast, and Hardwood Hill, beyond that to the southwest.
The quartzite found in these formations is some of the hardest rock in nature. Early miners hauled rock from Rib Mountain with teams of horses and used the quartz in making abrasives like sandpaper.
[caption] An earlier view of Rib Mountain from the vicinity of Mosinee Hill.