Rib Mountain, one of three large quartzite monadnocks in the Wausau area, is more than 1.7 billion years old and is among the oldest rock formations on earth. The largest of the three, it is four miles long and over one mile wide, and its curved, rib-like shape gave it its name. From this vista, the other two monadnocks are visible as well: Mosinee Hill, a dumbbell-shaped formation slightly to the southeast, and Hardwood Hill, beyond that to the southwest. The quartzite in these formations is some of the hardest rock in nature, and early miners hauled rock from Rib Mountain with teams of horses and used the quartz in making abrasives such as sandpaper.