Rib Mountain State Park, the Quarry, Mosinee Hill, and Hardwood Hill are made from quartzite that was once sandstone. The sandstone, eroded from an ancient mountain range that covered a vast part of northern Wisconsin, was deposited between 1.6 and 1.8 billion years ago. It then underwent metamorphism and changed into quartzite. This quartzite is surrounded by Wausau Syenite which was emplaced underneath Wisconsin approximately 1.5 Billion years ago as part of the Wolf River Batholith.
