Why are the rocks at Devil’s Lake State Park pink or purple? This is a pretty common question. The stone is quartzite, specifically “Baraboo Quartzite” which is as much as 1.5 billion years old and among some of the oldest exposed rock in North America! All Quartzite used to be sandstone that changed (metamorphosed) through time to become the rock you see today. While most quartzite is white or gray, Baraboo Quartzite can range from light pinks to dark purples because it contains iron oxide hematite and other impurities which colored the rock. If you like, you can just say it’s “rust”.