Millions of Years Ago
Millions of years ago, Trempealeau Mountain, the bluffs of Perrot State Park, and the Minnesota upland across the river were all one continuous rock mass. Over time, Cedar Creek, Big Trout Creek, and their tributaries carved channels that would isolate Trempealeau Mountain. This drawing shows that the Mississippi River ran north of the park.
During the last part of the Ice Age, some 50,000 years ago, glacial meltwaters laden with sand, gravel, and debris blocked the river's previous route. This forced the Mississippi River to seek a new channel. This drawing shows how this diversion shifted the boundary between Wisconsin and Minnesota. We can thank the glacier for giving Wisconsin the gift of Perrot State Park.