Willow River State Park is a 2,891-acre Wisconsin state park located five miles north of Hudson. The centerpiece of the park is Willow Falls, a powerful cascade in a 200-foot deep gorge. Another popular feature is Little Falls Lake, a shallow reservoir on the Willow River. Because of its proximity to Minneapolis-St. Paul it is one of the most visited state parks in Wisconsin. Trilobite fossils found in the lower layers of the gorge indicate the rock is around 600 million years old.