William O'Brien Upper Park Trail Hiking Guide
William O'Brien State Park sits in the St. Croix valley just north of Marine on St. Croix, and most visitors never leave the river and the lake. The Upper Park, west of the visitor centre, is where the quiet is: rolling hills of restored oak savanna and prairie, wetlands edged with tamarack, and long views across open ground that feel more like the western prairie than a park an hour from Minneapolis.
Permit: Minnesota state park vehicle permit required: $7 one-day or $35 year-round
The Trail
The Upper Park loop is about 5.3 miles with roughly 380 feet of gain on mapping apps. It rolls gently over hills and through open savanna, with no single hard climb. The park has about 12 miles of trail through woods, wetlands and restored oak savanna, so you can easily shorten or extend the route at trail junctions.
Oak Savanna and Tamaracks
Oak savanna — scattered bur oaks over grassland — was once widespread in Minnesota and is now rare, and William O'Brien is one of the places working to restore it. Autumn is special here: the DNR highlights the golden tamaracks along the Wetland Trail, which turn later than the hardwoods and glow against the dark wetlands.
Lake Alice and Other Closures
Lake Alice was drawn down after a water-control structure failed in August 2025. The beach, fishing pier and accessible canoe launch are closed until construction is finished, which the DNR estimated for fall 2027. The St. Croix public water access was also closed to motorized boats because of low water and sediment. None of this affects the Upper Park trails, which the DNR listed as open.
Winter
In winter the trails are groomed for cross-country skiing, which requires the Great Minnesota Ski Pass. Snowshoeing is limited to the 1.5-mile Riverside Trail, with no snowshoeing west of the visitor centre — so the Upper Park is effectively ski-only once the snow flies. Plan this hike for spring through autumn.
Practicalities
A Minnesota state park vehicle permit is required: $7 for a day or $35 for a year-round permit. The park is open 8 a.m. to 10 p.m. Dogs must be on a leash no longer than six feet and attended at all times. The open savanna has little shade, so bring water and sun protection on hot days, and check for ticks after walking through tall grass.
Hiking tips for William O'Brien Upper Park Trail
- Head west of the visitor centre into the Upper Park to leave the crowds behind.
- Come in October for the golden tamaracks along the Wetland Trail.
- Plan this one for spring through fall — in winter the Upper Park trails are groomed ski trails.
- Bring sun protection; the savanna and prairie offer little shade.
- Keep dogs on a six-foot leash, as Minnesota state parks require.
Nearby trails to explore
- Interstate Park River and Railroad Trail Loop
- Afton North River Trail Loop
- Pike Island Loop
Hike this trail with TrailMates
William O'Brien's Upper Park is a quiet prairie ramble about an hour from Minneapolis. Use TrailMates to find Twin Cities hikers heading up the St. Croix. Download the TrailMates app to connect.