Monday, July 9, 2012

Walk across billion-year-old lava flows

Osceola Bedrock Glades State Natural Area
Topo map, Osceola Glades SNA, courtesy Wisconsin DNR.

Unique ecosystem thrives at site where continent once tore itself apart


Travelers to Wisconsin can hike across billion-year-old lava flows while seeing a rare, unique glade ecosystem when taking the Ridgeview Trial at the Osceola Bedrock Glades State Natural Area.

Located north of Osceola, from Hwy. 35 turn north on County Road S. After passing 93rd Avenue and crossing two creeks (a total of 1.1 miles), turn left (or west) onto the next unpaved road and park there. The trailhead is to the southeast along the roadside.

The trail leads south into the natural area. You can take two loops, one short (9/10 of a mile loop) and the other long (1.5-mile loop; if taking the uphill route, 2.1-mile loop). You may have to briefly walk cross-country on on a deer trail but the vegetation generally is low and easy to pass through.

Begin by heading a tenth of a mile roughly southwest toward a hill. The greenery of the thin-trunked trees forms a marked contrast with the black rock jutting out of the hard ground. For 200 million years, lava flowed across the region, which at the time was a rift zone in which the land to the west and that to the east shifted apart from one another.

One of three
At the hill’s base, turn right and walk about a third of a mile. Because of the hard, flat volcanic bedrock beneath your feet, very few plants can grow here. Most common are ferns, mosses, low-growing herbs and fungi.

The area itself is rare. In fact, only three other bedrock glade ecosystems exist in Wisconsin.

To take the short trail, upon reaching the hill’s corner head up to its top for three tenths of a mile. The hill summit with its outcropping is about half of this distance. The summit with its basalt outcroppings feels more like a West Coast mountain top than a Midwestern hill. At the hill’s base, upon coming to County Road S, go north one fifth of a mile back to your vehicle.

For the longer trail, instead of turning at the hill’s corner go a tenth of a mile northwest to a rock outcropping. The black, moss-covered rocks gives the area an otherworldly feel. Walk around it, and enjoy a blufftop view overlooking the St. Croix River; you’re at about 876 feet elevation. If children are with you, make sure they stay back from the bluff’s edge.

The trail passes through oak woodland and in areas where the volcanic rock is close to the surface, the bedrock glade. The rare prairie fame-flower can be spotted here. In September, the white arrow-leaved aster blooms, which makes for an interesting accent color before tree leaves have changed to their fall colors.

Autumn insects
Despite the harsh environment for plants, a number of animals live in the bedrock glade. With the thin trees, owls are easy to spot. Around Labor Day, some interesting insects come out. The giant swallowtail caterpillar, which looks more like a knotty branch than a furry little creature, can be seen crawling on prickly ash, and you’ll likely sight a lyre-tipped spreadwing perching on a twig-like branch. During the summer, mosquitoes can be ubiquitous, so don’t forget the bug repellent.

The trail loops seventh-tenths of a mile around the back of the hill. At about two-tenths of a mile on this loop, you will join a jeep trail which you can follow for more ease of walking.

On the southeast side of hill's base, when the trail reaches County Road S, head north for a little more than a fifth of a mile back to your vehicle.

Alternately, you can follow a trail west up to the hill summit and then upon coming down it on its west side, rejoin the trail where you began your loop, retracing it back to your vehicle.

Read more about day hiking the scenic riverway in my guidebook Hittin’ the Trail: Day Hiking the St. Croix National Scenic Riverway.