Book Excerpt: Walk atop billion-year-old stone on Summit Rock Trail

On the scenic Summit Rock Trail, cabin-goers can hike across or see the results of the three most significant geological events to shape Wisconsin.

The trail takes hikers to the highest point at Wisconsin Interstate State Park south of St. Croix Falls. It runs atop billion-year-old lava flows, the sands of a 500-million-year-old sea, and at the edge of a massive glacial flood from 10,000 years ago.

Interstate State Park sits off State Hwy. 35 just a half-mile mile south of U.S. Hwy. 8 along the St. Croix River. There’s an entrance fee, though a national park pass will get you in for free.

Follow Park Road into Interstate. As it heads south and reaches Lake of the Dalles, look for the parking lot on the road’s right side. The trailhead is at the lot’s north end.

Plan for the park to be busy. It annually receives visitors that outpaces a number of national parks. Additional parking lots can be found on the road’s left side.

The trail heads to the bluff’s highest point and is a dirt surface, so expect an uneven and steep walk at times. Small sections of the 0.5-mile trail (one way) consist of stone and wooden steps through the forested area.

Moss and autumn leaves cover the surrounding rock and ground. Maples, basswood and eastern white pines line the trail. At the top, prickly pear cactus even can be spotted amid the outcroppings.

Though the park includes a campground and is near an urban area, wildlife abounds. Expect to see squirrel, raccoon, deer and dozens of bird varieties along the way. Fox, muskrat and beaver live closer to the river.

The bluff wouldn’t exist if not for a major geological event dating some 1.1 billion years ago. At that time, massive lava flows covered this region of the world. As you near the trail’s top, the black basalt rock you pass and step upon dates from that era.

The highlight of the hike without question is the incredible view of the riverway from the summit. Looking north, the Old Man of the Dalles rock formation is visible just beyond glacial potholes.

The rocks making up the Dalles actually were laid some 515 million years ago when this region sat under a warm shallow sea near the equator. As sediments piled up and were covered over the eons, they hardened into stone; the landscape finally rose above the sea about 345 million years ago.

Then about 10,000 years ago at the end of the last ice age – the third major geological event affecting Wisconsin – a glacial torrent swept through the area when ancient Lake Duluth drained south. This flood broke off the basalt in chunks, created the intriguing cliff formations, and gouged out the deep gorge that is now the river valley.

During the flood, giant eddies from the flow drilled holes into the landscape; these are the potholes between the summit and the Dalles. The largest glacial potholes in the world are just across the river in Minnesota.

Return to the parking lot the same way you came for a one-mile round trip. If you have a full day to spend, a plethora of other activities are held at the park; check at the visitor center for a schedule.

Author Bio:

Rob Bignell is author of “Hittin’ the Trail: Day Hiking Wisconsin and Minnesota Interstate State Parks,” “Hittin’ the Trail: Day Hiking Polk County, Wisconsin,” “Headin’ to the Cabin: Day Hiking Trails of Northwest Wisconsin” and other hiking guidebooks. His website is http://hikeswithtykes.com/hittinthetrail_home.html.