Curt Chandler, Post-Gazette photos Recharged by an early morning storm, water from Hell Run cascades over the Hells Hollow Falls at McConnells Mill State Park. The side trip to the falls is a short walk from the Slippery Rock Gorge Trail. Click photo for larger image. Hitting the Trails This is part of a weekly series spotlighting hiking and biking trails in the region. Publication of the series coincides with the Hike for Health project promoted by the state Department of Conservation and Natural Resources, state Department of Health and other agencies to encourage folks to get fit on foot. Related content If you go: Slippery Rock Gorge Trail More photos from this story Previous stories Find previous installments of this series at our Hitting the Trails Index More pictures from all the stories in this series: Hitting the Trails Photo Journal Next week Ghosttown Trail, Johnstown After spending a day hiking the Slippery Rock Gorge Trail, reporter Don Hopey returns to wet his line in one of the more tempting fishing holes in Slippery Rock Creek. Click photo for larger image.

Most people visiting McConnells Mill State Park, a tiny but brilliant geologic gem 40 miles north of Pittsburgh, get out of their cars only to sightsee at the old grist mill, built in 1868, and the covered bridge, built in 1874 and smashingly uncovered by a falling hemlock in March.

Some will stroll past the mill and bridge along the tumbling green creek on the wide and easy Kildoo Trail or Alpha Pass Trail and marvel at the big-as-a-house blocks of sandstone exposed and eroded by glaciers over the past 2 million years.

But relatively few will venture through the 400-foot deep glacial gorge on the 6.2-mile Slippery Rock Gorge Trail, part of the North Country National Scenic Trail.

The blue-blazed route between the Eckert Bridge and the Hells Hollow trail head carries a "moderate to difficult" rating. But readers who have climbed out of their Barcaloungers to follow the Pittsburgh Post-Gazette's summer-long hiking and bicycling series, honing their hiking skills and buffing their bodies in the process, should be ready for the challenge.

It's one well worth taking. The gorge was designated a National Natural Landmark in 1974 and a State Park Natural Area in 1998. It contains rocky outcrops, a boulder-strewn moraine deposited 23,000 years ago by the last of four glaciers to retreat from the area, tumbling waterfalls, rare plants and skyscraping old-growth forest.

Robert Zbegan, a trail maintenance volunteer with the North Country Trail Association, said some of the stands of red and white oak, yellow poplar and beech near Hell Run and above Walnut Flats are "what Native Americans would have seen."

In some cases, he means the actual trees. "They were never logged because of the steep terrain. An Ohio State University study of the gorge done in the 1990s did core borings on some of the trees and counted 290 rings on one," Zbegan said. "It was a white oak, only 32 inches in diameter. Big but not as big as you'd think because trees in the gorge don't grow that fast because of poor soil and lots of competition."

Hikers can start at either end of the gorge trail but, because it's not a loop, should make arrangements for a shuttle or vehicle drop at the opposite end. Traffic on the back country roads can be sparse.

I parked in the gravel parking lot near the end of Cheese Man Road and walked the quarter mile past the old Breakneck Bridge, spanning Breakneck Falls, and down the hill to Eckert Bridge. There also are a couple of parking spots at the bridge over Slippery Rock Creek, near signs that warn kayakers and white water canoeists about the "dangerous water" and "dangerous currents."

Across the bridge, where clouds of white mayflies are caught in the spiderwebs that line the rusted railings, the well-marked trail begins on the left, where more signs warn that the route is "physically demanding" and "only serious hikers in good physical condition should attempt to hike it."

The signs immediately prove too true as the trail undulates over mossy rocks and roots made slippery by a recent rainstorm. Compounding the difficulty of this stretch is the rushing creek, just steps off the trail to the left. It's so pretty as it tumbles and pools around big boulders and pebbly gravel bars that I can't keep my eyes on the trail or stop wishing I had a fly rod in my hand instead of a walking stick.

A little more than a mile in, after the first footbridge, the trail climbs through shale outcrops in a series of steep, short switchbacks to near the rim of the gorge. This is a hard climb where extreme care must be taken not to trip or slip on shale outcrops and exposed roots. At the top, the hardest part of the trail is behind you.

After descending briefly through a side hollow, the trail cuts across the side of the gorge and climbs gradually until it is again high above the creek. Orange and scarlet mushrooms, switched on by the day's rain, look like airport runway lights along the shade-darkened path.

Occasional bright green vistas to the bottom of the gorge open up where the roots of old-growth trees have let go in the thin soil, causing them to domino down the slope.

About 2 1/2 miles from its start, the trail descends steeply to the Walnut Flats area, a broad, alluvial flood plain along the creek, which is more beautiful here than it was near the beginning of the hike, if that's possible.

Just as the trail comes down to the creek, watch for a muddy, unmarked horse trail that climbs straight up the slope to the right. It's a tough, boot-sucking slog back up the side of the gorge, but the payoff humping up this optional route is an opportunity to catch your breath in a 75-acre stand of old-growth trees.

The trail in Walnut Flats winds through hemlock groves before moving higher on the hill and moving away from the creek, finally turning up along Hell Run.

The last two miles of the trail follows Hell Run, mostly near the top of the hollow and through some scattered old growth before dipping to the run. Eventually it joins the Hells Hollow trail, which is wide and graveled and leads to the trail head at the parking lot along Shaffer Road.

If you have any energy left when you get to the juncture of the gorge trail and the Hells Hollow Trail, detour down that path for a quarter-mile walk to Hells Hollow Falls, a cascade of cool water that felt like heaven to my trail-weary feet.