The Highline Trail With More Water and Mosquitoes
Located in McConnells Mill State Park, you can hike Slippery Rock Gorge from either end, but hiking from west (Hells Hollow) to east (the Mill) will more often put the sun at your back, or at least side. Plus, you won't dilly-dally as long at the covered bridge / Mill / falls site. (Interesting though they are.) Park signs state it is a vigorous hike of 7.2 miles, and both statements are accurate. They also state it takes 4.5 hours, one way; more like 3, walking time. (With maybe an extra 30 minutes for the many picture taking opportunities.) One way is a great workout; out & back will leave you drenched in sweat, and not just because of Pennsylvania's high humidity.
About those pictures ... if you hike in May or June, you could easily, no exaggeration, cross 50 waterfalls during your hike. Most are very small, but all are scenic. Plus, there are the more significant falls at Hells Hollow and McConnells Mill. The entire hike, you will be accompanied by the sound of rapids and falls on Hell Run and Slippery Rock Creek. If you hike in autumn, there will be fewer falls, but the colors will be fantastic.
Regardless of season -- other than winter -- the entire route is exceedingly lush. There are very few flowers, but more green than you can imagine. It is a mix of mostly deciduous, with some evergreen, and generous helpings of undergrowth. The trail is likely to be very muddy, other than in the evergreen areas where the pine needles provide a clean trail surface. The surface, itself, varies from mostly muddy, to rooty, with some areas of dry natural gravel. It is very up & down, with several strenuous short climbs, particularly in the miles west of Eckert Bridge. (Which could be an alternate pickup point.) You will see very few, if any, people between Hells Hollow and Eckert Bridge.
If you are hiking one way, and want to add a scenic extra mile, hike a half mile down the south bank of Hell Run to the lime kiln and Hell's Hollow Falls. (See alternate route.)
The mile between Eckert Bridge and McConnells Mill is rocky, like creek hiking in Arizona.
Upon reaching McConnells Mill, proceed across the road, slightly left, up a twisty stair to the parking area. Do not follow the road, it is twisty, and narrow, and cars will likely not be expecting pedestrians on it.
Warning: Liberally douse your self and clothes with bug spray before hiking: You will be glad you did. (The mosquitoes are numerous, plus there is always the threat of ticks.) Also, watch out for poison ivy / oak / etc.
Signal: Hells Hollow is 1-bar reception. Most of the hike is no service, including at Eckert Bridge.
Check out the Official Route and Triplog.
This hike is listed as One-Way.
When hiking several trails on a single "hike", log it with a generic name that describes the hike. Then link the trails traveled, check out the example.