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This 2,546 acre (1,030 ha) Pennsylvania State Park is one of my favorite parks in the Pittsburgh area. Because of its beauty - deep scenic gorge with the restored watermill and a covered bridge - it was chosen as one of the "25 Must-See Pennsylvania State Parks".
In 1852, a gristmill was opened on Slippery Rock Creek and transferred to Thomas McConnell in 1875. McConnell modernized the mill by replacing the water wheel with water turbines and the grind stones with rolling mills, creating one of the first rolling mills in the US.
The mill closed in 1928 and in 1942 ownership was transferred to the Pennsylvania Conservancy. In 1957 the Commonwealth of Pennsylvania took over and created McConnells Mill State Park.
The Covered Bridge that you see near the mill is a Howe truss bridge. It was built in 1874 and it is listed in the National Register of Historic Places.
McConnells Mill State Park has nice hiking trails and I like to suggest the following two which start in opposite sides of the park:
Park your car at the Point Parking Lot (map). There is a restroom in case you need it. Then walk south on McConnells Mill Road to the west of the parking lot against the flow of car traffic. This may be an unusual way to start a hike, but walking down this road that was dynamited through the cliffs is real scenic. After a few minutes you will come to the mill. Go to viewing platform to get a good view of the dam, the mill and the covered bridge. Then walk around the mill and then to the bridge; you can cross the river if you like.
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When you are done taking photos and exploring, walk back towards the dam. Stay on the marked path between the river and the road and follow this trail. The road will soon branch off to the right and the trail will go into the forest near the river. This the Alpha Pass Trail which is marked with blue blaze symbols and from here it will be 0.6 miles back to your car. This trail is of moderate difficulty. I like it because it affords good views of Slippery Rock Creek and you get to see a tall waterfall near the end.
Towards the end of the trail where you need to turn right, it is real difficult to find the blue blaze symbols. You will know that you need to turn right when you see the wooden stairs to your right. Take the stairs (be careful some planks are loose) but don’t go all the way to the top. About mid-way you where the left hand rail is missing, there is a narrow trail to the left by a big rock. Take this trail and you will almost immediately see a bench. This is the short trail (maybe 100 yards) that branches off to Alpha Falls. Be careful, water spray from the falls can make the last part of this trail slippery.
The unnamed creek at the top can dry up during dry periods. It flows through Alpha Pass above the falls before dropping approx. 50ft down at Alpha Falls and then it flows down into Slippery Rock Creek.
When you are done enjoying the falls, go back to the main trail, turn left and go all the up to the street. Then turn right and follow the road for a short hike until you get back to the parking lot.
Hell’s Hollow Falls are probably the most beautiful falls in McConnells Mill State Park. The trail is easy and wide and you will see lots of children here. It is about 0.5 miles to the falls and then the same 0.5 miles back.
Head down to the trail parking lot (map) and take the trail. After about 500ft (150m), Hell’s Hollow Trail branches off to the right over the wooden bridge, while the Slippery Rock Gorge Trail, that will eventually bring you to the mill, continues straight.
While it is possible to get close to the falls without getting wet, you may want to bring towels or bathing suits for your kids. While you can’t swim there, kids will have lots of fun playing in the water.