This is the Pine Creek gorge, also called the Grand Canyon of Pennsylvania. It's about 800 feet deep here, 1400 at its deepest point farther south. Nice hiking all around here. The path visible near the bottom of the canyon on the right side of the creek is an old railroad bed converted to a trail. Notice that this is a recurring theme in the east and the midwest. A Westerner notices that there are a lot more railroads here than in the west, and there are many more that have been abandoned, then converted to bike/hiking paths in very scenic areas.