The San Dimas Experimental Forest is not open to public access. Says Eli R
The total elevation difference for Allison Trail is 5,495 feet, and that is higher than average. Allison Trail has only one trailhead, so you're looking at an in and out walk. Now this great outdoors trail is pretty long, so don't forget to pack enough supplies. Now, this is roughly a 2.5-day backcountry walk, so it's a splendid thing if your backpack is big enough to do the job. Allison Trail goes through some very different elevations, and that means that some parts of the wilderness trail could be very different from other parts of it. With its 17 miles of walking distance; it's considered a longer trek. This region does get very dry sometimes, so do check for current fire restrictions before you go if you plan to bring a stove or make a camp fire.