Across from San Jacinto towards Big Bear is the larger San Gorgonio Wilderness which has several trail camps along it’s length. You can get your overnight permits online at the SGWA.org website. I usually do my training hikes for the Sierra Nevada there since the highest peak is 11.5k, or when I just want to hike at elevation but don’t want to drive more than 1.5 hours. You usually can hike there into December, though you may occasionally see a few inches of snow.
It’s unfortunate what the fires a few years ago did to the San Jacinto Wilderness area as some of the trails to the east end don’t exist anymore (overgrown). I use to backpack there all the time, but the places I often camped at, below the state park, just aren’t available anymore.
If you don’t mind an out and back, the PCT east or west from a trailhead in the Wrightwood area is a bit lower, but still in the trees.
It is possible to backpack Cuyamaca State Park, but it isn’t convenient. There are 2 trailcamps you can camp at, but you can’t park overnight in the state park except at the campground, which isn’t ideally placed to do a loop at those trail camps. The only time I did it, I signed up at the rangers office for the 2 trailcamps, drove outside the park to a trailhead near the PCT (a small one that didn’t have a sign against overnight parking as the numerous van life people have caused restrictions to be placed in the area) and hiked in to start and back out at the end. I would recommend doing it when the temperatures are cooler than October. I did it right after Christmas.
Mt Laguna is a nice area, but you are only in the trees for a short distance, before you drop out of them. Definitely would recommend doing it when the temperatures are cooler.
