I just started backpacking recently so I’m not too seasoned like everyone else here. After some research, though, my friends and I are planning to hike a trail from Islip Saddle to Little Timmy campground in the Angeles National Forest that’s about 4 miles round trip. We’re continuing on to Mt. Baden-Powell for 16 miles round trip but I’ve read there’s Mt. Islip nearby for 6.3 miles round trip.
You can also hike from Crystal Lake Campgrounds to Little Jimmy for 6-7 miles round trip.
Good luck on your adventures!