Los Angeles County has dozens of trails, some perfect for hiking (whether strenuous or family-friendly), going for a run, mountain biking, equestrian activities, and some are even dog-friendly. They’ve got a great website with information on all the trails, including a super handy way to sort the trails by level of ease or difficulty – just look under the “Explore” tab, or browse by categories.
LA County boasts over 500 miles of trails, and they work in partnership with the National Park Service, California State Parks, the Mountain Recreation and Conservation Authority, the Mountain Restoration Trust, and the Catalina Island Conservancy.