Elk Hill Horse Camping

The American Discovery Trail is a system of recreational trails and roads that collectively form a coast-to-coast hiking and biking trail across the mid-tier of the United States. Horses can also be ridden on most of this trail. The coastal trailheads are the Delmarva Peninsula on the Atlantic Ocean and the northern California coast on the Pacific Ocean. The trail has northern and southern alternates for part of its distance, passing through Chicago and St. Louis respectively. The total length of the trail, including both the north and south routes, is 6,800 miles (10,900 km). The northern route covers 4,834 miles (7,780 km) with the southern route covering 5,057 miles (8,138 km). It is the only non-motorized coast-to-coast trail.
The trail passes through 14 national parks and 16 national forests and uses sections of or connects to five National Scenic Trails, 10 National Historic Trails, and 23 National Recreation Trails. For part of its distance, it is coincident with the North Country Trail, the Buckeye Trail, the Continental Divide Trail, and the Colorado Trail.
The trail passes through the District of Columbia and the following 15 states:

Delaware (45 miles (72 km))
Maryland (270 miles (430 km))
West Virginia (288 miles (463 km))
Ohio (524 miles (843 km))
Indiana (250 miles (400 km))
Illinois (219 miles (352 km))
Kentucky (8.7 miles (14.0 km))
Iowa (512 miles (824 km))
Missouri (343 miles (552 km))
Nebraska (523 miles (842 km))
Kansas (570 miles (920 km))
Colorado (1,153 miles (1,856 km))
Utah (593 miles (954 km))
Nevada (496 miles (798 km))
California (276 miles (444 km))

Read more about Elk Hill Horse at Wikipedia