The Appalachian Trail, also called the A.T., is a hiking trail in the Eastern United States, extending almost 2,200 miles (3,540 km) between Springer Mountain in Georgia and Mount Katahdin in Maine, and passing through 14 states. The Appalachian Trail Conservancy claims the Appalachian Trail to be the longest hiking-only trail in the world. More than three million people hike segments of the trail each year. The trail was first proposed in 1921 and completed in 1937. Improvements and changes have continued since then. It became the Appalachian National Scenic Trail under the National Trails System Act of 1968. The trail is maintained by 31 trail clubs and multiple partnerships,and managed by the National Park Service, United States Forest Service, and the nonprofit Appalachian Trail Conservancy. Most of the trail is in forest or wild lands, although some portions traverse towns, roads and farms. From south to north it passes through the states of Georgia, North Carolina, Tennessee, Virginia, West Virginia, Maryland, Pennsylvania, New Jersey, New York, Connecticut, Massachusetts, Vermont, New Hampshire, and Maine. Thru-hikers walk the entire trail in a single season. The number of thru-hikes per year has increased steadily since 2010, with 715 northbound and 133 southbound thru-hikes reported for 2017. The Appalachian Trail Conservancy estimates there are over 3,000 attempts to traverse the entire trail each year, about 25% of which succeed. Many books, documentaries, and websites are dedicated to the pursuit. Some hike from one end to the other, then turn around and thru-hike the trail the other way, known as a "yo-yo".