Belt Woods is a nature reserve in Prince George's County, Maryland, U.S., containing the "South Woods", a 43-acre (170,000 m2) woodland which constitutes one of the last stands of old growth hardwood forest on the Atlantic coastal plain. It is a mere 8 miles (13 km) east of Washington, D.C. Many of its white oaks and tulip poplars are more than three feet in diameter and soar more than 100 feet (30 m) before branching. The "South Woods" were designated a National Natural Landmark in 1974.