Marie Byrd Land, area of W Antarctica, E of the Ross Shelf Ice and the Ross Sea and S of the Amundsen Sea; the Ford Ranges lie in the northwest part. The region was discovered and claimed for the United States by Richard E. Byrd in 1929. Much of this region was explored during the second Byrd expedition (1933-35) and the U.S. Antarctic Service Expedition (1939-41).