In 1882 he moved to
Washington, D.C. to work in the
US Geological Survey, and in 1888 co-founded the
National Geographic Society. His two most influential surveys were in the 20th century; the first in 1912 to determine
Maryland's border with
West Virginia, and the second in 1927 on the
Red River to determine the border between
Texas and
Oklahoma. Both involved
Supreme Court decisions. He died aged 77 in
Sibley Hospital on August 5, 1939. ==References==