Arnold Hague (December 3, 1840 – May 14, 1917) was an American geologist who did many geological surveys in the U.S., of which the best known was that for Yellowstone National Park.In 1867 he returned to the United States, and was appointed assistant geologist on the U. S. geological exploration of the 40th parallel under Clarence King.On the termination of this work in 1877, he received the appointment of government geologist of Guatemala, and traveled extensively over the republic, visiting the principal mining regions and the canters of volcanic activity.[citation needed] He was a member of scientific societies both in the United States and Europe and in 1885 was elected to the National Academy of Sciences.He made numerous contributions to scientific journals, on lithology and geology, and was the principal author of the following memoirs: