Varnum served as Regimental Quartermaster from November 1876 through October 1879. In 1877, he participated in the Nez Perce War, fighting at the Battle of Canyon Creek, as well as the Battle of Bear Paw from September 30,–October 4,. He continued to serve on the frontier in various forts and married Mary Alice Moore (1865–1935). They had three children, one of whom died two weeks after being born in 1889.
