The books chronicle his experiences as a writer in New York and Boston, and his struggle with reconciling that life with his Middle America roots growing up on a farm in Wisconsin. Much of his writing offered realistic glimpses of Midwestern farm life.
Garland also spent time in the American West and wrote The Book of the American Indian (1923) and a series of fiction western romances, including The Captain of the Gray-Horse Troop (1902).
Garland also wrote a biography of Ulysses S. Grant that was published as a series in McClure's Magazine before it was published as a book in 1898. He traveled to Alaska to learn about the gold rush in the Klondike region. His book The Trail of the Gold Seekers (1899) was based on his experiences there.
In 1929, Garland moved to Hollywood. He became interested in psychic phenomena and spent considerable time studying the subject and defending psychic mediums. He wrote Forty Years of Psychic Research (1936). His last book was The Mystery of the Buried Crosses (1939).
He was a prolific writer who produced 46 books as well as short stories, magazine articles, essays, and poems.