In 1927 H.G. Merriam asked Coates to help him with a literary magazine, The Frontier: A Magazine of the West. She started writing articles and poems for the magazine and before long became the assistant Editor. Merriam encouraged her to get her work published, helped her find publishers, and in 1931 she published her first short story collection, Black Cherries, and her first book of poems, Mead & Mangel-Wurzel. Coates worked for the magazine based in of North West Montana, until it stopped circulating in 1939. During the Great Depression, Coates helped write the WPA Federal Writers' Project Montana state guidebook. Coates stopped writing seriously in the 1930s, but she continued to participate in her favorite form of writing through letters. After her death, her letters were collected and used to illustrate her life in a biography written by Lee Rostad.