He taught at the University of Colorado, did field work in arid areas, and published articles on land use change. He moved to the University of Minnesota in 1929, where he taught until his death in 1948. In the early 1930s he began work in historical geography which he defined as past regional geography. Brown's books were unique: no geographers continued his research, and the 1948 work remains the only text on the nation's historical geography. Two distinguished historical geographers cited Brown's books as the beginning of modern American historical geography.

Brown began geography graduate work (at the University of Wisconsin) in the early 1920s, when social scientists were developing more specialized research methods, emphasizing first-hand data collections. Some geographers rejected the goals of their discipline's earlier workers--determination of the relationships between man and the environment. Brown helped develop a new geography by his participation in field conferences, concern with accurate source materials, and work in describing and interpreting regions.

Ralph Hall Brown is best known for his two books, Mirror for Americans (1943) and Historical Geography of the United States (1948), in which he reconstructed past American regions through the use of contemporary, primary sources. The books are well-known for their pioneering emphasis on environmental perception, and for his primary sources, a technique later widely imitated by historical geographers. Brown was respected as a leader in the Association of American Geographers, a prolific writer, and original and thorough scholar.