What began as a study of the Minneapolis & St. Louis Railway stretched into more than a dozen contributions on Hawkeye state railroad topics. By 1969 Donovan had examined Iowa's “Little Three”: Chicago Great Western, Illinois Central, and Minneapolis & St. Paul as well as the state's “Big Four”: Chicago & North Western; Chicago, Burlington & Quincy; Chicago, Milwaukee, St. Paul & Pacific; and Chicago, Rock Island & Pacific. In addition to these seven core carriers, Donovan covered the state's less prominent railroads: Atchison, Topeka & Santa Fe; Great Northern; and Union Pacific and Wabash. Moreover, he contributed an issue on Iowa's principal interurbans, most of which survived into the 1950s as electric-powered freight-only short lines. In uniting Donovan's articles into a single volume, Iowa Railroads provides the most complete history of Iowa's rail heritage.