When the railroad stretched its steel rails across the American West in the 1870s, it opened up a vast expanse of territory. Agriculture quickly followed the railroads, making way for Kansas wheat and Colorado sugar beets and Washington apples. With this new agriculture came an unavoidable need for harvest workers. These were not the year-round hired hands but transients who would show up to harvest the crop and then leave when the work was finished.

Variously called bindlestiffs, fruit tramps, hoboes, and bums, these men--and women and children--were vital to the creation of the...