Around 1150 B.C. foraging bands in many parts of NW Mexico and the American Southwest were occupying small camps and building brush structures. At about the same time a dramatically more intensive occupation was underway at the site of Cerro Juanaquéa in northern Chihuahua, Mexico, where Native Americans constructed almost 500 terraces on a hilltop, expending levels of effort not evidenced in the Southwest for another 2000 years. In order to place this scale of effort in context we built an experimental terrace, made detailed volumetric measurements, estimated the total labor costs, inferred the nature of the labor organization, and evaluated terrace function.