Archaeological investigations of the effects of anthropogenic fire on the subsistence economies of small-scale societies, particularly those of the prehispanic northern American Southwest, are embryonic in scope and disciplinary impact. When burning has been mentioned in such studies it typically has been with reference to its alleged effectiveness in clearing land or deforesting areas for maize agriculture. In this article, in contrast, we present the results of our initial efforts to estimate the yield and socioecological consequences of cultivating a common fire-responsive ruderal—amaranth—whose growth is enabled by anthropogenic burning of understory vegetation in the Southwest's pinyon-juniper ecosystems. With data from the Upper Basin (northern Arizona), we show that, in an area that is not environmentally conducive to maize production, populations could be supported with systematic, low-intensity anthropogenic fires that promoted the growth of amaranth and other ruderals, such as chenopodium, which consistently dominate archaeobotanical and pollen assemblages recovered from a variety of archaeological and sedimentary contexts in the region. Based on this evidence, as well as modern fire ecological data, we propose that fire-reliant ruderal agriculture, in contrast to maize agriculture, was a widespread, sustainable, and ecologically sound practice that enhanced food supply security independently of variation in soil fertility and precipitation.