Models of Archaic period economy in the Lower Pecos River region of southwest Texas and Coahuila, Mexico, are based primarily on coprolite, faunal, and macroplant analysis of materials recovered from rockshelters. The models maintain that during the Middle Archaic period residential mobility is reduced and tethered to rockshelters in canyons near water, and diet dominated by the plant resources lechuguilla (Agave lechuguilla), sotol (Dasylirion texanum), and prickly pear (Opuntia spp.). I use archaeobotanical analysis and actualistic studies to determine the contents of earth-oven features, the number of plant food calories produced by ovens, and the quantity of refuse they generate. Considered within the framework of a diet-breadth model, the data demonstrate that return rates and caloric yields for lechuguilla and sotol processed in earth ovens are typical of a broad spectrum, low-return economy. Intensive use of these low-ranked resources indicates periods of subsistence stress beginning in the Early Archaic period and continuing through the Late Archaic. Use of low-ranked, high-cost resources in canyon zones indicates that food and fuel resources were quickly depleted forcing high residential mobility. Depletion of local resources, not the distribution of water sources governed residential mobility.