Results of an archaeological and ethnological study of a very large ground stone tool quarry on the lower Colorado River near Bullhead City, Arizona, are presented. The general size and content of the quarry area as understood from survey is described, and the nature of the andesite being selected for tool manufacture is presented. The results of archaeological investigation of 10 discrete production loci is reported, and the kinds of artifacts from them are described. These include broken or aborted preforms, hammerstones , debitage, bracing rocks, and punches. Using results of detailed analysis of these artifacts and data from replicative experiments, a general or idealized reduction strategy for the manufacture of metates is presented. Ethnological and archaeological information are used to suggest that the quarry was utilized by the Mohave Indians, and perhaps their immediate Patayan ancestors. The sociocultural implications of such a technologically sophisticated mode of ground stone tool production are considered. It is suggested that a complex system of ground stone tool production, exchange, and utilization formerly existed among the Mohave, and through the use of comparative ethnological data it is shown that such a system is nearly unique in the Southwest and nearby portions of California and the Great Basin. Using data from a study of metate production in Oaxaca , the form that this system may have taken is presented. The implications of this system for the length of time the quarry was used are explored, and it is shown that the entire production of the quarry could be accounted for in a few hundred years. The presence of a second quarry for ground stone tools near Needles is also documented, and its implications for the use of the andesite quarry are considered. Finally, recommendations are made for future studies at both quarries.