For over 50 years, researchers have suggested that increased regional rainfall over the highland deserts of Mesoamerica's northwestern frontier zone during the Classic period (AD 200-900) allowed for the colonization of the zone by farming groups who originated from Central and/or West Mexico. A severe and prolonged drought is hypothesized to have later provoked the abandonment of the region by these sedentary populations by AD 900. However, very little research has been carried out in the zone to detect evidence of this proposed climate change. I present results from the first systematic study of wood charcoal from the northwestern frontier, comparing the data from three Classic period ceremonial centers that span the region's north-south gradient of intensifying aridity. The results indicate that the strongest evidence of environmental degradation is found in the south (where average annual rainfall is the highest), while the sites located farther north (with lower annual rainfall) demonstrate more stable use of wood resources. These findings suggest that anthropogenic impact played a more significant role in regional abandonment than climate change, and that the current models of the process of the collapse in the northwestern frontier may need to be reconsidered.