Lake Pátzcuaro (2,035 m asl), situated in the temperate highland-forest region of central Mexico, was the focus of Postclassic Tarascan civilization. Today, the lake is bordered by wide, swampy flats, which can be interpreted as low-angle fans of colluvial material derived from the deeply eroded, lower-valley side slopes. A gully near the northwest shore exposed two colluvial units: The lower one was dated at 2,300 years B.P. (350 B.C.) at the base of the exposure, while the upper one yielded three 14C ages ranging from 270 years B.P. (A.D. 1680) to "modern." Both units contained abundant charcoal. Pollen studies by Watts and Bradbury (1982) suggest that the first phase was initiated by the widespread introduction of maize cultivation around 1550 B.C. The second, more intense, phase of forest clearance, although it may have begun during the Late Postclassic period, probably culminated during the great expansion of colonial plough agriculture and livestock rearing in the late sixteenth and seventeenth centuries.