Lithic period in Mesoamerica

The conclusion of this stage may be assigned to approximately 9000 BP (there are differences in opinion between sources which recognise the classification), and the transition to the succeeding Archaic period is not a well-defined one.

Although there was believed to have been anywhere from 20,000 to 60,000 years of post-glacial time in which such immigration could have occurred over the Bering land bridge, the antiquity of human presence in the western hemisphere was popularly fixed at about 5,000 BP ("before present", or 3000 BC).

Fluted points have been found north of Mesoamerica in the states of Sonora and Durango as well as in central Mexico, with proof of a mammoth hunt being uncovered at Santa Isabel Iztapan.

Human presence during this period has been further documented by cranial finds at Peña, Xico, Tepexpan, Santa Maria Astahuacan, and San Vicente Chicoloapan.

Based upon increasing evidence for an earlier antiquity for human presence in the western hemisphere, in 1976 Irving Rouse and Richard MacNeish independently published proposals revising western hemisphere lithic stages, allowing for human occupation as early as 30,000 BP and leaving open the possibility of an even earlier initial arrival.