The Beginnings of Agriculture
Archaeologists believe that agriculture in North America began with the domestication of corn (also called maize) in what today is southern Mexico. The oldest known corn specimens date from about 4250 B.C., but some researchers believe on the basis of morphological and molecular analyses that corn was domesticated even earlier, in about 7000 B.C. From Mexico, people brought both seeds and an understanding of agriculture north, first to southern Arizona and eventually to places more distant.
Evidence indicates that corn and domesticated squash reached the Colorado Plateau by about 1000 to 2000 B.C., probably as the result of immigrants moving into the area. Archaeologists think the immigrants were Archaic peoples from southern Arizona who moved onto the Colorado Plateau, sharing seeds and their knowledge of plant cultivation with other Archaic peoples who were already there.
The earliest corn and squash found in the Mesa Verde region proper dates from about 400 B.C. However, given that agriculture had been introduced in the larger Colorado Plateau area centuries earlier, it is likely that residents of the Mesa Verde region experimented with agriculture before 400 B.C.—we just haven't found the evidence yet!
So how do archaeologists date the beginnings of corn agriculture? Luckily for archaeologists, early farmers saved and dried corn cobs, which they then used as kindling to start their fires. When burned in a fire, cupules (the part of the cob that holds the kernels) preserve quite well, so archaeologists find them in relatively large quantities in ancient hearths.
Using a special radiocarbon dating technique, physicists are able to determine the ages of very small organic specimens, including burned corn cupules recovered from archaeological sites. The results have allowed archaeologists to date the beginnings of agriculture in various places throughout the Southwest.
Title page for Peoples of the Mesa Verde Region