Pollen concentrations containing abundant Zea mays pollen grains are AMS radiocarbon dated 3940 ± 40 to 2450 ± 40 14C years BP. The maize pollen is from two prehistoric woodrat (Neotoma) middens that occur in fractures in the south-facing sandstone cliff at Chaco Culture National Historical Park. The diameters of the Archaic-age maize pollen grains are significantly larger than Puebloan and modern maize pollen. The size distributions of the earliest Zea grain populations are not normal, suggesting the possibility that more than one variety of maize is represented by the pollen. The occurrence of large numbers of maize pollen grains as well as pollen from weedy plants indicates the nearby presence of an Archaic cornfield, now buried in alluvial fill adjacent to the cliff. It was also found that the AMS radiocarbon ages of the pollen concentrations differ significantly from the age of twigs from the same woodrat middens. Because of the strong age differences of components of woodrat middens, pollen assemblages should be dated independent of plant macrofossils.