I agree with the Columbian Exposition/Ancient Tartaria stuff. But this was interesting too - If you bothered to look, the footprints in question were of ordinary size. The Giant 'big foot' stuff was from the thirties, when they found mammoth and sloth prints, and given their indistinct nature, these were confused with human prints.

The point is: the peeps that were heavily covered by the media, were dating the footprints by carbon-dating a plant that lives under water, found at the bottom of the prints. Ground water has a way of aging the results, because the carbon that is absorbed by the plants comes from buried carbon, not atmospheric carbon. The anomaly is also seasonal - in summer the water table is lower, so the results will be older, so to speak. So, carbon-dating that particular plant, or any under-water plant is a very unstable dating technique.