Close to Lake Valsequillo, a site where ancient stone tools have been found (predating the appearance of modern humans in Africa), is Cerro Tolquilla, a volcano that erupted some forty thousand years ago.
In its ashes, a “human” footprint can be seen, which has been been dated to 38,000 +/- 8,570 years ago.
However there is some controversy regarding the age of this “Xalnene” ash. Because Renne et al (2005)  published an article in the prestigious journal Nature where they “dated the Xalnene Ash but with startlingly different results” as they “document that this ash is much older at 1.3 Ma years based on single grain Ar-Ar dating and they suggest that the footprints cannot be human, because of the age but are the result of quarrying operation” 
In Renne’s words: 
Here we show by 40Ar/39Ar dating and corroborating palaeomagnetic data that the basaltic tuff on which the purported footprints are found is 1.30 +/- 0.03 million years old. We conclude that either hominid migration into the Americas occurred very much earlier than previously believed, or that the features in question were not made by humans on recently erupted ash. 
Assuming Renne’s team date is correct, then their first concluison is right, hominids migrated to America earlier than believed, and, if we consider the age of the footprint, then we can identify the hominid: only a Homo erectus could have left the Footprint at that time.
More footprints, photos and details at González website: http://www.mexicanfootprints.co.uk/
However the story does not end in 2005, recently, in May 2010, a new paper by González with Darren Mark  concedes that they:
have accepted that the age of the Xalnene Ash is approximately 1.3 (million years). Considering what we know about the timings of hominid migrations out of Africa up into Europe and Asia, it is highly improbable that hominids could have made it to the America's by 1.3 million years before present. 
That is, highly improbable according to the classic view of anthropologists. Perhaps it is not so, and we are only lacking proof of hominid migration prior to modern human’s appearance on the Earth.
 Silvia Gonzalez and David Huddart, (2007). The Late Pleistocene Human Occupation of Mexico. FUMDHAMentos 7:236-259
 Renne, P., Feinberg, J.M. Waters, M.R., Arroyo-Cabrales, J., Ochoa-Castillo, P., Perez-Campa, M. and Knight, K.B., (2005). Age of Mexican ash with alleged ‘footprints’. Nature, 438, doi:10.1038/nature04425.
 Darren F. Mark, Silvia Gonzalez, David Huddart and Harald Bohnel, (2010). Dating of the Valsequillo volcanic deposits: Resolution of an ongoing archaeological controversy in Central Mexico. Journal of Human Evolution Volume 58, Issue 5, May 2010, pp. 441-445.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia2011 International Year of Forests Copyright 2009-2011 by Austin Whittall ©