However, tools, bone structures, genetics, and languages indicate that the early Americans were from many origins, and there have been some sites dated to 15–16,000 years BP.
As it is rare to find human and animal prints, these could add to the literature and experience of footprints – González et al. recommended a further study could be undertaken on the Xalnene markings.
Xenocrysts and phenocrysts were removed in a later dating of the ash material by Mark et al. 2010, which confirmed Renne's proposed age for the Xalnene Tuff.
A comparison with other markings thought to be footprints was undertaken, from various species of humans and in varying substrates and ages.
"Actual pick marks are visible in the quarry but this spalling seems to have caused the print-like depressions with their 'mid-foot' deep points.