A mammoth bone with a carving of a mammoth on it was found in Florida in 2007. Although there were many sites that had human bones interspersed with mammoth bones, this is the first positive proof that humans came to North America prior to the extinction of mammoths, about 13 thousand years ago.
Assuming that it is not a fake. And the current evidence indicates that it is not.
Interestingly, the mammoth is drawn in a style very similar to that current in Europe at that time, fueling the debate that some humans came to America by way of Europe during that period.