There are dozens of sites similar to that in Clovis New Mexico dated 13,000 years ago, and they all coincide with both younger sites further south, and mass animal extinctions as they go. Now, it's true that the site that enjoys the strongest credentials is the Meadowcroft shelter, but the oldest radiocarbon dates don't make sense, because the plant and animal species associated with them are species living in Pennsylvania in recent times of mild climates ranter than species expected for the glacial times of 16,000 years ago.
The problems many archeologists have with Mt Verde is that the date is based on carbon far from the cave, and (once again) the date stands alone.
Early humans didn't fly by helicopter from Alaska to Meadowcroft and Monte Verde skipping all the landscape in between. Advocates of pre Clovis settlement suggest that, for thousands or even tens of thousands of years, pre-Clovis humans remained at low population densities or poorly visible archaeologically for unknown reasons unprecedented elsewhere in the world.
Check out 'Guns, Germs, and Steel, pp48-49.