I found this good writeup today:
An archaeological team from Idaho State University dug up the artifacts at Castle Rocks State Park. They include stone tools and the rocks used to shape them. Skip Lohse, the director of the Idaho Museum of Natural History and the lead member of the ISU team, says some of the tools are believed to be nearly 16,000 years old, which means they predate the Clovis culture until 13,000 years ago. The Clovis culture was thought until recent years to mark the advent of humans in North America.Jlyonlayden, Fantasy or Prehistory?, Oct 2008
You should read the whole article.