Thousands of artifacts dating to between 13,200 and 15,500 years ago were uncovered by researchers led by Michael R. Waters of Texas A&M University. They report the discovery in Friday's edition of the journal Science.
Previously, the Clovis culture was thought to be the first American settlers around 13,000 years ago.
It was "like finding the Holy Grail," Waters said in a telephone interview with the AP. To find what appears to be a large open-air campsite "is really gratifying. Lucky and gratifying."
The trove of 15,528 artifacts, including chipping debris from working stones and 56 tools such as blades, scrapers and choppers, was found in the Buttermilk Creek complex near Austin.
The location is the oldest credible archaeological site in North America, Waters said at a briefing. The artifacts were found in an 8-inch (20 centimeter) layer beneath 5 feet (1.5 meters) of earth and other material from later human occupation at the site.
While there are other pre-Clovis sites across the country, Waters said the new find included significantly more artifacts than the others.
Anthropologist Tom D. Dillehay of Vanderbilt University, who was not part of the research team, said he is concerned that the separation of layers at the site "appears not to be as clear as the authors would have us believe."
University of Oregon archaeologist Dennis L. Jenkins said he was also initially skeptical of the find, commenting "it would have been a hard sell" from many other researchers.
Jenkins said he would have preferred carbon-dating of the specimens, but that couldn't be done because there was no organic material to be tested in the newly found layer.
Steven L. Forman, of the University of Illinois, Chicago, a co-author of the paper, said the team used luminescence dating which can determine when the material was last exposed to light. They took samples by hammering black, sealed copper pipe into the layers.
The Associated Press contributed to this report