I prefer the DNA study done by professor Stephen Oppenheimer. He places the first immigrants at Meadowcroft at 25,000 years ago. It is my opinion that these are the folks that are most closely related to Kennewick Man. The Obijawi(sp) Indians have the highest % of the the "X" halotype (European) gene than all others in this country. Here is an excellent map that shows this journey as created by Professor Oppenheimer:
Interesting article. Check out link at #4.