Native American Haplogroups
Michael D. Brown from Emory University estimated that Haplogroup A divided between 27,000 and 57,000 years ago; Antonio Torroni, professor of genetics at the University of Pavia, Italy, estimated that B split sometime between 26,000 and 39,000 years ago and that D split 32,000 to 47,000 years ago; Theodore G. Schurr, professor at the University of Pennsylvania, estimated that C split between 42,000 and 55,000 years ago, and X split 13,000 to 17,000 years ago. 
For anybody who's interested in this, check out the work of Ripan Malhi; he has a few really good papers on the topic. Here's a snippet: "the frequency of haplogroup A is highest in Canada, the eastern United States, and central Mexico, whereas the frequency of haplogroup B is highest in the West and Midwest. Haplogroup C exhibits a uniform frequency throughout North America, except for a notable decrease in frequency in Alaska. Haplogroup D follows a pattern opposite that of C: frequencies are slightly higher in Alaska and lower in the remainder of North America. Haplogroup X exhibits a higher frequency around the Great Lakes and Greenland than in the remainder of North America. The high frequency of haplogroup X in Greenland is an artifact of the interpolating methodology, since no Native American samples typed from Greenland to date can be assigned to haplogroup X (Lorenz and Smith 1996; Saillard et al. 2000). Overall, haplogroups A, B, and X exhibit strong clines. "