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. "
"The distribution of mtDNA haplogroups and haplotypes among Uto-Aztecan-speaking groups in the Southwest and in Central Mexico suggests that the spread of Uto-Aztecan was not the result of a population expansion northward caused by the development of maize cultivation, as suggested by Hill (2001). The distribution of nuclear markers such as Albumin*Mexico (Smith et al., 2000), however, suggests that the spread of Uto- Aztecan may have been a predominantly malemediated event."  "Mexican and Central American samples have higher frequencies of haplogroups A2 and B2 when compared with C1 and D1. This is especially relevant in the Pima and Tarahumara samples were C1 is very frequent compared to other Mexican samples."