Lajia site in northwest China dates to 3800-4000 years ago. Inhabitants died simultaneously in houses from sudden flood. Twelve dental remains from one house yielded five mtDNA haplotypes. Haplotypes indicate close maternal familial relationships. Individuals belonged to haplogroups B, C, D, M*, M10. Analyses used RFLP typing and HVI motifs. Study links to Qijia culture in upper Yellow River. Findings reveal genetic history of Chinese people.