Sampling and mtDNA haplogroups in B. attenuatus. Map of California showing the distribution of mtDNA lineages in B. attenuatus (colors) (left). Inset (right) shows populations sampled in the San Francisco Bay Area, with colors also indicating mtDNA haplotypes found in each case. The parallel black lines indicate the approximate location of the Colma Strait (see text). See Figure 3 for more details.