Starting from the list in Thorp et al. (Table 3), hopefully we can expand it if there are new records. The only taxonomic update I hit is that Bombus edwardsii is now Bombus melanopygus ssp. edwardsii, so I just left the species.

 - Photo (c) sankax, some rights reserved (CC BY-NC) Comprehensive check list for Genus Bombus
Source: Thorp, R. W., D. S. Horning, Jr. and L. L. Dunning. 1983. Bumble Bees and Cuckoo Bumble Bees of California. Bulletin of the California Insect Survey 23: 1-79, 168 figs. (Link)
kueda Added by kueda on June 18, 2015