Bombus melanopygus

Bombus melanopygus, the black-tailed bumble bee, black tail bumble bee or orange-rumped bumblebee, is a species of bumblebee native to western North America.
This bee is widely distributed across western North America, from the Pacific to the Rocky Mountains, and from Alaska to Baja California.
There are two forms of the black-tailed bumblebee:

Red form found primarily in higher latitudes of Oregon and points north, and in the Mountain West
Dark color form is most common in California and southern Oregon

This bumblebee can utilize a number of habitat types, including agricultural and urban areas. It is "one of the few bumblebees still found regularly in San Francisco". It feeds on many types of plants, including manzanitas, Ceanothus, goldenbushes, wild buckwheats, lupines, penstemons, rhododendrons, willows, sages, and clovers. It nests underground or aboveground in structures.
This species is a host to the zombie fly.