Here's a detail of one of the (hundreds of) bumblebees that appeared to be hunkering down for the evening on Indian Paintbrush stalks in a large flowering meadow.

Note the orange blob protruding behind the leg at top center of image, which I presume is a pollen load. Also, visible on the enlarged image (but not so well here), I could count 10 flagellomeres on each antenna. This indicates a female according to the 1983 monograph "Bumble Bees and Cuckoo Bumble Bees of California"(1) by Robbin Thorpe, et al. (available as a PDF file here).

I'm guessing this may be Bombus vosnesenskii. Confirmation or correction would be appreciated.