???
I think I saw this bee emerge from the ground for the first time, but it might have come out of another bee's nest--it was in a large nesting area of Habropoda miserabilis and I've seen other bumble bees on the ground in this area. At first, I thought it was a Melecta, but when I got a closer look in the photos, it seemed to be a bumble bee, though I'm not confident about that and would be happy to learn otherwise.
I caught it (still thinking it was a Melecta at the time) and will try to take more photos of it.
Observed a total of 4 B. melanopygus foraging on Holly blossoms.
About 3/4th of an inch. Leaving at pyrobombus temporarily because I’m not sure if it’s vosnesenskii, californicus or caliginosus. Couldn’t get photos of the abdomen properly.