Moved from Pseudomasaris.

I think it's just a particularly yellow zonalis. I agree it's not marginalis. macnelli and macswaini have much more yellow than this. That kinda leaves zonalis as the only reasonable option.

This is a female, and in your photo she is collecting pollen from the anthers of the Phacelia by using her mandibles and foretarsi. The pollen is subsequently ingested and stored in a 'crop', from which it will later be regurgitated into the nest cell. For taking nectar she'd have her suctorial proboscis extended into the corolla, and body position would be different.
Not sure at this point as to species, though I favor macneilli because of the sulphur yellow, rather than ivory on the closely related marginalis.
Do you have other photos?

Moved from ID Request.