Here's another view when the moth partially closed its wings:
And one more with the wings closed further and from a slightly different angle:
The wing pattern seemed distinctive so I sat down with the Moths of Western North America and started looking through the plates with the hope of identifying it.
As often happens when trying to identify moths, it took me a few passes through the plates. The book pictures show moth specimens with their wings spread open. In contrast, I'm usually comparing them to a live moth in the field with its wings closed or partially closed, so it's a little challenging to match up the wing patterns.
I eventually identified this as a species of Caenurgina, a group commonly called forage loopers or clover loopers. [I'm guessing the "looper" portion of the name comes from the caterpillar stage; the caterpillars are of the "inchworm" type.] As caterpillars, Caenurgina often feeds on legumes, and depending on the species, they may favor clovers (Trifolium spp.).