I'm impressed you were able to get to genus based on the single photo here...which seemed to provide a poor angle for viewing diagnostic characters (and isn't very sharp or detailed). I'm grateful...as I would have had great difficulty (and likely no success) trying to ID this myself. But after viewing the BugGuide posts for Zabrotes and reviewing the literature, I'm confident your ID is correct...and I can see a distinctive gestalt for the genus in: the tiny size; pale whitish transverse bar on each elytra (at least in CA species); elytra short (leaving much of abdomen exposed); medial white stripe on the large pygidium; antenna length & shape; large, elongate hind coxae appearing "plastered" against the metathorax; etc.

I was glad to find there's a very nice "Handbook of the Bruchidae"(1) for the US & Canada listed on the info page. Its treatment of genus Zabrotes appears to be based on the revision in Kingsolver(1990) (which is slightly more detailed, e.g. includes collection records).

Studying those references indicates there are only 5 species currently known from CA: chandleri, cynthiae, densus, humboldtae, and spectabilis. Z. chandleri can be eliminated due to its conspicuous orange color pattern, but to clearly separate the others one needs: 1) a view of the lower portion of the hind coxae that is usually covered by the base of the hind femur when the beetles are at rest; and 2) characters of the genitalia.

When I learned that Bruchidae are seed feeders, I initially wondered whether these bruchids might feed on Nemacladus seed? But after reading the literature, I highly doubt that's the case. First, bruchids are said to be internal feeders and (mostly) pupate within the seeds. Mature Nemacladus montanus seeds are quite tiny (about 0.8-0.9 mm)...which I'd think too small even for these miniscule beetles (though the adult of one candidate species has 0.7 mm as the lower bound given for its length, but most adult Zabrotes are described as > 1.1 mm). Secondly...although larval host plants are only known for a handful of Zabrotes species...they're all members of the Pea Family (Fabaceae). And thirdly, Zabrotes is thought to be among those bruchids that lay eggs on seeds after they've fallen to the ground(1) (rather than in flowers as seen here). Also, Kingsolver emphasizes that sightings of bruchids on flowers are usually incidental and should not be presumed to indicate a larval host plant association.