Be sure to look at the full-size image (Flickr link below) to see the orange gland-like teeth along the margins of the gorgeously glaucous leaves. Those globular orange growths are very similar looking to the eggs of various pierid butterflies whose larvae commonly devour members of the mustard family. It's believed they've evolved through the selective advantage they provide in deterring female peirids from ovipositing on a plant that appears to already have too many eggs on its foliage (which makes it appear that laying ''more eggs'' would result in insufficient herbage for their larvae to feed on). A number of Streptanthus species exhibit such orange, gland-tipped, marginal teeth.

See this BugGuide link for images of 4 different bee species seen visiting the flowers in this population.