I had no clue what plant this was when I first photographed it, and Google’s image search didn’t provide much help. Part of my trouble was that I couldn’t guess what the flowers would look like once the buds opened. So I waited for about a week and then went back to check on developments.

This purple milkweed (Asclepias cordifolia) is native to California; but it shares the “purple milkweed” name with the Asclepias purpurascens — an endangered version which is found in the midwestern, southern, and the eastern parts of the U.S. All the milkweed plants are an important food source for monarch butterflies.