This is an Echium (I don’t know which species), a large, towering flower related to borage that is so prolific around San Francisco you can’t seem to turn a corner without bumping into one. I must have taken several dozen photos in a variety of media (digital, polaroid, film, macro) as evidence. Another plant thoroughly documented and recorded.
My attraction to this plant lies in the fact that it reminds me of one of my favourite local wildflowers Viper’s Bugloss (Echium vulgare), which is not surprising since they are in the same genus. These enormous San Francisco echiums are basically monster-sized versions of the same plant.