This actually keyed out relatively easily using the Delphinium key in TJM2...which I (and many I've talked to) find a somewhat uncommon occurrence :-)

Reinforcing the ID here is the fact D. decorum is one of only two species listed in the 1990 ''A Flora of the San Bruno Mountains''. The other species, D. californicum, is a very different looking and distinctive plant. Although many of the D. californicum I've seen recently on San Bruno Mountain are uncharacteristically small, typically full-grown D. californicum are tall (usually a meter or more high, sometimes up to almost 2 meters!), and often grow in somewhat rhizomatous-looking colonies. It's usually has a single stem...rather bushy looking at base...that tapers above with a roughly-conical outline. It has large, full, lower-leaves with narrow sinuses, and a long densely packed infloresence with relatively small flowers...which are relatively ''un''-showy for a Delphinium).