The shark was ~5 feet long. The next image shows a better side profile:
Note the relatively long snout and large eyes:
And the interesting shape of the tail fin:
Park staff had wondered whether this might be a Brown Smooth-hound Shark (Mustelus henlei). Some of the characteristics seemed like a good match for that species, but there are a few others that I'm not quite sure about.
For example, the maximum size listed for Brown Smooth-hounds is ~3.2 feet, so this shark appears to be larger. And I don't know how consistent tail shape is in this group of sharks, but when I compared pictures of Brown Smooth-hound tails online, this individual's tail was different enough for me to hesitate.
So now I'm going to have to ask for help. Are there any shark experts out there who can assist with this identification? I'll circulate the photos and will report back if anyone offers additional ideas.
At least two species of smooth-hound sharks (Gray and Brown) are known to occur along the West Coast from northern California down to the Gulf of California. Brown Smooth-hound Sharks are apparently common in shallow water bays such as Humboldt, Tomales and San Francisco bays. Gray Smooth-hound Sharks (Mustelus californicus) occur in bays and along rocky shores. For the record, Gray Smooth-hounds do get larger than Browns (up to at least 5.3 feet).
There is more information about both of these sharks on this California Department of Fish and Wildlife web page.
ADDENDUM (6 December 2013): Sorry it's taken me so long, but I need to update the identification of this shark! Several experts have confirmed this as a Soupfin Shark (Galeorhinus galeus). I had started to wonder about this when I checked Bay Fishes of Northern California (Bane and Bane 1971) because they mentioned that small Soupfins could look similar to smooth-hounds...and several of the characters looked right. So a Soupfin Shark it is!