It is NOT illegal to catch octo's in California, as long as it is not from a protected area (which is most of the coast) - there are areas btwn LA and SD, and north of Santa Monica where you can catch them. I have the paperwork from DFG to back this statement up - I carry it whenever I go collecting, because rangers and people in general WILL hassle you, regardless of the law.
There are maps on the DFG website for where it's legal. Essentially, any where that it's legal to fish, it's legal to catch an octopus. They are NOT protected (even the GPO, which is a bit surprising). And not all tidepools are automatically protected - but most happen to be in Nat'l Parks, which are protected.