If you only have one day, I'd say Channel Islands. The recommendation for the Peace is spot on; it's a fantastic boat with an excellent crew. But if you aren't up in the Ventura area, or don't want to drive, there are boats that go out of the San Pablo harbor. (I believe that's where the Spectre is moored, but I could be wrong.).
The Channel Islands are in a warmer current than Monterey. Monterey has granite pinnacles covered with bright pink corynactis anemones, and California hydrocoral in many pastel shades. You can find that kind of life on San Miguel, which is the westernmost of the typically dived Channel Islands, but nobody goes to San Miguel for a day trip, because it's too far.
Anacapa is where the sea lion rookery is. Whether you get to dive it depends on wind and water conditions. I don't know if the juvenile sea lion population is seasonal or not. I don't live in SoCal -- I've just been fortunate enough to make a handful of trips down there to dive.
Thanks, google says Venture is 1hr15 north of Los Angeles so it would be no problem for me to go there for a day trip, would just leave the family to hang out in LA since we'll be there for a couple of days anyways. Anacapa seems like the closest of the channel islands so maybe it would make sense to do a boat day there while we're in LA, and then a day in Monterey for some shore dives at Lobos Pt? We want to spend a day/night somewhere on the drive up the coast to do a little hike and soak the scenery in a bit, I was thinking Big Sur but I guess Monterey is equally scenic?
---------- Post added April 15th, 2015 at 07:04 AM ----------
There are lots of places to rent gear in So Cal, some near the boats and others not so. It depends on the site. And some boats will rent gear as long as you coordinate with them in advance. If you don't easily get cold, a 7mm with hooded vest and gloves should be OK, and a number of Channel Islands boats have hot tubs. Water temperature in So Cal will probably be mid-50s to low-60s, depending on the spot, wind, currents, etc. The Peace dive boat is great, and so is the Spectre. Trip schedules are on their web sites, and California Dive Boats : The Official Page lists most boats. You can hire a DM as a guide for a lot of boats either through the boat or a local dive shop
California fish are colorful, but if you're expecting everything to be bright tropical colors like Hawaii you won't be satisfied. Garibaldi are brilliant, but you won't typically get the 100+ ft visibility here, so colors might be a little more muted than in some of the pictures above, and a number of the above images are macro shots. Diving in the kelp is magical too, and the light coming through the kelp is spectacular, but again, visibility is variable depending on the conditions.
Anacapa is the closest Channel Island and often has sea lions and kelp, but it depends on where the boat goes based on weather, swell, winds, etc. There is no guarantee of seeing sea lions, just like on the Big Island they don't guarantee manta rays will appear for the nighttime manta ray dives. There's a big sea lion rookery on Santa Barbara Island too, but it's a longer trip and the boat usually leaves around midnight. Each of the Channel Islands is different, as are many shore dive spots, and you never know what you're going to see
Catalina is totally different too. The park in Avalon is a great way to get introduced to So Cal diving, although all the kelp is gone now. Besides the diving, there's a lot to do in Avalon. The mainland diveboats to Catalina don't go to Avalon, just out and back. Time and distance to dive sites in So Cal is typically a bit longer than what you'll get in Hawaii
Some friends are talking about diving Point Lobos this summer. You need to make reservations for shore diving there - Fantastic Diving | Point Lobos Foundation
If you're around Monterey at the end of May, DUI has their demo tour that weekend and you can try drysuit diving - DUI DEMOTOUR Monterey, CA - DUI Online - drysuits
Thanks! I would really like to dive wherever I have the great chance of seeing sea lions, and I would love to dive an impressive kelp forest. I know the former is unpredictable but I imagine it should be fairly easy to predict where kelp forests will be?