Here are two of our favorite sites in Southern California:
Okay, so you can't drive there, but you can boat there directly. From Los Angeles head down to Long Beach. From San Diego head up to Dana Point, or up to Long Beach. If you will sail from Long Beach you can check out Howard Hughes great "Spruce Goose" seaplane, and the monumental Queen Mary. You can board any number of vessels heading for Catalina. The trip takes less than an hour.
Catalina is a sizeable island with a fairly steep offshore decline to 80' depths. Check with the local dive shops for seasonal regulations and boundaries for collections. The water runs a little on the chilly side, but a dry-suit is far from necessary. Large Lobster, rays, kelp towers, and schools of fish. Landlubbers take glassbottom boat tours in the area or ride a pseudo submarine that chums to bring in large schools of fish.
At least one of the local dive shops will take you on a serious shark-dive for around a hundred bucks: and look, that ain't bad for a once in a Lifetime Experience you'll talk about for ever! Indeed, more than a few great whites have been spotted in the area. The channel between Catalina and the Mainland is also a migratory route for the largest creatures ever to have lived on Earth: the Blue Whale.
This lovely and swank town is nestled in the hillside bluffs of San Diego. The north end includes Torrey Pines Reserve and the clothing optional Blacks' Beach. Dolphin are frequent frolickers to the area. In Downtown LaJolla are upscale shops and comfortable dining establishments. For a interesting view, visit the LaJolla Shell shop and pay the dollar to descend down through the cave and into the heart of the bluff where there is an ocean entrance.
Diving spots include La Jolla Shores, where you can angle south until you reach the rim of a scalloped submarine canyon. Be careful of your depth here, as the canyon rim can be anywhere from 40 to 120 feet deep. The canyon descends from there in approximately 10 foot escarpments, presumably caused by waterflow and particulate matter stratified by thermoclines. It can be quite cold in the canyon. Be alert for sheepshead and other larger fish. Sting rays, flatfish and small sharks abound in the shallows. Mind your air.
Most people enjoy the sheltered entrance of LaJolla Cove. This site gets crowded at times, but is beautiful by San Diego standards and includes plentiful sea life in the Kelp towers that abound in this underwater preserve.