Howdy.
I'm an American living/ diving in Australia for 2 years, but I grew up in San Diego and I have been diving and exploring in Baja for over 40 years.
Guadalupe Island is about a 200 mile boat trip from San Diego and it's awesome, but it's a world away from Baja's Sea of Cortez.
I'd like to recommend Leon's operation Bajaoutpost.com for a place to dive from. La Paz is wonderful, Cabo is a scene, but Loreto is magic. Loreto is the tourist town that never caught on. I Love Loreto for it's near misses and "wanna be" attitude.
In 30 years, it's grown from a sleepy town of 4,000 to a town of 10,000- this is slow growth in Baja Sur terms! Loreto is the old Capital of California, before we took "California Norte" from the Mexicans. Loreto's old town is north of the "new Loreto" which was moved off the arroyo after a nasty chubasco over a century ago.
Loreto's laid back and still small compared to La Paz or Cabo which have both lost their character back in the very early 70's. La Paz has more organized diving, but Loreto is my sentimental favorite. If you take the time to read John Steinbeck's "The Log from the Sea Of Cortez" where he ventured into Baja's waters with Doc Ricketts of Cannery Row fame (he was a real marine biologist!) you'll want to savor the waters in and around Loreto.
Leon, the owner of Baja Outpost, is a blue- eyed Argentnian that moved from the waters of Catalina, California to Loreto after years of looking for the "right spot" to open a modest dive resort.
Leon's love for the "Sea" and it's prolific waters is a bonus one cannot find in La Paz or Cabo, where the operators are there for the money. If you want to take in the Sea of Cortez for it's romantic past and see all that is Baja and was Baja, Loreto is where you'll want to go and Leon is your guide.
Diving?
Las Animas is magic. At Las Animas you can see the fishes from the Eastern Pacific mingle with the fishes from the Indio-Pacific. I'd start a conversation with Leon through e-mail about your desires. Leon and his labrador, Bogart, will guide you to what Baja is really about. If it's adventure you're looking for, head to Loreto.
In 2000, with Leon's help, we took 20 people on an 80 mile panga boat trip to San Jose Island and set up a base camp, complete with generators, compressors, tents, food, a cook, and boat hands for a one week diving adventure of Las Animas, El Bajo, and other islands nearby. This IS Baja and Leon can take you there.
If you want "in and out"- go to La Paz or Cabo. If you want to connect to the remanents of the "genuine Baja" head to Leon and Bajaoutpost.
I sound like an advertiser for him don't I?
I made my first trip to Cabo from San Diego over the old dirt road in 1962. I remember......and if you want to feel that flavor.....go there, and avoid La Paz (population 150,000) or the out of control American playground- Cabo.
You won't regret it.
If it's strictly pelagics you're looking for it's the Socorro Islands on a liveaboard that will meet your desires.
here's a fun read about Socorro....
http://www.diveatlas.com/travel/mexico6.asp
Have fun!
shep