Catalina is actually closer to Palos Verdes than Laguna Beach.
I've only been to Catalina a few times and I haven't been in a while. Last time I had gone, it was many moons ago (9 years ago) on a college trip before my freshman year and we had gone camping inland while taking in some snorkeling and kayaking. Fun times.
Anyway, Catalina is accessible from a few beach cities in SoCal. Off the top of my head, Catalina Express ferry from Long Beach (and I think San Pedro) and the resort town of Dana Point down in Orange County to Catalina.
Generally, one doesn't think of diving, snorkeling, and kayaking offshore from the mainland, but Catalina is the best location to do all of those things. The one beach I do know of at Catalina is Descanso Beach next to Avalon (there are two towns there, the other is Two Harbors) and it's quite a nice one. Not necessarily ideal for surfing with some small crafts not too far off shore, but it's nice for kayaking and swimming.
If you go inland, there are nature tours where you'll see buffalo, deer, and boars. Oh, and you might also visit the site of where the Cubs spent Spring Training for many a year when William Wrigley had an interest on the island.
I don't remember much of Avalon besides it being a nice, lazy beachside town with its own historical sites, but if you're visiting Catalina, it's definitely for the outdoor activities you can do on the water and inland.