Catalina Island  (whose official, but rarely used, name is Santa Catalina Island) is near the southern end of the Channel Islands off the coast of Southern California. It's technically in Los Angeles County and is a popular day trip and vacation destination for locals and tourists.
Santa Catalina is 22 miles from the mainland, despite the lyrics of the Four Preps' song.
Catalina is a world unto itself, a distant asylum from the hustle and bustle of the rest of Southern California. Most of the island is owned by the Catalina Conservancy  which is chartered with protecting its environment.
Many visitors to the island come from cruises offered by Royal Caribbean.
The area codes for Catalina Island are 310 or the soon to be 424.
"City" is a relative term on Catalina - neither Avalon nor Two Harbors are particularly large, with Two Harbors having just a handful of houses and a single general store.
The Casino, built in 1929 by William Wrigley Jr., is a popular landmark and tourist attraction on the western tip of the Avalon beach. It was the tallest building in Los Angeles County at its completion. It features a ballroom, movie theater, and the Catalina Island Museum. There are no gambling facilities; the term casino refers instead to a more traditional Italian definition of casino, meaning social gathering place.
Snorkeling & SCUBA diving from shore - Catalina is a haven for SCUBA divers in Los Angeles area. The main SCUBA diving site from Avalon is Casino Point, right next to the Casino building. Concrete steps have been created, so divers (and snorkelers) can step down a few steps and enter the water. Since Casino Point is north-pointing dive site, it is mostly protected from the heavy surf and waves most of the year. Casino Point is a protected area and NOTHING can be removed from the area. There is a air refill station as well as tank/weights rental right next to the entry point. Common sitings are garibaldi, bat rays, octopus, giant black sea bass, kelp bass, lobsters and horn sharks.
Additional snorkeling can be done at Lovers' Cove, south of the ferry terminal.
Many dive boats depart from various ports in LA area, such as Long Beach and San Pedro, for a day diving trip to various parts of Catalina Island that are otherwise inaccessible via car from Catalina Island. The typical cost is $110-150 and includes breakfast, lunch, and three dives with air fills. Some boats have nitrox at additional cost.
One mile from Avalon (accessible by taxi or bus) is a golf course and a camp ground.
A unique attraction to Catlina Island is the Yellow Semi-Submarine known as "The Nautilus" introuduced in 1999, its design is unique and allows visitors to see the underwater life day and night. These custum build vessel also allows passengers to feed the fish with tis torpedo mechanism.
Classic to Catalina Island are the Glass Bottom Boat and the Interiror trips, that take you to see the Bison that make of Catlina Island their home.