The Hollywood Islands is a large group of islands that are part of greater Hollywood, although some have claims of independence. Many of these islands exist, and have active volcanoes, due to the geological effects of the Big One. Others have been artificially created, or imported from elsewhere on the globe.
Although there had always been small islands off the west coast, in the wake of the Big One there were suddenly a lot more. Due to the unusual distortions in space and time caused by the Big One, some may have existed in parallel dimensions for millions of years, or possibly do not actually exist at all.