With a year-round average temperature of 70 degrees, we still enjoy the outdoors in San Diego, even in fall. As an added bonus, the beaches are less crowded even though it's sunny.
Tide pooling is a popular activity in fall and winter during daylight minus tides. Cool little sea creatures reveal themselves in exposed rocky habitats like hermit crabs, sea anemones, sea cucumbers, octopi and more. Two good places for this are La Jolla Shores Beach near Scripps Pier and the Cabrillo National Monument.
We also have a couple of very popular, county-wide events in fall. The first is Kids Free San Diego, which happens in October. During the promotion, kids are free with a paid adult to various museums, theme parks, restaurants, tours, hotels and other fun activities around town. This makes fall one of the most economical times for families to visit San Diego. And, there are also Halloween and Dia de los Muertos celebrations to enjoy.
The bottom line is that fall in San Diego equals good weather, less crowds, annual events and some pretty major discounts.