San Diego

San Diego was one of the cities suggested by Diana Goddard to leave Henry van Statten after she ordered for him to be taken away, his memory wiped, and dumped "someplace beginning with S." (TV: Dalek)

Beginning in 1970 and continuing into the 21st century, the city hosted the popular San Diego Comic-Con each summer. Over the years, several incarnations of the Doctor and a number of companions have attended the event, occasionally thwarting evildoers in the process (COMIC: Convention Special, Selfie).

The Year That Never Was
During the Year That Never Was, Martha Jones claimed to have gone to San Diego to collect one of the vials of liquid needed to arm the gun she was allegedly preparing to kill with. (TV: Last of the Time Lords)