Los Angeles, often initialised as LA, was a major city in California. A significant portion of LA was the neighbourhood of Hollywood, famed as a global hub for film production. However, other parts of Los Angeles were of occasional interest to the Doctor and his friends, as well as Torchwood.
Circa 33,000 years BC, Eleventh Doctor and Rory Williams visited the site where Los Angeles would one day be built. The TARDIS became stuck in a tar pit, while they encounter a mammoth and a sabre-toothed tiger. (COMIC: The Doctor and the Nurse)
The Second Doctor, Jamie McCrimmon and Victoria Waterfield once found themselves imprisoned in the city by Face-Painter, who somehow stripped them of their faces, and his minion, Rachel. (PROSE: Face-Painter)
On a later occasion, the Second Doctor took Jamie and Zoe Heriot to downtown LA in an effort to make them understand no society, even the most egalitarian-minded ones, could escape the difficulties of poverty. Arriving on a Christmas Eve in the late 20th century, the trio worked at the Midnight Mission and stopped a desperate homeless man named Charlie from robbing the charity. (PROSE: Goodwill Toward Men)
In 1976, two priests who were members of the Order of Saint Peter pursued a vampire from Poland to Los Angeles and destroyed it. One of them stayed behind to found a chapter of the order there, and later became the father of Becky Lee Kowalczyck. (AUDIO: Minuet in Hell)
In the waning months of the 20th century, Los Angeles was home to a shady conglomerate known as InterCom, which aroused the suspicion of UNIT, after it was linked to illegal sales of plutonium. Brigadier Lethbridge-Stewart was joined in his investigations in the city by the Fifth Doctor, Tegan Jovanka and Vislor Turlough in 1999. (PROSE: The King of Terror)
After Miracle Day, a renewed Torchwood team moved to Venice Beach to investigate closely what PhiCorp was up to in LA. Rex Matheson had family in this city. (TV: Escape to LA) Later, Oswald Danes presented the Miracle Rally, greatly raising his public image. (TV: The Categories of Life)
Real world location
Though it's possible that a real world location doesn't exist in the same geographic space in the Doctor Who universe, such cases are few and far between. Thus, the map at right is probably a good indicator of the DWU location of Los Angeles.