wikipedia). You can find them in California, but also in Brazil, Argentina and other countries. The dystopian film "Elysium" developed this concept further (imdb). The rich live on a protected space station in a close orbit around the earth, the rest of the humanity spends their life on an impoverished earth.
It could have been an interesting topic, as for instance the Justin Timberlake thriller "In Time" (2011) showed. But Neill Blomkamp wasted the theme. The scriptwriter and director of this botch delivered just an action movie to entertain unaspiring adolescent.
You don´t learn much about Elysium and the alleged superior technology & lifestyle. Instead the flick is full of fight scenes in the dust. Elysium isn´t science fiction, there is no gram science in it, the audience instead gets a bad rip off of "Mad Max".
Elysium also shows the greed of Hollywood brand names like grand dame Jodie Foster and Matt Damon who used this crap to stockpile their banking accounts.
Watching "Elysium" is a waste of time.