According to Bryan Levick at Five Ounces of Pain, Dana White announced plans for UFC 104 at last nights post-fight press conference for UFC 98:

 

UFC 104 which is scheduled for October 24 will be held at the Staples Center in Los Angeles, California.

The last UFC event in California was UFC 76: Knockout in September of 2007, which was held at the Honda Center in Anaheim.  This will not be the UFC's first trip to the Staples Center either, as UFC 60: Hughes vs. Gracie was held there in May of 2006.

It's worth noting that despite the announcement concerning UFC 104, UFC 102 and 103 have not yet been officially announced by the organization, although 102's card is nearly full, and is expected to take place on August 29th in Portland, Oregon at a yet-to-be-determined venue.  UFC 103 is rumored for a U.K. location in September.

Another interesting side-story surrounding the UFC's return to California, is the fact that "Big" John McCarthy has been re-licensed as a referee by the CSAC in the time since the UFC's last trip to the Golden State, and he has been successfully working shows in recent months.  Although Dana White and McCarthy have had a public falling-out in recent years, White will have no control over the CSAC if they decide to appoint McCarthy as a referee for 104.