Pokemon.com has the information up for the Spring 2012 Pokemon Regional Championships.
Unlike last year, where the regional matches were part of a big Pokemon road show and occurred on consecutive weekends throughout Spring, this year the matches are being run by regional partners and are all taking place on the same day, April 15.
In California, the nearest regional event is still close by my home, just across the bay in Pleasanton.
Links to information about other regional matches are available at Pokemon.com.
The US National Championships will be held in Indianapolis, Indiana on June 30th – July 1st, 2012, and the World Championships will happen in Waikaloa, just up the road from Kona, on the big island of Hawaii on August 10th-12th, 2012.