A Google search for 'rubik's cube competitions' led me to the World Cube Association website in a matter of seconds. Try to figure things out for yourself before asking such elementary questions next time.
There you go. All the competitions that have been planned and announced. If you want to know when there's a competition in [insert location here], just keep your eye on that page. It lists ALL of them. Local, national, international, EVERYTHING.
There are enough official competitions and delegates in the LA area such that an unofficial competition is practically pointless.
Even unofficial competitions will be announced somewhere. Frequent cubing forums and check out sites like speedcubing.com regularly. Nobody will be making it their personal job to come and specially inform you.
really the point of a forum is to expand collective knowledge and advance ideas as a group, not a place for the lazy to troll the hardworking for answers, especially considering la is one of the major epicenters of cubing