In reply to osheye:
FWIW, California is experiencing a severe drought at the moment. Bad news for a lot of people but it does mean that you've got a good chance of finding dry rock to climb on in Yosemite this April. Mountain Project (www.mountainproject.com) is another good source for all kinds of info about various US climbing areas.
Red Rocks and Yosemite are both weekend destinations, not day trip destinations, for anyone based in LA. You can get to Red Rocks from LA without crossing Tioga or any other Sierra Nevada passes. Red Rocks might be a little warm for climbing after early April.
Another option is Joshua Tree National Park, in the Mojave Desert. Closer to LA than Yosemite or Red Rocks, thousands of mostly single pitch routes on quartz monzonite formations, and very popular with Southern Californians. Like Red Rocks, J Tree usually gets very warm after early April.
If the Tioga Pass road opens early this year (and I'm starting to think it will), it might be fun to include a day or so in Tuolumne Meadows if you're spending more than a weekend in Yosemite Valley.
How long will you be in the US? How much time will you have to climb?