If you want to go further South West you can get to Mojave and/or Joshua Tree, or head more West and go to Death Valley. A bit further and you can get Sequoia National Park and/or Kings Canyon. Swing up North West from there and hit Yosemite. You're starting to get pretty far afield from there though, although if you've got the time you can certainly do it. Don't try and shove locations in at the expense of time at any one place. You can always come back and visit, but while you're at one of the places make sure you visit for how long you want to before moving on.