I too second Mark's idea of Anza Borrego. It's a terrific desert environment, with lots of trails to explore. It's been a few years, but I still dream over my photos of the spring bloom explosion!

It's also not far to Joshua Tree National Monument, & altho it's been loved nearly to death, I wouldn't miss some of the back-country hikes that will take you into wild canyons & palm-fringed springs. Wildlife viewing is spectacular if you take your time, plenty of water & a good map. A dip in some of the boulder tanks is lovely.

http://www.nps.gov/jotr/

Wish I were headed there at this very moment...

Gail In Eugene