My wife took me to Salton Sea for my birthday. Fascinating place, bizarre history, blistering heat, sobering ruins, but also strangely beautiful, and site of an ongoing ecological crisis that few Californians are probably aware of.

It's close to the Coachella Valley, but you should have seen the look on the concierge's face when we explained we weren't there to golf and shop. :-) Besides just seeing the sea itself, I recommend Salvation Mountain, Slab City, the obsidian fields, and the world-famous (?) Date Shakes in Westmorland.