Cedar, especially if it's heartwood (reddish brown, instead of straw color) is one of the longest lasting woods in the desert. On the other hand, that may mean a useful life of only 5 years--as opposed to a life of one year for pine!

Termites dislike the scent of cedar, so it is protected from them until the oils dry out. Splitting is caused by dehydration, mainly, especially when the wood was insufficiently cured at the sawmill. Look for kiln-dried heartwood for maximum service life. Otherwise build the beds out of concrete or masonry.

Good luck! : )

I live in the Central Valley & have triple digit summer heat too. This year I'm putting raised beds behind a fence so the beds are in shade but the plants raise above it to get sun. Anything raised, even pots, will have a higher soil temp than the ground & it'll also take more water. My raised beds in full sun are only 1 ft high. I do that just to add good soil to the hardpan clay we have. Why don't you try just 1 raised bed & see how it survives your summer heat before doing more? I feel your pain...

I will be following this thread closelly since I am on the same boat you are, I live in Yuma Arizona and summers are very hot also.
I have read that using a soaker hose (I think that is the name) under the dirt will help eliminate evaporation and make the system more efficient.