Answer: I think, given the extremes, that your best bet would be to use native plants. They are quite adaptable, need very little water once established, and will stand up to extremes in temperatures.
I found the following website that contains a database of California native plants and if you enter your zipcode plus your soil type and watering habits, it will generate a list of suitable plants. Once you've come up with a list of suitable plants, you can click on each plant's description to see if it fits the garden space. Have fun with the search engine!
Q&A Library Searching Tips