I have four raised beds I built using redwood about 10 years ago. I'm also in Southern California. My redwood beds are pretty rotten already--they still hold the dirt, but are going to need replacing soon. Regardless of what anyone tells me, I will never use any type of pressure treated wood for my garden beds. The next time I replace my beds, I will probably use a composite decking material like Trex. I know its expensive, but it will be the last time I have to replace them.

I hope the compost from this bin will never go in your vegetable garden. Pressure treated lumber is full of really bad chemicals like arsenic. Your pallets lasted 10 years. I would probably use just standard douglas fir 2x4s from my home center. If you're really concerned about the wood rotting, you can use either redwood or cedar which are also readily available at your home center. I would never put pressure treated lumber anywhere near my garden or compost bin nor would I place the sawdust from cutting pressure treated lumber in my compost pile.