I'm in southern California too and to be honest, I brought my "babies" who are about 5 weeks old inside for the hottest part of the day, probably 12-5. They just weren't tolerating the heat at all, since they hadn't been acclimated to it yet. They did spend their first night outside with no heat lamp though!
The rest of the chicks and hens are outside and doing okay. They're panting a lot, so I'll put some electrolytes in their water per dlhunicorn's recommendation, as well as restrict their scratch feed. I'm on garden watch while DH is working so I'm outside spraying down the garden 3-4 times a day, so I'll mist down the run while I'm out there too. I have other sprinklers for the sloped part of my yard and the mist from those cools down the other side of the run. The moisture dries out so fast and they're dusting a lot in the cool dirt.
I'm going to buy a watermelon today - that sounds fun!