Welcome to BYC
Before you continue on your journey with chickens please read this
https://www.cdfa.ca.gov/ahfss/Animal_Health/Newcastle_Disease_Info.html
Learn all you can about Bio Security...This all started here last spring after a poultry show and they haven't been able to get a handle on it so now everyone in the affected areas is losing their flocks. Also a commercial flock in the area has it as well, no mention of where exactly. So if you are in an affected area you may want to wait and or contact the state or county to find out if you can have chicken or if there is a hold on new flocks
With Newcastle a concern in many areas -- including, I think, your own -- this is VERY important advice.
I'm in LA -- out in the Valley near the Ventura County line. We're not affected yet, happily.
I get my chicks from My Pet Chicken and my experiences with them have been excellent. The downside is you have to wait until they've decided it's safe to ship and you have to order a minimum number of chicks. And when they're due -- they'll advise you when they ship -- someone will have to be available to go right to the post office. Particularly if your delivery date is later when it gets really hot. For my most recent order it was 4 chicks that won't arrive until April.
The upside is you can order almost anything you want. They have filters that will help you to order by egg color, hatch dates, heat resistance* and who knows what else. They are incredibly responsive. I haven't gotten anything from them that wasn't a personal response
specific to the question or concern or instruction I gave. And when my female turned out to be a male, they refunded my purchase price and offered to put me in touch with resources that would help me rehome him (not necessary; I've grown very fond of him).
* So about that heat thing. Take it VERY seriously in Riverside. There are breeds that can adapt to it better than others. There are breeds that will simply die when the temps hit triple digits and
stay there.
Here in the San Fernando Valley, I have to run several large box fans, make copious use of shade cloth, occasionally bring in 10# blocks of ice for the fans to blow over and, still, last year I lost one of my hens.
And you'd be smart to take Riverside heat into consideration when building your coop as well. You want LOTS of ventilation in the enclosed coop -- probably twice what you think is good. Maybe one of those onion-shaped attic fans that operate on hot air drafts. If possible you want an electric supply -- so you can run those fans. You want as much overhang on your roof as possible for shade and then shade cloth out beyond that. I use a light colored high density shade cloth and then I double it. I think I get about 20˚ of cooling from that and that can make the difference between life and death. I'd also increase the space you allot for each hen in the run so they don't have any additional stressors when you can't do anything about 100˚ temps.