I'll be honest: you will miss Northern California's smooth rolling hills, bike parks, mountains, and forests, but there will probably be a few things you won't miss, as well (traffic, theft, crime, etc.). You'll be pleasantly surprised how much the PHX area has to offer. It's just a totally different environment. I moved here from Utah 10 years ago and never could have imagined how much I would grow to love AZ. I still miss Utah's 5,000-foot climbs/descents, but I don't miss having my local trails buried under snow for 6-8 months a year. I also don't miss having to share trails w/ 100,000 college students along the Wasatch Front.
Obviously, the terrain in the PHX area is mostly rugged Sonoran desert singletrack. There are many different trails in every direction that range from highly technical and rough to smooth and easy. For the most part, the trails are extremely low-traffic. I often ride for 2-3 hours on my 2 nearest and dearest trails w/out seeing anyone else, especially if I ride on a weekday. When I do run into other people, 99% of them are awesome. The scenery/wildlife is always amazing, and when it gets too hot for 2-3 months, you can always take refuge in early morning rides, night rides, or 2-hour trips to Prescott, Sedona, Flagstaff, Payson, or Mt. Lemon.
Bottom line: if you don't love mountain biking in AZ, you have a problem with yourself.