If you live in Oro Valley, 50-Year Trail will be your best bet. It has everything from beginner (jeep roads) to extreme technical. Go to Mountain Biking Tucson - Tucson MTB
, and set up an account (free, and no spam) - it's a forum for Tucson Mountain Bikers that will get you hooked up with rides, etc. Also, there is the Sonoran Desert Mountain Bicyclists (Sonoran Desert Mountain Bicyclists - Tucson, Arizona
) which is a local social/advocacy club. Another great place to hook up with riders. If you would like, I am free occasionally on Saturday mornings - I live in Catalina, and frequest the 50-Year - would love to show you around!