I would call kevin at tribe its a tri store but they sell moutain bike and its a great store. 480-421-9442. Mcdowell moutain park is long but a great beginer course (permberton trail ) email me if you have any q's.
I have heard that fountain hills has some good stuff as well as a network north of the 60 on Power. I think you might have to pay at that one though... http://www.crankcollective.com has been mapping some stuff in the area. Good info there...
forget training for the dawn til dusk... ride trails virtually..... check this out:
..okay maybe I'll still train a bit.