I was going to write to ask which part of Arizona you are located, but then it does not matter because no matter where you are the desert that you need to get across this time of year is realistically too hot. I would highly recommend that you wait much more than a few weeks, realistically speaking more like a few months before the temperatures drop significantly. As I see it, you have two basic choices; A) you could Hitch hike out to the coast anywhere from San Diego to Santa Barbara and ride the coast to Oregon, or.... B) Hitch hike to Ridgecrest and take the 395 heading north and do the Sierra Cascades. Another way to go besides hitch hiking, is to find someone on Craigslist/ ride share that is going in your desired direction.