i dont think i would take a $100 mountain bike on any serious trail.
You probably find a descent used hard tail for $500 that you could ride the piss out of. Check ebay, mtbr classifeds and pink buy/sell for some good deals on used bikes. Just be careful...ask for lots of good close up pictures if you take this route.
I have never mtb in oregon, but I know there is lots of epic riding there...