I agree with most who are pushing the 250cc class bikes. Yamaha WR250R or Honda CRF250L would be best to start with. Both are light enough to take off-road (and pick up when you crash). Both have wide ratio transmissions and will do highway speeds. DRZ400S is a top heavy beast with a narrow range 5-speed transmission (fail), and the 650 class bikes will be too heavy for a 140lb rider to handle in wet, slippery Pac NW trails.
I would look for a good used Yam WR250R to save a few bucks. It is the best all around bike for your size and needs.
2007 WR250F (plated)