I can't help you on any of that, but there is a type of arrowhead found there. If you find the right one it could pay for a pretty good chunk of the trip. Some of them go for $600 or $700, maybe even more. They are called Klickitat daggers. Here is a picture of one I did. By did, I mean I knapped it, not found it.
Might pay to take a good look at what you are walking over. Good luck on the trip.