The given coordinates will lead you to a stand where you can learn
a little bit about the local history. You will need to gather some
information here to find the next stage.
I've used a simple cipher inspired by playfair to convert
letters to numbers. To code, start with a key, such as "playfair
cipher". Toss out spaces and any repeated letters, yielding
"playfirche". Then assign numbers to the letters starting from
zero:
playfirche
0123456789
Decoding just reverses the process. Note that if the key is
larger than nine different letters can map into the same digit.
That won't matter, since you are only going to use this to go from
letters to numbers.
To find the North coordinate, find out who gave the British one
year to resolve "the oregon question". (Answer is ten letters long,
nine when you remove duplicates). The north coordinate is then:
S S E E E E L
To find the West coordinate, find out who said "Never! Never! We
do not wish to leave our country". And the group he was the leader
of. Answer is 16 letters, 13 when duplicates are removed. The west
coordinate is then:
A B O A U O I O.
I would like to make this an Oregon-themed geocache. Leave items
with some relationship to oregon or oregon history (and not just
because you bought it in a store in Corvallis!)