You are on a service road for the entire hike.
These are the parking coordinates:
N47° 49.982
W122° 02.688
There is no parking area. You park on one side or the other on a dead end road stopping at a gate. You might want to look at a map before you drive around looking for the parking.
Your looking for a Loc-n-loc cylindrical container.
Pack a lunch and continue up into the park after you find the cache. Great exercise! Or you can take the long way and come in from the main park enterance.
Have fun!
Sorry for the inattention. Thanks for all the emails. Although I don't answer them. Cache on!