This cache has been in the making for a long time. Before you dash out to the above coordinates in order to key in the numbers for the final, you’ll need two sets of information, and a tool. The first set of info is right here on this page. The second set, some may already have, others may need to dig out. There are some hints here. The tool most should already own. If you came to WP1 in a car, you probably have it.
There are some other caches dotted around Puget Sound with a similar theme, and there’s a cache in Illinois that uses another aspect, but this is the only one I know about that pulls this all together.
You do not need to leave the sidewalk to find WP1! Use your tool before you leave the area of WP1. You may have problems during the time between just before sunset and just after sunrise.
The trip to the final isn't as tough as it used to be, since the park has been finished. Still a possibility for a few muddy spots in the trail, though. No need to bushwack. I've kept the terrain rating the same so as not to mess up someone's Fizzy.
Please tread lightly.
Congrats to towtrkdug, Silly Willy and Maddie's Daddy for the sticking with it for the FTF.
Update, 7/13: The final has been moved back to the park, though not exactly where it was originally. Info at WP1 updated with the new final coords, and hint adjusted.
You can check your answers for this puzzle on GeoChecker.com.