Try this guide service

Driving South on Interstate 5, just past Chehalis, the Chehalis & Centralia facilities may be be seen off to the right. The Milwaukee had a junction here; straight, then a gentle right to Willapa Bay; or diagonal left over to the NP main via a fill of maybe 10 feet to match the NP trackage. Abundant scrub trees now occupy this right-of-way; will be obvious from I5, if traffic allows, or better yet, observe it northbound. Then the turnout switch, with telephone, to NP. Olequa

This elevated section of I5 would have been much shorter if the MILW / NP connection weren't there.

To the East may be seen the state boy's detention facility. Well fenced; has the institutional appearance.

The Milwaukee used this connection twice daily as reparations for the GN + NP + CB&Q merger.
Service to Portland (?); any local service allowed?

At the same time, Milwaukee obtained trackage rights from Renton to Sumas.

Errors and/or omissions?

Looking forward to learning how to access MAPS.

What was the name of the Milwaukee's switch from their Willapa Bay line? Real valuable esoterica. (Look that one up in your dictionary; really applies to us railfans)