The route between Portland and Longview is unpleasant because the main road connecting the two is interstate 5. I-5 does not allow bicycles, and even if it did, you wouldn’t want to cycle it! If I were to skip any segment altogether, this would be it, since even the alternative US 30 is not a very attractive ride. If you decide to do it, you will begin with a Columbia river crossing at Longview, then cycle between Rainier and Portland.
You can cycle this segment in either direction or try the extension for a much more pleasurable experience. I like to do the segment Southbound so that there is no pressure to catch the train at the end of your ride.
From the Kelso/Longview Amtrak station, you have to cross the Lewis and Clark bridge to Rainier. The bridge is not designed to allow a pleasant experience for cyclists, and the ride through Longview from the train station is almost entirely industrial. I only recommend this segment for those intent on doing all the segments of the Seattle to Portland ride to completion.
Following US 30 south from Rainier, you will pass through St. Helens, a tiny but charming town with several old buildings, made famous by the filming of the movie Twilight. There’s a small museum highlighting this. In the summertime, there are concerts along its ideal setting on the Columbia river. Depending on your time, you can stop to visit here or continue on to Scapoose.
At the north end of Scappoose, you cross the Scappoose/Vernonia highway. If you take a left here, you can head down to Chapman landing on the CrownZ trail. This is a launch point for kayakers exploring the Scappoose bay.
The last leg to Portland passes Linnton and the St. John’s bridge. Cross the bridge to get to north Portland, or continue south to get to the Portland Amtrak station. As you enter the industrial part of Portland, take the Kittridge avenue bridge to Front Avenue. Front turns into Naito before you arrive at the Amtrak station.
Depending on the direction you’re headed, this will either be your first or last segment. The nice thing about these rides is that they can be done individually on different weekends. From Kelso/Longview Amtrak station, you can ride to Centralia.