News:

The historic Beverly Bridge over the Columbia River is expected to open to bikes within the next few months, a milestone achievement in the development of the 288-mile Palouse to Cascades State Park Trail that spans much of Washington state.

https://cascade.org/blog/2021/12/washington%E2%80%99s-longest-bike-trail-get-huge-boost-2022-opening-bridge-over-columbia-river?s=09

The article highlights accomplishments regarding a few major bridges.  Between those bridges are good sections and sections of the old railway bed in need of improvements.  There are private property sections where access is still being negotiated.  There are also trail sections with plenty of goat heads to test any pneumatic tire system yet devised and the rider's patience.  There may be highway options to make connections and bypass the worst of the goat heads.  This is still a work in progress.  

The Palouse to Cascades Trail Coalition website Home | My Site (palousetocascadestrail.org) has more info. 

Willy Weir wrote a big article for Adventure Cycling magazine about his trip across Washington on the trail in 2016 20161201_Tiva_Weir.pdf (adventurecycling.org).

I rode from home to Ellensburg using this trail in August 2016.  I hope to ride it all someday.