On the opposite spectrum of hilliness from my PDX-Bremerton route, this one starts and ends in roughly the same area, but goes up and over Mt St Helens rather than the flat Washington coastline.
Wind River Rd and NF-25 provide the most gorgeous (and challenging) portions of the ride, cutting through Gifford Pinchot forest as you ride between Carson and Randle. These roads aren't maintained for winter riding -- which, depending on the year, might delay its opening all the way until June or even July.
When they are open, though, it's gorgeous... and hard. I'll spare details from the elevation profile and just say there's a big volcano there, and you ride up and over it.
The latter half of the ride is a bit more relaxed, but you still have some pleasant roads (and a bit of climbing) after Randle, going up towards Orting. The last forty or so miles uses the Interurban Trail then a variation of the official STP route to wrap up the ride in the University District.
This, of course, is also available to be used in the opposite direction (and again, no cue sheet for that way yet). There's two or three campgrounds with drinking water available as you ride through Gifford Pinchot, and a not-entirely-reliable grocery store near Swift Reservoir. For the northernmost parts -- the ones you'll likely face in the middle of the night if you started in PDX -- I'm not sure of many 24-hour food options, so pack plenty of snacks and probably a third water bottle.
I'm toying with making a Cyclos Montagnards-esque unofficial medal for Oregon or Seattle randonneurs who complete both #1876 and #1877 in a span of a couple of days, with a brevet or permanent in the middle -- maybe call it the lazy man's 1000+K. Check back later.