Foss... it'll definitely keep you on your toes.
On the 700K, we hit this right at sunrise, at mile ~330 on two hours of sleep, and it was like manna from heaven. No drifting off to sleep when you're darting (and, once or twice bunnyhopping) basketball-sized potholes and chunks of dying pavement. Lots of darting up and down 30 or 50 or 100 feet at a time, one nigh unrideable wall that seemed like a 20% grade, then a more mellow stretch to get to Henry Rierson campground, which'll be the turnaround for this 157K.
The campsite has drinkable water and some pit toilets, though I can't 100% guarantee that either will be in service year-round. There's another campground much earlier on Foss -- mile 34 on my cue sheet -- which claims to have drinking water, but I've been burnt before by relying on never-updated county and state park websites, so... I'll assume it's not there 'til I can roll by and inspect in-person.
To get to the awesometastic gravel stretch, it's a really simple route -- Netarts into Tillamook, north on 101, then inland for Miami-Foley Road. Pavement ends right after the recently reopened bridge over the Nehalem River (though the washed-away railroad in the same spot has not been repaired), seven miles after you turn off Miami-Foley.
Bring plenty of snacks and water, some wide-ish tires (David rode this on Nomad 28s and was quite happy), and you'll love it.