Base2, could you give us an idea of what this trail surface is like?
when I've ridden on some trails that have some gravelly sections, even my 2in nearly slicks do fine, in the dry. Wet and mud would be a different story, although from my experience, once you get past 1.5, and into the 2in range with lower pressures, even reasonable tread like a regular marathon works fine for me, but of course not on mountain bike trail stuff, so it depends.
also, another factor is your bike handling skills and what you are comfortable with. Totally different for different people.
Traillink
East of the Columbia River, the trail is mostly track ballast and fat-tire bikes are recommended. Beginning in Beverly, trail users return to irrigated farmland and wildlife refuges. In this section of the trail, trailheads are planned for Malden, Rosalia, Pandora, and Tekoa.
So far I've been up & down the western section bunches of times. Even making a gravel century once by way of the Samammish Valley Trail. Unless it was on my mountain bike it was always unloaded and recreational on 32mm or 28mm tires of one variety or another.
But being loaded with camping stuff, tent, food, water, etc, combined with the quoted text above & the "loose sand" description of the transit across the army training area has me concerned. It sounds like it would be tough on tires
The Marathon Supremes have my interest, oweing to the ballast rail bed & having been mentioned several times already. The Continentals Top Contact getting honerable mention for their 3 layers of 60 tpi casing.
I am very pleased with the current 559x32 Panaracers & may go larger to ~2 inch size Gravelkings if anyone here has experience on the Eastern section of the trail & can illuminate with first hand knowledge whether my concerns are founded or not.
The Supremes seem to thread the needle in my mind between the Gravelkings lightness & the Top Contacts seeming toughness.
Thus far, you all have been very helpful, & I thank you all.