I've ridden it from Rattlesnake Lake Trailhead to Ellensbug on an old roadified MTB with 1.5" Armadillos. I dropped the front pressure to 35lbs and ran the rear at 65lbs. My friend used a Trek 520 with 32mm Bontrager road tires. We both found it just fine, although he had to get off and walk his bike over the trestles because the surface is too loose. The trail surface itself is packed gravel in most places, with some exposed pit-run in others. That means boulders ranging in size from 1' drain rock to canteloupe size. The big stuff is buried tho, and actually only sticks up like Euro cobblestones. Not bad at all.

You'll need a good headlight for going thru the 2 mile tunnel under the pass. It's pitch black in there and without a decent light, you can easily run into the walls.

The up grade going to the pass is only about 2%. It's an extremely scenic ride. If you want some ride shots, here's a link to our clubride that day: http://seattlebiketours.org/members/...se_071507.html