no, no, no, take HWY 26 to HWY 35
That would be way more doable on a fixed gear.
Start in PDX, ride marine to troutdale. take the historic highway southeast and then hang a rosco towards sandy. there are some steep grades, but i do them riding a 85 inch gear. long skids are necessary dropping into the canyon, but just stay on the yellow lines. from there its gradual climb out of the chasm and up to govt camp.
oh yeah, use some cross tires because i hear hwy 35 has some gravel on it.
seriously, thats a long fixy ride on 70 inches. i wouldnt try it on more than 65 unless you have an ass and quads like the incredible hulk.