After Burlington you cycle all along the highway 20, mostly flat until Newhalem. There is also a bike path and a backroad until Concrete. (Yes, its called like this and yes there is a reason for it…)
But the traffic on the highway is reasonable and the shoulders are wide. You follow the Skagit River which is full of turquoise water and flows in an incredible forest. All lush and green, old trees with trunks covered completely in moss. Lovely, no wonder this is the “Evergreen State”.
Newhalem is the last place before the roads starts climbing. It is the central for the dams above in the valley and probably belongs enirely to the electricity company. It has a small store but its expensive and they sell mostly chips and popcorn so you better shop in Marblemount. There is a nice campsite 10 miles after Newhalem called Colonial Creek. It’s the last one before the passes and it saves you some pclimbing the next day.