History of the Columbia Gorge  Highway
The Historic Columbia River Highway was built through the Columbia Gorge between 1914 and 1922, and was the first scenic highway in the United States.
Most of the available river-level land was taken by the railroad, so tunnels, penetrated the rock cliffs while viaducts and bridges spanned the canyons.
Part of the eastern section followed a wagon road built in the 1870s, but the route was shortened and its 20%grades were eliminated by a several sets of horseshoe curve switchbacks.
Eventually, the narrow highway had to be replaced by a multi-lane freeway, and much of the original road was abandoned.  The famous Mitchell Point Tunnel, with its iconic windows, was eliminated when the cliff was blasted away to make space for the Interstate.
One of the highlights of the old highway was Vista House at Crown Point.  The road climbed to the top of a rock promentory, where travelers could get a 360 degree view of the river and gorge.  Doreen is the small one in this 1947 snapshot at the railing by Vista House.
The old road passed through the one-lane Oneonta Tunnel.
Now only pedestrians and  bicycles pass through it (and 15 more miles of road-to-trail bike path.)
Above, western viaduct and tunnel entrance, with railroad immediately below

Left, eastern approach to where the tunnel was, with freeway below and railroad moved north on rock fill