Although Achieved At Considerable Expense & Difficult Road Construction Work, This Modern Very High Bridge, Plus Many Considerable Deep Road Cuts In The Mountainside, Which Are At Left, Off Screen.
…Thus This Newer US-95 Highway And Bridge, Avoids the Steep and 21 Tortuous Hairpins of the Old Road!
…This Bridge Is Over White Bird Creek Canyon, And Above, Note Volcanic Rock In the Mountain Side.
…. Below Bridge, In The Foreground, Is Green Along The Creek, Such As Mentioned By ZMM Narrator =>
… “ The road has twisted and rolled over desert hills into a little, narrow thread of green surrounding the town of White Bird, then proceeded on to … ” (Cont. Next)

…In 1968, Robert Pirsig & Chris Likely Followed The Old US-95 Road, Along White Bird Creek, Through town of White Bird, And Then Continued Left Essentially West In The Canyon Seen Under The Bridge. Then Continued To The Southwest, About A Mile, Into The Even Deeper Salmon River Canyon.

Half mile Southwest of White Bird, ID.

…The Narrator’s “then proceeded on“ refers to his and Chris’s following the old road, which is along White Bird Creek, at the base of White Bird Creek Canyon, in /\ Above /\ Photo.
…Please be aware that in 1968, Robert Pirsig & Chris likely followed the old road along White Bird Creek to the left, West, about 1.5 mile, into the even deeper Salmon River Canyon. Of course, the bridge was not there in 1968.
….In the /\ Above /\ Photo => Be sure to study the black color and texture of the rock in this mountain. I believe this is volcanic rock that came from an ancient lava flow called the Columbia River Flood Basalts. As you view the next photos thru number 110-1148, look for this type of rock. About 2/3 of the pictures will clearly show kind of black volcanic rock, especially photos 110-1142 thru 110-1147.
…Many thanks to USCA Geology Professor Allan Dennis for his consultation (and getting it right), concerning the rocks labeled as "volcanic" and "Columbia River Basalts" in these photos.
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(Photo = 111-1140 ...... ZMM Page = 260 ...... WayPt = 284w 1681ft)