In the mid-1960s they opened the new branch line (shinkansen) to Nagano. Plowing through tunnels at some ghastly speed, it replaced the local slow-train that had wound its way through the mountains for at least 50 years previously (guessing here). The parallel road, its restaurants, ryokan, and gas stands, went the way of countless others when an alternate, faster route is opened.
As well as a near abandoned service garage and its collection of Prince trucks, Renault 4 and motorcycles, the road is also noted for the famous Usui Megane bridge. Famous for its appearance in a number of the Initial D franchises.
I'd like to claim I knew this all the time, and the Silvia wreck, drift marks and marbles down through the mountain pass should have been a clue, but it wasn't until I showed someone else the photographs I discovered the new history as well...
An easy drive from Tokyo if you know how to find it, but one you will need a car to see - sideways or otherwise. See ya! Neko.