Great writeup. Along similar lines, the East fork of the San Gabriel river is a bit outside Los Angeles. It has a dead-end road with two tunnels to nowhere, abandoned in the 1960s. Below that is a massive bridge to nowhere that connected to an under-construction road that was abandoned in the 1930s, with all traces of the road largely gone; except the bridge, which is huge and is very much still there. Much more obscure is the PL&P trail, a bit above the bridge. Built and abandoned in the 1910s. All in the same canyon!