Tunnel is so the trail doesn't wash away. Must get large volumes of water at certain times of the year. Looks lik it is from the Great depresion era. They did lots of work like this. I have found plenty like it on the hudson all done in the 30s. When i get down there again i will post a couple. Love the arched stone. Very gothic.
Thats nice. Lots of stone stairs, roads That zig-zag from the top of the cliffs 100+ feet down to the river. Huge stone retaing walls that are engineering marvels considering were and when they were constructed.