The 3' gage Catskill Mountain Railway was begun in 1885, and scrapped, without ever being converted to standard gage, in 1919. It was built to 3' gage, even though part of the route -26 miles along Catskill creek (photo location??) was along the right of way of the abandoned Canajoharie & Catskill Rail Road (standard gage 1840-1842) because it was to be a seasonal use line.
The ties in the photo are far too long for even standard gage ones, so the reason behind them is still a mystery. The reason for the track favoring the side of the right of way close to the creek is probably because of concerns about loose rock falling from the hillside on to passing trains. It would appear that there was more than adequate distance between the track and the water, so they left as much room for falling/fallen stone as possible.
____________________ Fix it again, Mr Gates--it still works!"
When I first saw the picture I had the impression that this wasn't 3' gauge. Assuming the ties to be standard gauge I thought this to be a 30" track (looks like slightly more than half of standard gauge). But then I read about 3' gauge tracks and some converted to standard gauge which gave me a bit of puzzling.
You might be right about the rails lying off-center with respect to falling rocks. This might be something I will come back to when I am going to build my layout. It seems to me a quite easy way to give a scene a distinct look with something one doesn't often see as a model.