City Mouse: "....Hey! I just passed that thing several times this weekend! I always notice it. This is what I know - The words are mine, but the info comes from an article in Adirondack life in 1986, by Jeffery G. Kelly. In 1938, a big rock fell from the cliff and blocked the road. One of the guys working on the road had an idea to carve a stagecoach into it (for some reason). An artist (I forget his name) did the drawing, and it was sandblasted into the rock (not carved).
The artist, Lewis Stacey Brown, was a curator at The Museum of Natural History in NYC for some time. It was etched by the Carnes family in AuSable Forks - their granite and memorial company is still there, right as you pull into town on Route 9N. They did a lot of the memorials in the area, including Stagecoach Rock and the memorial marker at the John Brown site. Surely coaches did pass by, but the article tells us that this wasn't the main stage route - Old Military Road (connecting with Shackett Road in Keene Valley). There was a nearby inn called The Cascade House, which is likely why there were stages passing here.
I took a look around the internet and noticed that the artist must have been around at least as late as the 1980s - he did the illustrations for a kids' book called, "Yes, Helen, There Were Dinosaurs" in 1982. There are a lot of other books under his name, and it seems as if he became rather famous for drawing horses and dinosaurs and such."
Thank you City Mouse!