On the Hudson at Newburgh, 1918
Oil on canvas
The Phillips Collection, Washington, D.C.
This painting has a rather remarkable history. It was discovered fairly recently, in 1998 or 1999, underneath another painting by Gifford Beal. You hear about artists painting over their own works from time to time, but that's not what happened in this case; rather, Beal stretched a second canvas over the top of the completed painting. The hidden painting was discovered while cleaning and restoring the work that was been painted on top of the first painting. There's an interesting article about the discovery here.