The McCullough twins, Suzanne and Lucerne, painted two post office murals: Early Clockmaking (Thomaston, Connecticut) and Black River Canal – 1945 (Boonville, New York). Lucerne is credited with the study for the latter (held by the Smithsonian American Art Museum), while Suzanne gets credit for the study for the former.
You can read a little more about Suzanne at the Island Packet. Lucerne is a little more elusive.