The First Work: "La Valle dell'Arno"

This is the earliest known drawing by Da Vinci and features the landscape of the Arno Valley and Montelupo Castle.

This work is in the public domain in the United States because it was published (or registered with the U.S. Copyright Office) before January 1, 1923. Courtesy of Wikimedia Commons. 

Source: “Landscape Drawing for Santa Maria Della Neve - by Leonardo Da Vinci.” Leonardodavinci.net, www.leonardodavinci.net/landscape-drawing-for-santa-maria-della-neve.js….