Final answer:
Andorra is the country dissected by three narrow valleys that form the Gran Valira, situated in the eastern Pyrenees mountains. The country that is dissected by 3 narrow valleys in a Y shape, which combine into the Gran Valira, is Andorra.
Step-by-step explanation:
The country that is dissected by three narrow valleys in a Y shape, combining into the Gran Valira by the Valira d'Orient, and Valira del Nord, is Andorra. Andorra is a small principality nestled between France and Spain in the eastern Pyrenees mountains. This unique geographical feature distinguishes the Andorran landscape, making it a notable example of European typography.