The mountain range that makes the northeastern border of Spain is the Pyrenees. This range stretches over 400 kilometers between regions such as Navarre, Aragon, and Catalonia, and it acts as a natural border between Spain and France. The Pyrenees are known for their significant peaks, including Aneto, which is the highest at 3,404 meters. This mountain range runs horizontally along the north of Spain, marking the boundary with the rest of Europe.
The other options mentioned, such as the Alps, Sierra Nevadas, and Rockies, do not form the northeastern border of Spain. The Alps are in central Europe, Sierra Nevada is in southern Spain, and the Rockies are in North America.
