Scarcely interrupted by accessible passes and pierced in only two places by railroad tunnels, the Pyrenees are an ideal natural boundary between the Iberian Peninsula and the rest of Europe. The northern flank of the Pyrenees is characterized by a series of large alluvial deposits that fan out across southwestern France. The darker, roughly triangular area in southwest France is part of the forested Aquitaine Basin.
The southern flank of the Pyrenees (Spain) is characterized by aridity and very rugged, mountainous conditions. Human settlement is sparse throughout the Pyrenees. However, because the region is rich in mineral waters, there are dozens of mineral water resorts, and winter sports attract visitors from southwestern France.
The very small mountainous country of Andorra (not distinguishable in this photograph) has survived in an inaccessible upper valley of the Pyrenees.