How did erosion expose granite bedrock in parts of the Pyrenees?

The exposure of granite bedrock in the Pyrenees is a result of long-term geological processes involving tectonic uplift and persistent erosion.

During the mountain-building events of the Eocene and Oligocene epochs, the collision of the Iberian and European tectonic plates caused significant upheaval. This process folded more plastic, recent layers of rock while fracturing and dislocating the rigid, original base of the mountain chain. As these areas were raised, erosion acted incessantly upon the landscape. In the most exposed regions, this weathering process wore away the softer, overlying terrain, eventually uncovering the older Hercynian sedimentary formations and, in some locations, reaching the deeper granitic bedrock.1

Today, these granites, along with other transformed rocks like slates, schists, and limestones turned into marble, form the axial zone or "spine" of the Pyrenees mountain range.1