The North American region that features mountain building, alpine glaciation, and erosion is the Western Cordillera.

Here's why:

* Mountain Building: The Western Cordillera is a vast mountain range system that stretches from Alaska to Mexico. It was formed by the collision of tectonic plates, resulting in intense uplift and folding of the Earth's crust.

* Alpine Glaciation: The high elevations and rugged terrain of the Western Cordillera are ideal for the formation of alpine glaciers. These glaciers carve out valleys, form cirques, and create U-shaped valleys.

* Erosion: The combination of mountain building and glaciation leads to extensive erosion in the Western Cordillera. Glaciers erode the mountains through abrasion and plucking, while wind, rain, and freeze-thaw cycles further shape the landscape.

Specific examples within the Western Cordillera include:

* Rocky Mountains: The Rockies are known for their dramatic peaks, alpine lakes, and evidence of past glaciation.

* Sierra Nevada: This range in California is famous for its granite peaks, deep canyons, and glacial valleys.

* Cascade Range: This range in the Pacific Northwest is home to active volcanoes, glaciers, and lush forests.

Let me know if you'd like to know more about any specific aspect of the Western Cordillera!