Piegan Mountain, a 9,225-foot peak in Glacier National Park’s Lewis Range, rises beside Piegan Glacier and reflects the park’s glacial and alpine character. Formed from sedimentary rock laid down in ancient shallow seas from the Precambrian through the Jurassic, it took its present structure from the Lewis Overthrust, which began about 170 million years ago when an immense slab of older rock was pushed over younger Cretaceous rock. The mountain lies in an alpine subarctic climate with long, intensely cold, snowy winters and short cool-to-warm summers. It remains a protected scenic summit and a vivid example of the region’s geologic history.