The mountain range&#0039;s peaks were once higher than the Rockies, but about 100 million years of erosion has worn them down to about a quarter of their original height.
(s peaks; were; once higher than the Rockies) (about 100 million years of erosion; has worn down; them)
s peaks about 100 million years of erosion
were has worn down
once higher than the Rockies
them