Around 300 million years ago, the Ancestral Rockies stood here. Over time, wind and water eroded the peaks into swift streams full of sediments, which were eventually pressed and cemented into solid rock. These new rocks formed as sands rich in iron oxide that created red sandstone, muds that became softer, more delicate shales, and a mixture of sand and pebbles called conglomerate. More than 60 million years ago, Balanced Rock was exposed when the existing Rocky Mountains rose. Its current shape developed because the soft bottom layer of shale eroded much faster than the harder sandstone and conglomerate above, leaving a narrow pedestal that has supported its 700-ton weight for thousands of years.