Acadia's landscape had its beginnings long before sunbeams first caressed the slopes of Cadillac Mountain. About 500 to 600 million years ago, nameless rivers transported sand, silt, and mud onto the floor of an ancient sea. These sediments built at a rate of about one inch every hundred years until they accreted to depths of thousands of feet. Pressure and heat transformed these sediments into the earliest bedrock. Next, titanic forces lifted and warped the bedrock of the sea into a mountain range, a range perhaps as mighty as the Rockies.

But inexorably, the forces of air, water, and gravity ground these mountains down until little was left. Today, only schists and gneisses, rocks of the Ellsworth formation, remain as testimony to those mountains of long ago. The mountains were built up by tectonic and volcanic forces, and scraped down and shaped by a succession of glaciers. The land sank beneath the weight of mile-deep ice as glaciers inexorably ground their way toward present day Georges Bank, Long Island, and Cape Cod. As the glaciers receded, they filled a vast valley surrounding the mountains with meltwater, creating the Gulf of Maine. Relieved of the great burden of the ice, the land slowly rebounded. These processes, over the eons of time, created the landscape of which Acadia National Park and its mountains are a part.

The shoreline is also a work in progress, constantly being shaped and reshaped by waves and wind and storms. Slowly the ocean works away at the hard edges of the island, carving sea stacks and leaving pockets of beaches filled with surf-rounded cobblestones.