 Key sites on Mount Desert Island include Cadillac Mountain—the tallest mountain on the eastern coastline and one of the first places in the United States where one can watch the sunrise—a rocky coast featuring Thunder Hole where waves crash loudly into a crevasse around high tides, a sandy swimming beach called Sand Beach, and numerous lakes and ponds.Jordan Pond features the glacially rounded North and South Bubbles (rôche moutonnées) at its northern end, while Echo Lake has the only freshwater swimming beach in the park.Somes Sound is a long fjard formed during a glacial period that reshaped the entire island to its present form, including the U-shaped valleys containing the many ponds and lakes.