~450 million years ago

• Collision of the micro-continent Avalonia with North America.

• Formation of Bar Harbor Formation (layered sandstone and siltstone).

• Volcanic activity created Cranberry Island Volcanics and ash layers.

~420 million years ago – Granite Formation

• Formation of Cadillac Mountain Granite, largest granite body on the island.

• Shatter zones created where overlying rocks fell into molten granite.

• Medium-grained granite formed west of Cadillac Mountain.

• Later, diabase dikes intruded into granites and surrounding rocks.

Erosion over hundreds of millions of years

• Granite bodies exposed at the surface.

• Softer surrounding rock eroded, leaving resistant granite mountains and ridges.

• Streams and early ecosystems formed in valleys.

2–3 million years ago – Ice Ages Begin

• Northern North America repeatedly covered by ice sheets.

• Each glaciation eroded earlier features, leaving traces of the most recent.

~18,000 years ago – Wisconsin Glaciation Maximum

• Ice sheets reached southern Maine.

• Glaciers carved U-shaped valleys, polished mountains, and left striations and crescentic gouges.

Post-glacial period (~18,000–9,000 years ago)

• Glaciers receded, leaving glacial erratics and deposits of rock, sand, and gravel.

• Melting ice caused sea invasion in coastal Maine; formation of islands, beaches, and sea caves.

• Lakes formed in valleys dammed by glacial debris (e.g., Jordan Pond).

• Land rebounded; plants, animals, and humans colonized the area by ~9,000 years ago.

Present Day

• Ongoing erosion shapes granite ridges, cliffs, and rubble fields.

• Coastal processes create beaches, cobble shores, and salt marshes.

• Landscape continues to evolve due to water, wind, waves, and human impact.