Big Rock, once known as the Rock of Ages, is a 30-foot (9.1 m) high greenstone erratic and a landmark on Main Street in Coupeville, at one time considered for a city conservation easement.
Big Rock in Coupeville, Washington, and the Wedgwood Rock in Seattle, Washington, are both glacial erratics that originated on Mount Erie before being transported to their current locations.
The [Clinton erratic] rock and Coupeville’s Big Rock were used to calibrate 36Cl radiometric dating due to the well established date they were deposited and began to receive cosmic ray bombardment.