University of Washington Publications in Geology The Geology of the San Juan Islands

RELIEF

The San Juan Islands owe their origin to the partial submergence of a mountain range that crosses Washington Sound in a northwesterly direction. The higher points of the range constitute the islands and reefs, while the valleys and ravines form the channels and harbors. Due to the fact that many of the latter have been greatly modified by glacial erosion, they may be considered as fjord-like in character.

The surface of the region is marked by its abrupt changes in elevation. The maximum point above sea-level is found on Mount Constitution with an altitude of 2409 feet. The deepest sounding recorded in the map-area occurs in Haro Strait near Stuart Island, with a depth of 1356 feet below sea-level. The San Juan Island region therefore presents an extreme relief of 3765 feet.