The Birth of an Island

Glacial Stone

The basic materials forming San Juan Island were heaved into place about 40 million years ago. The Juan de Fuca Ridge, an underwater volcanic mountain range, ran north to south a few hundred miles off of the west coast of Washington State. That ridge generated molten rock spreading east in ridges. Meanwhile, North America was sliding west. Enter the Farallon tectonic plate pushing northeast before plunging beneath the North American continent and you have a trench full of giant masses of volcanic basalt plus a jumble of re-crystallized oceanic sedimentary rock crumpling and buckling onto the coast like a Volkswagen Bug rear-ended by a Hummer. Out of this chaos an Island was born. Then, only about 16,000 years ago, huge sheets of glacial ice plowed their way south from Canada gouging out the Straights of Georgia, Straights of Juan de Fuca and Puget Sound transforming Puget Sound from a north flowing watershed into the inland sea we know today. Walls of ice hundreds of feet high sculpted the sharp peaks and plummeting valleys of the Cascade and Olympic mountains that surround San Juan Island. The glaciers retreated leaving deposits of gravel beautifully tumbled into pebbled beaches and the occasional large granite stone standing like a druid monument.