kayakers and the olympic mountainsA Bit of Natural and Geologic History of the San Juan Islands

The San Juan Islands are a mystical place, carved from massive tectonic events, several ice ages, and the daily weathering of wind and water. Their beauty is unsurpassed and leaves one feeling as if they have traveled to a place which exists outside the rules of the rest of the world. The San Juan Islands have a well-deserved reputation as being one of the most spectacular places in the world to sea kayak.

The San Juan Islands are located in a very unique geographical location. Though most of Western Washington has a reputation for rainy, gray weather, the Olympic Mountains provide a rain shadow for the San Juans. The “banana belt” of Western Washington, San Juan Island receives about half the annual rainfall of Seattle, WA. Often the San Juans are sunny and warm while the rest of the Pacific Northwest is socked in with clouds or fog. On clear summer days views of the Olympics, Cascades, Mt. Baker, Mt. Rainier, Haro Strait, Juan de Fuca Strait, Vancouver Island, and the surrounding archipelago truly make one’s jaw drop in awe. (See these locations on our San Juan Islands map.)

Geological History

The land, which makes up the islands, is much older than the mainland. In fact, it is what geologists term a terrain: a small chunk of an ancient continent, which accreted itself to the mainland millions of years ago.

Geologically, the islands are in the tectonic zone called a “fore-arc basin”, which is essentially a large downward fold in the earth’s crust caused by the collision of the oceanic and continental plates. The islands are slowly being refolded upward as the oceanic plate crushes against and under the continental plate. The islands were also not immune to the presence of several ice ages. At one point over 5000 vertical feet of ice covered the region. The shear mass of this ice literally carved pieces of the land, such as Haro Strait, which extends more than 500 feet below sea level.

Life in the San Juan Islands has long revolved around its surrounding waterways. The San Juan Islands belong to a greater watershed known as the Salish Sea, which stretches from the base of the Olympic Mountains to Georgia Strait in British Columbia. This unique inland water experiences a large amount of flushing as oceanic tides rise and fall, pulling the water through the narrow island passages. This produces an incredibly lush marine environment from the bottom of the food chain up.

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