Clatsop Spit - Geology

Geology

After the sea level along the coast rose to its current level approximately 8,500 years ago at the end of the last ice age, seasonal prevailing winds drove the Columbia River's sandy sediment to the Washington beaches in the winter and to Oregon's Clatsop Spit during the summer months. Through this process the sandy beaches grew dynamically to their present size, but it is unlikely they will continue this fast growth. Most of the sediment generated by the Columbia River is now trapped by a series of dams before it reaches the coast. Meanwhile, when the tide is out constantly shifting onshore winds blow sand from the exposed beaches inland on to huge sand dunes. However, during the 1930s most of the spectacular dunes were deliberately controlled by the planting of grass and shrubs to prevent the natural movement of the sand. Now the sand is stabilized by the covering of vegetation and are no longer endlessly in motion, dynamically shaped by the wind.

Clatsop Spit is now part of Fort Stevens State Park.