Sites -> Fort Vancouver National Site -> Place -> Terrain

Silt over Lava

The Lower Columbia River Valley is an extensive floodplain, where layer upon layer of gravel, sand and silt cover a base of ancient volcanic basalt rock. Seasonal flooding continually deposited more sand and silt in the area, until construction along the riverfront and dams controlled the flow.

One special feature of the Vancouver region is the active volcano Mount St Helens. Its 1980 eruption is the only one is recent memory, but the young volcano has been active for 4000 years. Since 1400 C.E., Mount St Helens had erupted about once every century.

Before settlement, the Reserve site was a patchwork of prairie, forest, and wetlands. Now one small section of riverfront remains as floodplain. Behind the historic officers’ housing, a few old conifers remain from the earlier thick forest.

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