[1] The Western Cascades contain many extinct shield volcanoes, cinder cones and lava flows, and the region is highly eroded and heavily forested.

The province is characterized as an older, deeply eroded volcanic range lying west of the more recent High Cascades.

The Western Cascades began to form 40 million years ago with eruptions from a chain of volcanoes near the Eocene shoreline.

Occasional remnants of volcanic necks or plugs marking former vents are the only preserved evidence of the many volcanoes that made up the Western Cascades.

A diverse range of plant species, including numerous endemics, are found in the region, but are especially concentrated near Mount Rainier in Washington and in the Columbia River Gorge.