| Western Cascades | |
| Country: | United States |
| State: | Oregon |
| Map: | USA Oregon |
The Western Cascades or Old Cascades are a sub-province of the Cascade Range in the U.S. state of Oregon, between the Willamette Valley and the High Cascades.[1] The Western Cascades contain many extinct shield volcanoes, cinder cones and lava flows, and the region is highly eroded and heavily forested. Deposits of the same age as the Western Cascades are also found in southwest Washington state.
The region was volcanically active from approximately 35 to 17 million years ago. The province is characterized as an older, deeply eroded volcanic range lying west of the more recent High Cascades. The Western Cascades range in elevation from 1700feet on the western margin to 5800feet on the eastern margin. The Western Cascades began to form 40 million years ago with eruptions from a chain of volcanoes near the Eocene shoreline. Volcanic activity gradually shifted to the east in the Miocene and Pliocene.[2]
The Western Cascades are made up almost entirely of slightly deformed and partly altered volcanic flows and pyroclastic rocks, which range in age from late Eocene to late Miocene. These rocks have been heavily dissected by erosion. 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. There are also minor Pliocene to Pleistocene intracanyon lavas derived from the High Cascades or rare local vents. From youngest to oldest, the Western Cascade Range consists of four main units:[2]
Wildlife species richness is not as high in the Western Cascades as it is in other temperate coniferous forests. However, the region is notable for comparatively high amphibian endemism. 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.A number of amphibian targets are either Western Cascades endemics or have a limited distribution. The Cascades torrent salamander (Rhyacotriton cascadae) and Larch Mountain salamander (Plethodon larselli) are restricted to the Western Cascades, whereas Cope’s giant salamander (Dicamptodon copei), Van Dyke’s salamander (Plethodon vandykei), and the Cascades frog (Rana cascadae) occur only in the Western Cascades and Pacific coast. Of these, the Larch Mountain and Van Dyke’s salamanders and the Cascades frog are federal Species of Concern. Most of these amphibians are also closely associated with fast-moving, cold mountain streams.
| Name | Elevation | Location | Last eruption | ||
| meters | feet | Coordinates | |||
| - | - | - | ~0.56 million years ago | ||
| Battle Ax Mountain[3] [4] | - | - | 44.9°N -122.2°W | 1-2 million years ago | |
| - | - | - | - | ||
| - | - | - | - | ||
| - | - | - | ~1.98 million years ago | ||
| - | - | - | - | ||
| - | - | - | ~3 million years ago | ||
| - | - | - | - | ||
Portions of this article include public domain text from the USFS Geomorphic Provinces - Cascades Province - Western Cascades.