When the Lewis and Clark Expedition traveled through the Columbia River Gorge, it passed towering 1,000-meter (3,000-foot) cliffs of lava. Those cliffs, and the land around the park that commemorates the expedition's winter on the Pacific, record three great geologic events: the birth of a subduction zone, one of Earth's largest outpourings of lava, and the ice-age floods that carved the gorge.
The Lewis and Clark River. Image from the National Park Service's Geologic Resources Inventory.
The park
Lewis and Clark National Historical Park has seven units around the mouth of the Columbia River, stretching about 64 km (40 miles) along the Pacific coast from Cannon Beach, Oregon, to Long Beach, Washington. Established as Fort Clatsop National Memorial on May 29, 1958, it became a national historical park on October 30, 2004, and covers about 1,376 hectares (3,400 acres).
It commemorates the Corps of Discovery's winter of 1805–1806 at Fort Clatsop, after crossing the continent, when Meriwether Lewis, William Clark and their company gathered supplies, planned the return, and compiled the scientific, cultural and geographic information they had collected, including their encounters with American Indian tribes. The park takes in ancestral homelands of the Chinook and Clatsop tribes, lower Columbia sites where the expedition met Indian communities, and a reconstruction of the fort.
Three events that shaped it
| Event | When | What it left |
|---|---|---|
| The Cascadia Subduction Zone | Formed in the Eocene, when the Juan de Fuca and North American plates collided obliquely off the Pacific Northwest | Folds, faults and inverted topography in the park, from millions of years of ongoing tectonic activity |
| Columbia River basalt | Miocene, about 16 million years ago | Lava that covered roughly 164,000 km² (63,000 square miles) of the Pacific Northwest — including the gorge's towering cliffs |
| The Missoula floods | Pleistocene, about 12,000 years ago | When ice dams failed, cataclysmic floods from Glacial Lake Missoula scoured the landscape and shaped the Columbia River Gorge |
The park belongs to the Pacific Border physiographic province. The Lewis and Clark National Historic Trail, from the Midwestern plains to the Pacific, crosses several more provinces, through Idaho, Illinois, Iowa, Kansas, Missouri, Montana, Nebraska, North Dakota, Oregon, South Dakota and Washington.
Maps and inventories
The Park Service's Geologic Resources Inventory, which produces digital geologic maps and reports for more than 270 natural resource parks, has mapped the park's geology. From oldest to youngest, the units include the Eocene Crescent Formation (basalt lapilli breccia and flows at Fort Columbia, sandstone at Megler, siltstone at Shoalwater Bay), the Eocene–Oligocene Lincoln Creek and Smuggler Cove formations, Pleistocene–Holocene terrace deposits, and Holocene river, estuary and beach sands. A Soil Resources Inventory has been completed; both are on the NPS DataStore.
Sources
Based on "NPS Geodiversity Atlas—Lewis and Clark National and State Historical Parks, Washington and Oregon," National Park Service Geologic Resources Inventory; a work of the United States government in the public domain.
In these publicationsLewis and Clark National Historical Park
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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