Wallula Gap
| Wallula Gap | |
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View of Wallula Gap from Wallula, Washington Main Street
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| Location | Columbia River Basin, Washington state |
| Coordinates | 46°02′40″N 118°56′48″W / 46.04444°N 118.94667°WCoordinates: 46°02′40″N 118°56′48″W / 46.04444°N 118.94667°W |
| Designated | 1980 |
Wallula Gap is a large water gap of the Columbia River through basalt anticlines in the Columbia River Basin in the U.S. state of Washington, just south of the confluence of the Walla Walla and Columbia rivers. It has been recognized as a National Natural Landmark by the National Park Service as a site that provides an important illustration of the geological history of the United States.
In southeastern Washington, eastern Oregon, and southern Idaho, flood basalt flows of extremely fluid basaltic lava spread in all directions from long fissures, building broad fields of gently sloping lava that spread widely over great distances. Along the Snake River in Idaho, and the Columbia River in Washington and Oregon, these lava flows have been extensively exposed by erosion (with extensive displays of columnar basalt), and measure almost 2 km (1.24 mi) in total thickness.
The basalts flows which are visible in the Wallula Gap were laid down during the Miocene Epoch, about 17 million years ago. They are part of the massive fissure flood basalts of the Columbia River Basalt Group. During the basalt eruptions, the southern and western Columbia Plateau, which included the current location of the Wallula Gap, began to fold. The bending (or shear) of the ancient lava flows is clearly visible in the folded layers of basalt exposed in the steep walls of the gap.
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