Get to Know Oregon Wallula Gap

Wallula Gap …

The Wallula Gap spans both sides of the Columbia River (Lake Wallula) and is located in southern Washington State, 16 miles south of Pasco, Washington. Upstream of the Wallula Gap is the mouth of the Walla Walla River and Wallula, Washington, home of an early trading post known as Fort Nez Perce. The fort was located at the bend of the Columbia with a view straight down the Gap. Across from the mouth of the Walla Walla at the edge of the Wallula Gap basalts is the former Washington State town of Yellepit, the location of Lewis and Clark’s campsite of April 27 and 28, 1806. At the head of the Wallula Gap lies Port Kelley and Spring Gulch. Lewis and Clark spent the night of October 19, 1805, near Spring Gulch.

“… the river passes into the range of high Countrey at which place the rocks project into the river from the high clifts which is on the Lard. Side about 2/3 of the way across and those of the Stard. Side about the Same distance, the Countrey rises here about 200 feet above The water and is bordered with black rugid rocks …”
[Clark, October 18, 1805]

Wallula Gap National Natural Landmark
The Wallula Gap was designated as a National Natural Landmark in August, 1980.

Wallula Gap Basalts …

The basalts flows of the Wallula Gap were created in the Miocene Era, over 10 million years ago, and are part of the massive fissure flood basalts of the Columbia River Basalt Group (CRBG). Wallula Gap was created when ancestral Columbia and Snake Rivers flowed through a low area of the basalts.

The Creation of Wallula Gap …

From Geologist Bruce Bjornstad of the Pacific Northwest National Laboratory, as presented to the Geological Society of America’s annual meeting in Salt Lake City on October 17, 2005:

“… The story of Wallula Gap begins back in the Miocene Epoch, about 17 million years ago. At that time, lava flows of basalt ran out of giant fissures in the Earth’s crust east of here, near the Idaho-Oregon-Washington border. During basalt volcanism, the southern and western portions of the Columbia Plateau, including Wallula Gap, began to warp and fold under stresses deep in the Earth’s crust. The bending of the ancient lava flows is clearly visible in the folded layers of basalt exposed in the steep walls of the gap.
Early in the history of folding, the ridgecrest here was slightly lower than elsewhere along the ridge. This caused first the ancient Salmon-Clearwater River (precursor to the Snake River), and then the Columbia River to flow across the ridge over this low point. As the ridge continued to bend upward, river erosion kept pace, and a water gap developed. Until about 10 million years ago only the ancestral Salmon-Clearwater River flowed through Wallula Gap. It wasn’t until about 6 million years ago that the Columbia River joined in, where it has continued to flow ever since. Somewhere between 2 and 3 million years ago, the ancestral Salmon-Clearwater River captured the Snake River in the vicinity of Hell’s Canyon, along the Idaho-Oregon border; this added significantly to the amount of water draining through the gap. …”

Wallula Gap and the Missoula Floods …

Wallula Gap is the largest, the most spectacular, and the most significant of the several large water gaps through the basalt anticlines in the Columbia Basin, and funneled the mighty waters of the Missoula Floods. The Missoula floods are the largest known floods on Earth in the last two million years; the flow of water was ten times the combined flow of all the rivers of the world. The flood crest at Wallula Gap on the Columbia River at the Washington-Oregon border was about 1,200 feet, as evidenced by glacial erratics that were left stranded on the slopes of the Horse Heaven Hills and other anticlinal ridges. The water that poured down the Columbia River Gorge stripped away soil, surficial sediments, and talus up to 1,000 feet elevation as far as The Dalles, Oregon . By the time it reached Crown Point, the surface of the last flood (there were over 40 individual floods) had dropped to about 600 feet elevation The average interval between Missoula floods was about 30 years, with the last flood occurring about 13,000 years ago.


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