Twin Sister Pillars
Ice age glacial dams collapsed time after time and sent walls of water down the Columbia River to gouge and chisel the landscape. Where the river makes its great bend north from Oregon into the heart of eastern Washington, the Horse Heaven Hills clamp tight upon the river to form Wallula Gap.
It is here that glacial floods were held back to create a vast temporary backwater that geologist call Lake Wallula. The water rose 1,200 feet high behind the Horse Heaven Hills. As it squeezed and spouted through Wallula Gap the debris-laden glacial flood sculpted the layers of volcanic rock. Twin Sisters are striking evidence of the successive floods that molded this landscape where we followed today on the route of Lewis and Clark.
It was here on Oct. 18, 1805, that the expedition first sighted a known geographic feature since leaving Fort Mandan on the Missouri River. Capt. Clark climbed above Wallula Gap and looking afar saw a great peak that was on a British Naval chart of the lower 100 miles of the Columbia River. President Jefferson sent that chart with the expedition. Clark noted in his journal, “Saw a mountain bearing S.W. Conical Form Covered with Snow.”
The captains determined the peak was Mt. St. Helens in the Cascade Range. It was named in 1792 by Capt. George Vancouver’s naval exploring expedition which came100 miles up the Columbia from its mouth.
Historians and cartographers now believe Clark saw Mt. Hood, the highest peak in Oregon, rather than nearby Mt. St. Helens, but with this sighting the captains took heart in knowing they were approaching the Pacific Ocean. One month later they were camped near the entrance to the mighty River of the West.
Ice age glacial dams collapsed time after time and sent walls of water down the Columbia River to gouge and chisel the landscape. Where the river makes its great bend north from Oregon into the heart of eastern Washington, the Horse Heaven Hills clamp tight upon the river to form Wallula Gap.
It is here that glacial floods were held back to create a vast temporary backwater that geologist call Lake Wallula. The water rose 1,200 feet high behind the Horse Heaven Hills. As it squeezed and spouted through Wallula Gap the debris-laden glacial flood sculpted the layers of volcanic rock. Twin Sisters are striking evidence of the successive floods that molded this landscape where we followed today on the route of Lewis and Clark.
It was here on Oct. 18, 1805, that the expedition first sighted a known geographic feature since leaving Fort Mandan on the Missouri River. Capt. Clark climbed above Wallula Gap and looking afar saw a great peak that was on a British Naval chart of the lower 100 miles of the Columbia River. President Jefferson sent that chart with the expedition. Clark noted in his journal, “Saw a mountain bearing S.W. Conical Form Covered with Snow.”
The captains determined the peak was Mt. St. Helens in the Cascade Range. It was named in 1792 by Capt. George Vancouver’s naval exploring expedition which came100 miles up the Columbia from its mouth.
Historians and cartographers now believe Clark saw Mt. Hood, the highest peak in Oregon, rather than nearby Mt. St. Helens, but with this sighting the captains took heart in knowing they were approaching the Pacific Ocean. One month later they were camped near the entrance to the mighty River of the West.
