To see evidence of the Columbia River’s ancient past, you might not need to visit the river at all. In a roadcut just south of Granger, Yakima County, 10 million-year-old evidence is in plain view.
“Geology in Eastern Washington doesn’t get much better than this,” says Nick Zentner — who teaches geology at Central Washington University — as he walks along the shoulder of the road, rock hammer in hand.
Thousands of smooth, round river cobbles embedded in the hillside glitter in the afternoon sun. But there is no longer a river here. Each cobble is made of quartzite, a rare rock for Washington found primarily in the northeast corner of the state, where there was a coastline a billion years ago.
The Columbia River picked up these quartzite rocks and moved them across the region, tumbling and smoothing them along the way.
“This is a snapshot,” Zentner says of the hillside’s cobbles. “Where the Columbia River, more wild than the Columbia River we know, of course, but that white water, that vigorous water, that free-flowing Columbia River is coming right through here.
“And then it left.”
From 10 million to 1 million years ago, the Columbia — in some places a mile wide and 500 feet deep — transported snowmelt from the Rocky Mountains to the ocean. Lava flows repeatedly pushed the river from its path, but the river always found a way around, carving channels and dropping waterfalls over basalt.
Lava floods, ice age floods and the ancestral Columbia River carved the steep canyons and coulees we see in Eastern Washington today. And within just the past 95 years, humans used these natural formations to build dams and harness the power of the river to produce electricity and to irrigate agriculture.
