US Geological Survey

In December of 1872, an earthquake shook the Pacific Northwest so hard that a Seattle resident described watching near-tidal waves roil Lake Union.

And it wasn’t just Seattle; the quake shook from Eugene, Oregon to Canada. It triggered a landslide near Wenatchee that briefly dammed the Columbia River.

For years, geologists couldn't pin down the quake's source. But now they think they've found it: A previously unknown fault near Entiat on the east side of the Cascades.

"So we had this big earthquake but no one could put their finger on where's the fault that's responsible," said Brian Sherrod, a paleoseismologist with the US Geological Survey.

A paleoseismologist studies ancient earthquakes. Sherrod said the source of the massive quake has baffled scientists for decades. Guesses placed the epicenter everywhere from Sedro-Woolley to Lake Chelan to British Columbia.

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A 4.2 earthquake gave a shake to Lewis and Thurston counties just before 8 am this morning. The US Geological Survey reports the small temblor was centered between the town of Morton and Mossyrock.  No injuries or damages have been reported.