Scientists have known that a magnitude 9.0 quake hit off the Washington coast in January of 1700, but until recently they didn't know exactly when.
It became a detective story where geologists in Washington found evidence in soil samples and ghost forests of red cedar trees that the land dropped five feet.
"That's what killed these trees here was the tide water that came in after the earthquake," said geologist Brian Atwater.
And there are records found in Japan of a ghost tsunami, but there was never an earthquake recorded in Japan or Asia at the time.
"And the two eventually came together to eventually give the earthquake time here of the evening of the 26th of January 1700," he said.
Scientists reverse-engineered the tsunami wave that came from the 600-mile long Cascadia subduction zone and figured out the massive shaker started at 9 p.m., 311 years ago today.