Geologists may be close to cracking one of the biggest seismological mysteries in the Pacific Northwest: the origin of a powerful earthquake that rattled seven states and provinces when Ulysses S. Grant was president.

Preliminary evidence points to a newly discovered fault near the town of Entiat in Chelan County, Wash. The find adds to a growing body of evidence that Central and Eastern Washington are more quake-prone than previously thought, and will help refine seismic risks in an area that's home to 1.5 million people, more than a dozen hydropower dams and the Hanford nuclear reservation, said Craig Weaver, regional chief of the U.S. Geological Survey's earthquake programs.

"For more than four decades, people have been guessing where the 1872 earthquake was," Weaver said. "To be able to finally pinpoint this thing on a map would be really important in helping us get the seismic hazard assessment correct in that part of the state."