Earthquakes

The sign's figures were early ones. Later measurements put the mountain's rise at about a foot rather than six inches and the valley's drop at up to eight feet, along a fresh scarp more than twenty miles long. The shaking reached far beyond this valley. It was felt in eight western states and in Canada, it shut down a nuclear test reactor on the plain to the southeast, groundwater flows shifted for hundreds of miles, and a butte near Mackay began spouting water until some feared the reservoir below it would overfill.

What the plaque says

Earthquakes On October 28, 1983, a major earthquake fracture, 26 miles long and 7 miles deep, surfaced as Lost River Valley slid away from Mount Borah. During that rock shift, Mount Borah's ridge front rose about 6 inches, while this valley subsided 9 feet. This kind of movement has been going on here for 10 to 20 million years as subsurface rock has been pulled apart during gradual but persistent range and valley building. You can drive to a spectacular fracture that shattered this side road 2-1/2 miles from here. 356 Text prepared by the Idaho Historical Society Marker made & installed by Idaho Transportation Department

Where it stands

Worth the stop nearby

• Borah Peak Earthquake Fault Scarp — 2.5 mi
  In 1983 the valley floor dropped seven feet in a second, and a truckload of hunters dropped with it.

More markers nearby

• Mount Borah — steps away
• Goddin's River — 12 mi
• Mount McCaleb — 21 mi
• Ghost Towns of Mackay, Idaho — 21 mi