Historic Earthquakes
Clarkston Valley, Montana
1925 06 28 01:21 UTC (local 06/27)
Magnitude 6.6
Intensity VIII
The most severe damage from this strong earthquake occurred in Gallatin County at Manhattan, Three Forks, Logan, and Lombard. Because no large cities were near the epicenter, property damage did not exceed $150,000.
Community High School at Manhattan, Montana, damaged by the June 28, 1925, earthquake. (Photograph by J.T. Pardee.)
At Manhattan, the community high school and the grade school were both damaged severely, but reinforced concrete buildings were undamaged. Many chimneys were toppled.
At Three Forks, walls of the schoolhouse bulged on all sides, and its foundation and basement were damaged. A church, whose walls were not tied together by an upper floor, also sustained heavy damage. Later shocks demolished the walls. Almost all masonry buildings showed cracks and damage, but because most of the buildings were of frame construction, they sustained only cracks in plaster and some fallen chimneys.
At Logan, the poorly designed and constructed schoolhouse was damaged heavily. However, a large brick roundhouse sustained only a few cracks. As at Three Forks, most of the buildings at Logan were of frame construction and therefore sustained only cracks in plaster and destruction of chimneys.
At Lombard, where the Chicago, Milwaukee and St. Paul Railway crosses the Northern Pacific Railway, large boulders were dislodged to such an extent that trains were delayed on the Northern Pacific line. Also, a huge rock slide blocked the Deer Park entrance of the Lombard Tunnel on the Chicago, Milwaukee and St. Paul Railway and the canyon of Sixteenmile Creek, causing a lake to form.
Cracks occurred in graded and filled roads but not in cuts or where the natural surface had not been disturbed. Approaches to many bridges settled as much as 30 centimeters. One spring formed near Josephine and began to flow, but other springs and sources of water in the neighborhood ceased to flow. Felt from the North Dakota line to Washington, and from southern Canada to southern Wyoming. Aftershocks continued for several months.
Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.
