Earthquake Lake

On August 17, 1959, the largest earthquake recorded in Montana, with a magnitude of 7.3 on the Richter scale, rocked the Madison River Canyon. Earthquake Lake was formed when a giant landslide, triggered by the earthquake, blocked the Madison River. The landslide can be seen behind the lake in this close-up. As the lake level rose, the trees around the rim of the lake were drowned. This earthquake also resulted in the disturbance of the groundwater piping in geysers at adjacent Yellowstone National Park, including a slight change in the eruption periodicity of the Old Faithful Geyser from 61 minutes to 65 minutes. Other geysers sprang to life and bubbling springs erupted violently.

Print No. A01NW-35-8

Madison River Canyon Earthquake Scarp

The scarp of the Madison River Canyon Earthquake is prominent here in Red Canyon, north of Hebgen (Earthquake) Lake. The scarp has a maximum vertical displacement of 21 feet (almost 7 meters) and runs about 14 miles (23 Km).

Print No. A01NW-35-10

Boulder Batholith

Boulder Batholith lies between Helena and the Highland Mountains south of Butte and consists of mostly granite of Cretaceous age. When the batholith formed about 75 million years ago, the heat of the magma caused the overlying groundwater to dissolve gold, silver, copper, and other elements and minerals. The circulation of the groundwater cooled the granite, precipitating metallic ores in some adjacent sedimentary and metamorphic rocks the granite intruded into, producing veins of precious metals.

Print No. A01NW-31-3