National Geographic : 1904 Sep
Turtle Mountain and the Great Rock-slide at Frank, Alta, Looking Northward At dawn on April 29, 1903, a huge rock mass, nearly half a mile square and probably 400 to 500 feet thick inplaces, suddenly broke loose from the east face of Turtle Mountain and precipitated itself with terrific violence into the valley beneath, overwhelming everything inits course. The great mass, urged forward by the momentum acquired in its descent and broken intoinnumerable fragments, plowed through the bed of Old Man River, and, carrying both water and underlying sediments along with it, crossed thevalley and hurled itself against and up the opposite terraced slopes to a height of 400 feet. Blocks of limestones and shale, mingled with mud,now cover thevalley toadepth offrom 3to probably 150 feet, over an area of 1.03 square miles. A rough estimate of the size of the mass whichbroke away, obtained bycomparison ofthe old and new contours of the mountain itself, is about 40,702,000 cubic yards, or 90,796,000 tons. TheFrank slide was a"Bergsturz," abreaking away of the mountain mass across the bedding planes. The cavity left by the breaking away of thecentral peak and the course oftheslide can be distinctly seen. Under the slide-rock the terraced floor of the valley is discernible. The uneven, billowed surface oftheslide-rock iswell shown, and the heaped-up rim along the edges of the slide can be seen at several points. In the foreground isathin promontory ofdebris de flected from the main course of the slide. The town lies on the farther side of the slide in the direction ofthegap between themountains. A special report on this great slide has been recently published by the Department of Interior, at Ottawa.