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Key Number: HS 32420
Site Name: The Big Rock, Erratic
Other Names:
Site Type: 1911 - Geological Feature


ATS Legal Description:
Twp Rge Mer
20 1 5

Address: Highway 7
Number: N/A
Street: N/A
Avenue: N/A
Near Town:


Type Number Date View


Plan Shape:
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Exterior: N/A
Interior: N/A
Environment: Located on Highway 7 midway between Okotoks and Black Diamond, north of road. Site is marked with a provincial sign explaining the source of the rock. The Big Rock sits about 150 yards north of Highway 7, six miles east of Black Diamond and is marked by a large interpretive sign.
Condition: As a major tourist attraction in the area, it is suffering from the usual visitor-related problems of vandalism and litter.
Alterations: N/A


Construction: Construction Date:
Usage: Usage Date:

Owner: Owner Date:
Ronald Sydney Price
David Ronald Price
Architect: N/A
Builder: N/A
Craftsman: N/A
History: The Big Rock is a glacial erratic; a piece of palaeozoic quartzite carried by the glaciers from the vicinity of Mount Edith Cavell on the Athabasca River south of Jasper and was left with the melting of the Pliestocene Glacier 10,000 years ago. This erratic was left in a line with others along the eastern slopes of the rockies marking where the continential ice sheet from the north met the alpine glaciers of the rockies. Indians were taught the Big Rock was there because of the treachery of Napi; the foremost of blackfoot mythical figures. Some accounts say 'okatoks' is blackfoot for 'near the big rock'.
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One of the largest glacial erratics in North America. Marks appriximate Eastward extent of Cordilleran ice sheet in region.
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The Okotoks erratic is an example of the rock debris that has been torn up by the movement of glaciers, transported and redeposited when the glacier reteats. Approximately 70,000 years ago, during the Quaternary Era, glaciers began forming in the mountains and with time, moving out onto the plains. This cordilleron glacier brought great quantities of quartzite and limestone debris with it. The Okotoks erratic, weighing about 18,000 tons is probably the largest erractic in Canada. The Indians attributed great significance to this slab of rock. Legends mention it and pitgraphs have been marked on its surface.
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Geological Significance : The Okotoks erratic is Alberta's best known example of a glacial erratic (illustrated - 1977 Alberta Treasury Branch calendar). Its imposing size and its prominent position in a cultivated field near a major highway has resulted in the erratic receiving several hundred visitors a year. The Big Rock is the largest member of the Foothills Erratics Train and has been reported to be the largest glacial erratic in North America. The Foothills Erratics Train is of scientific value in the interpretation of the interaction of Cordilleran (mountain) and Keewatin (continental) ice masses, and the subsequent development of a late Pleistocene chronology. The name of the nearby town of Okotoks is derived from the Blackfoot word 'okatok' meaning 'big rock'. The erratic is also of archaeological interest as it has a number of Indian pictographs located on its surface which have been described and illustrated in several scientific papers.
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Site Description : The Big Rock sits about 150 yards north of Highway 7, six miles east of Black Diamond and is marked by a large interpretive sign. The erratic consist of two very large boulders that were originally deposited as a single block, having the dimensions 135' x 60' x 30', and weghing an estimated 18,000 tons. The lithology varies from a fine pebble conglomerate to a bedded quartzite. The rock is very hard but is susceptible to splitting along joints and thin silt partings.
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This enormous quartizite block, weighing about 16,500 tonnes and measuring about 41 x 8 x 9 metres, was carried here on the surface of a glacier. It came from the Rocky Mountains in the Jasper area, probably between 18 to 10 thousand years ago. Rocks moved many kilometres from their original location by the ice are called 'glacial erratics'. The Big Rock began its journey when rockslides in the mountains deposited quartzite debris onto the top of a glacier in the Athabasca River valley. The glacier carried the rocks with it as it flowed slowly eastward to the plains, until it collided with the Laurentide ice sheet. This massive ice sheet deflected the glacier to the southeast, parallel to the mountain front. When the ice melted, a string of erratics was left in a narrow belt extending from Jasper National Park along the foothills to northern Montana. This group is known as the Foothills Erratics Train, and the Okotoks Erratic is the largest member. The name of the Rock was derived from the Blackfoot word for rock: okatok. 26 November 1992.


Status: Status Date:

Designation Status: Designation Date:
Provincial Historic Resource
Register: N/A
Record Information: Record Information Date:
K. Williams 1989/08/04


Alberta Register of Historic Places: 4665-0081
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