Okotoks Erratic (also known as either Big Rock or, in

Blackfoot The Blackfoot Confederacy, ''Niitsitapi'', or ''Siksikaitsitapi'' (ᖹᐟᒧᐧᒣᑯ, meaning "the people" or " Blackfoot-speaking real people"), is a historic collective name for linguistically related groups that make up the Blackfoot or Bl ...

, as Okotok) is a 16,500-tonne (18,200-ton)

boulder In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In ...

that lies on the otherwise flat, relatively featureless, surface of the

Canadian Prairies The Canadian Prairies (usually referred to as simply the Prairies in Canada) is a region in Western Canada. It includes the Canadian portion of the Great Plains and the Prairie provinces, namely Alberta, Saskatchewan, and Manitoba. These provin ...

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

. It is part of the Foothills Erratics Train of typically angular boulders of distinctive

quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...

and pebbly quartzite. This massive angular boulder, which is broken into two main pieces, measures about and is high. It consists of thick-bedded,

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

ceous,

feldspathic Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocla ...

quartzite that is light grey, pink, to purplish. Besides having been extensively fractured by frost action, it is unweathered. Big Rock lies about west of the town of

Okotoks Okotoks ( , originally ) is a town in the Calgary Metropolitan Region, Calgary Region of Alberta, Canada. It is on the Sheep River, approximately south of Downtown Calgary. Okotoks has emerged as a bedroom community of Calgary. According to t ...

, Canada, south of Calgary in the SE. 1/4 of Sec. 21, Township 20, Range 1, West 5th Meridian.Stalker, A MacS (1975). "The big rock." In Structural geology of the foothills between Savanna Creek and Panther River, S.W. Alberta, Canada. May 23, 1975. H. J. Evers and J. E. Thorpe, eds., pp. 9-11. Calgary, Alberta, Canada: Canadian Society of Petroleum Geologists.Cruden, DM, W Langenberg, and RC Paulen (2003). ''Geology of the Frank Slide and southwestern Alberta. Edmonton Geological Society – Geological Association of Canada annual field trip celebrating the 100th anniversary of the Frank Slide Disaster.'' Edmonton, Alberta: Edmonton Geological Society. 34 pp. Big Rock is a

glacial erratic A glacial erratic is a glacially deposited rock (geology), rock differing from the type of country rock (geology), rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by gla ...

that is part of a long, narrow ( wide), linear scatter of thousands of distinctive

and pebbly quartzite glacial erratics between and in length. This linear scatter of distinctive quartzite glacial erratics is known as the Foothills Erratics Train. The Foothills Erratics Train extends along the eastern flanks of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

of Alberta and northern

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

to the International Border. The boulders and smaller gravel, which comprises the Foothills Erratics Train, consist of Lower

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

shallow marine quartzite and conglomeratic quartzite, which occurs only within the

Gog Group The Gog Group is a stratigraphic unit in the Western Canada Sedimentary Basin. It is present in the eastern and western main ranges of the Canadian Rockies in Alberta and British Columbia.Desjardins, P.R., Buatois, L.A., Pratt, B.E. and Mágano, ...

and is found in the

Athabasca River The Athabasca River (French: ''Rivière Athabasca'') in Alberta, Canada, originates at the Columbia Icefield in Jasper National Park and flows more than before emptying into Lake Athabasca. Much of the land along its banks is protected in nationa ...

Valley of central western Alberta. Big Rock is the largest erratic within the Foothills Erratics Train. Lying on prairie to the east of the Rocky Mountains and like all the larger erratics, it is visible for a considerable distance across the prairie and served as a prominent landmark for Indigenous people.Stalker, A MacS (1956). "The erratics train, Foothills of Alberta." Geological Survey of Canada, Bulletin no. 37, 28 p.

Geologic history

Near the end of the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

Period, between 12,000 and 17,000 years ago, a massive landslide occurred within the upper reaches of the Athabasca River valley. As a result of this landslide, millions of tonnes of beige to pinkish quartzite and quartzitic conglomerate slid from the side of a mountain and onto the top of a valley glacier within the Athabasca River valley. On its top, the narrow valley glacier carried eastward this mass of Gog Group quartzite and quartzitic conglomerate. Because it lay on and within the top of this glacier, the highly fractured boulders were neither broken up into smaller blocks nor rounded by movement of the glaciers that transported it. After leaving the Rocky Mountains, the valley glacier collided with the westward moving ice streams of the Laurentide Ice Sheet and both it, other Rocky Mountain valley glaciers, and Laurentide ice streams coalesced as ice streams and were diverted southward and parallel to the eastern flanks of the Rocky Mountains. Together they flowed as far south as northern Montana as an ice sheet before they stagnated and melted. When the ice sheet melted, erratics of Gog quartzite and quartzitic conglomerate were dropped to form the line of rocks known as the Foothills Erratics Train. Big Rock is one of these glacial erratics of Gog quartzite and quartzitic conglomerate that originated as part of a landslide in the Athabasca River valley and carried on the top of a glacier, later ice stream, to its present site.

History

The people of the

First Nation used Big Rock as a landmark for finding a crossing over the

Sheep River The Sheep River is located in southwestern Alberta, Canada, and is part of the Bow River watershed. The river begins in the mountain valleys of Elbow-Sheep Wildland Provincial Park,Blackfoot language The Blackfoot language, also called Niitsi'powahsin () or Siksiká ( ; , ), is an Algonquian languages, Algonquian language spoken by the Blackfoot Confederacy, Blackfoot or people, who currently live in the northwestern plains of North Americ ...

, and may refer to the rock.Town of Okotoks - Okotoks' Beginnings
Retrieved 2012-02-09 The rock also contains native pictographs and was considered a medicine rock to the natives. In the 1970s the government declared it a Provincial Historic Site to protect its geological and cultural importance.

James Hector Sir James Hector (16 March 1834 – 6 November 1907) was a Scottish-New Zealand geologist, naturalist, and surgeon who accompanied the Palliser Expedition as a surgeon and geologist. He went on to have a lengthy career as a government employed ...

, a geologist with the Palliser Expedition, first documented the rock in 1863. He misidentified the feature as a

klippe 350px, Schematic overview of a thrust system. The shaded material is called a window or fenster. The klippe is the isolated block of the nappe overlying autochthonous material. A klippe ( German for cliff">German language">German for cliff or c ...

Indigenous perspective

One interesting feature of Big Rock is the large split down the middle. A Blackfoot story describes how this may have happened: One hot summer day, Napi, the supernatural trickster of the Blackfoot peoples, rested on the rock because the day was warm and he was tired. He spread his robe on the rock, telling the rock to keep the robe in return for letting Napi rest there. Suddenly, the weather changed and Napi became cold as the wind whistled and the rain fell. Napi asked the rock to return his robe, but the rock refused. Napi got mad and just took the clothing. As he strolled away, he heard a loud noise and turning, he saw the rock was rolling after him. Napi ran for his life. The deer, the bison and the pronghorn were Napi's friends, and they tried to stop the rock by running in front of it. The rock rolled over them. Napi's last chance was to call on the bats for help. Fortunately, they did better than their hoofed neighbours, and by diving at the rock and colliding with it, one of them finally hit the rock just right and it broke into two pieces. Not only does this story explain why the rock is in two pieces, but also why bats have squashed-looking faces. The tale provides helpful caution against taking back what you have given away. Retrieved 2016-02-11

Present day

Although it has been claimed to be the largest glacial erratic in the world, e.g. Sterenberg (2013),Sterenberg, G., 2013. ''Learning Indigenous and Western mathematics from place.'' ''Mathematics Education Research Journal'', 25(1), pp.91-108. Big Rock is not. For example, one large glacial erratic in Germany measures and is thick.Shroder, J. F. (2011). ''Landforms of Glacial Transportation.'' In ''Encyclopedia of Snow, Ice and Glaciers, Encyclopedia of Earth Sciences Series.'' V. P. Singh, P. Singh, and U. K. Haritashya, eds., pp. 693-694. Springer, AA Dordrecht, The Netherlands, 1254 pages Near Cooking Lake, Alberta, one of several large glacial erratics, which is called the ''Cooking Lake (Number 6) megablock'', covers an area of at least , has a length of and is about thick. Pollen studies indicate that the Lower

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

sedimentary strata that comprise this glacial erratic were transported a minimum distance of about .Stalker, A MacS (1976). "Megablocks, or the enormous erratics of the Albertan prairies." Paper no. 76-1C, pp. 185-188. Ottawa, Ontario: Geological Survey of Canada. Big Rock is located along the side of

Highway 7 The following highways are numbered 7. For roads numbered A7, see list of A7 roads. Route 7, or Highway 7, may refer to: International * AH7, Asian Highway 7 * European route E07 * European route E007 Afghanistan *Kunduz-Khomri Highway (A7) ...

, and public parking is available at the turn-off. Despite the presence of a fence around Big Rock and a sign telling people not to climb, many tourists, who visit the rock, ignore the warnings to either

or climb the tall erratic.Brink, J.W., 2014. ''Managing Chaos: Vandalism and Rock-Art at the Okotoks Erratic, Alberta, Canada.'' In ''Open-Air Rock-Art Conservation and Management: State of the Art and Future Perspectives'', edited by Timothy Darvill and António Pedro Batarda Fernandes, pp. 174–188. Routledge, New York.

In popular culture

Big Rock Brewery in Calgary is named after Big Rock.Patterson, M., and N. Hoalst-Pullen (2014) "The Geography of Beer: Regions, Environment, and Societies." New York, New York: Springer Dordrecht.

References

External links

*Brink, J. (2014
''Okotoks Big Rock – Managing Vandalism with Technology''
Aboriginal Heritage Section, Alberta's history
Retroactive
Alberta Government (June 17, 2014). {{Continental Glaciations Landforms of Alberta Glacial erratics of Canada Foothills County Okotoks Provincial historic sites of Alberta Provincial Historic Resources of Alberta Quartzite formations Individual rocks