Bighorn sheep

The bighorn sheep (Ovis canadensis) is a species of sheep native to North America named for its large horns. These horns can weigh up to 30 lb (14 kg), while the sheep themselves weigh up to 300 lb (140 kg). Recent genetic testing indicates three distinct subspecies of Ovis canadensis, one of which is endangered: O. c. sierrae. Sheep originally crossed to North America over the Bering land bridge from Siberia: the population in North America peaked in the millions, and the bighorn sheep entered into the mythology of Native Americans. By 1900, the population had crashed to several thousand, due to diseases introduced through European livestock and overhunting. Conservation efforts (in part by the Boy Scouts) have restored the population.

Taxonomy and genetics

Ovis canadensis is one of three species of mountain sheep in North America and Siberia; the other two species being Ovis dalli, which includes Dall sheep and Stone's sheep, and the Siberian snow sheep, Ovis nivicola. Wild sheep crossed the Bering land bridge from Siberia into Alaska during the Pleistocene (about 750,000 years ago) and subsequently spread through western North America as far south as Baja California and northwestern mainland Mexico. Divergence from their closest Asian ancestor (snow sheep) occurred about 600,000 years ago. In North America, wild sheep diverged into two extant species—Dall sheep, which occupy Alaska and northwestern Canada, and bighorn sheep, which range from southern Canada to Mexico. However, the status of these species is questionable given that hybridization has occurred between them in their recent evolutionary history.

National Geographic

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Bam Bam

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Rocky Mountains

The Rocky Mountains, commonly known as the Rockies, are a major mountain range in western North America. The Rocky Mountains stretch more than 3,000 miles (4,800 km) from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States. Within the North American Cordillera, the Rockies are somewhat distinct from the Pacific Coast Ranges and the Cascade Range and Sierra Nevada which all lie further to the west.

The Rocky Mountains were initially formed from 80 million to 55 million years ago during the Laramide orogeny, in which a number of plates began to slide underneath the North American plate. The angle of subduction was shallow, resulting in a broad belt of mountains running down western North America. Since then, further tectonic activity and erosion by glaciers have sculpted the Rockies into dramatic peaks and valleys. At the end of the last ice age, humans started to inhabit the mountain range. After Europeans, such as Sir Alexander Mackenzie and Americans, such as the Lewis and Clark expedition, started to explore the range, minerals and furs drove the initial economic exploitation of the mountains, although the range itself never became densely populated.