Few animals are so well adapted to extremes of elevation and temperature as the magnificent wild sheep of western North America’’s mountains. Their range extends from the Brooks Range of northern Alaska, where Dall sheep live, to the Desert Bighorn sheep of Death Valley, California. The wild, or mountain sheep is a stocky, hoofed mammal. The front hoofs of mountain sheep are slightly larger than the hind, but both leave a print, which is almost rectangular. A hard rim around the outer edge of each hoof surrounds a softer, concave area in the middle, giving excellent traction on rocky terrain. The most distinctive characteristic of the males is their massive horns, which spiral in an arc, making a full curl on a mature ram. Adult females have slightly curved horns about a foot long or less and can sometimes be mistaken for mountain goats, although their range rarely overlaps.

North American wild sheep are related both to domestic sheep (Ovis aries), which were imported from Europe by early settlers, and to the native sheep of Asia. It is thought that about half a million years ago a primitive sheep similar to the present-day Marco Polo sheep of Central Asia migrated into North America via the Bering land bridge, which formerly connected Russia and Alaska. When the glaciers of the ice age expanded south from their polar centers those animals became isolated in two ice-free areas, or refugia, one in central Alaska and the other south of the Columbia and Snake Rivers, in the lower 48. Sheep in the Alaska refugium evolved into the slender-horned Dall sheep (Ovis dalli), those farther south evolved into the heavy-horned Rocky Mountain and Desert bighorns (Ovis canadensis). As the ice sheet retreated 10 to 20 thousand years ago, the northern sheep expanded their range east to the Mackenzie Mountains and south to the Peace River of northern British Columbia.

Gradually two subspecies, or races, evolved. The white Dall sheep, which now ranges across Alaska (excluding Southeast) into the Yukon Territory and the western edge of Mackenzie District. The darker cousin of the Dall sheep is the Stone sheep, which makes its home in northern British Columbia and southern Yukon. Driving up the Alaska Highway one often can see Stone sheep near Stone Mountain in British Columbia and some of them appear so dark they nearly look black. In the Pelly Mountain area of the Yukon, black and white Dall sheep merge gradually with each other. The curious result, known as the Fannin, or saddle-backed sheep, has a white head, neck, and rump, but a gray body.

Mountain sheep are very agile, being second only to mountain goats in the steepness of terrain they can climb. However, the goat is more of a climber or walker, while the sheep, which bounds like a mule deer, can move much faster.

There were probably over one million bighorns in North America at the start of the 19th Century. A tremendous decline occurred from 1850 to 1900 as a result of diseases introduced by domestic sheep, loss of ranges to livestock, and excessive hunting by man. Luckily, the northern populations of Dall sheep and Stone sheep have not changed as much since much of their range has not been permanently settled or altered by man.