The Dall Sheep, is a species of sheep native to northwestern North America, ranging from white to slate brown in color and having curved yellowish brown horns. There are two putative subspecies: the northern Dall Sheep proper (Ovis dalli dalli) which is almost pure white, and the more southern Stone Sheep (also spelled Stone's Sheep) (Ovis dalli stonei), which is a slaty brown with some white patches on the rump and inside the hind legs.
Research has shown that the use of these subspecies designations is questionable. Complete colour integradation occurs between white and dark morphs of the species with intermediately coloured populations, called Fannin's Sheep (Ovis dalli fannini), found in the Pelly Mountains and Ogilvie Mountains of Yukon Territory. Mitochondrial DNA evidence has shown no molecular division along current subspecies boundaries, although evidence from nuclear DNA may provide some support. Also at the species level current taxonomy is questionable because hybrdization between Ovis dalli and Ovis canadensis has been recorded in recent evolutionary history.