July 28, 2009; North Entrance;Yellowstone National Park.

From Wikipedia:
The bighorn sheep (Ovis canadensis)[3] is a species of sheep in North America[4] named for its large horns. These horns can weigh up to 30 pounds (14 kg), while the sheep themselves weigh up to 300 pounds (140 kg).[5] Recent genetic testing indicates that there are three distinct subspecies of Ovis canadensis, one of which is endangered: Ovis canadensis 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. However, by 1900 the population had crashed to several thousand. Conservation efforts (in part by the Boy Scouts) have restored the population.

Bighorn sheep are named for the large, curved horns borne by the rams (males). Ewes (females) also have horns, but they are shorter with less curvature.[14] They range in color from light brown to grayish or dark, chocolate brown, with a white rump and lining on the back of all four legs. Males typically weigh 127?316 pounds (58?143 kg), are 36?41 inches (91?100 cm) tall at the shoulder, and 69?79 inches (180?200 cm) long from the nose to the tail. Females are typically 75?188 pounds (34?85 kg), 30?36 inches (76?91 cm) tall and 54?67 inches (140?170 cm) long.[15] Male bighorn sheep have large horn cores, enlarged cornual and frontal sinuses and internal bony septa. These adaptations serve to protect the brain by absorbing the impact of clashes.[16] Bighorn sheep have preorbital glands on the anterior corner of each eye, inguinal glands in the groin and pedal glands on each foot. Secretions from these glands may support dominance behaviors.[16]
Bighorns from the Rocky Mountains are relatively large, with males that occasionally exceed 500 lb (230 kg) and females that exceed 200 lb (90 kg). In contrast, Sierra Nevada Bighorn males weigh up to only 200 lb (90 kg) and females to 140 lb (60 kg). Males' horns can weigh up to 30 lb (14 kg), as much as the rest of the bones in the male's body.[17]