This was one of four female bighorns that we found foraging in Yellowstone’s Lamar Valley, which in the spring is known as “America’s Serengeti.” Within eyesight at the time were not only these bighorns, a rare sight at such close range, but also bison, pronghorn, and elk. Meanwhile, just down the road, two black bears grazed in a field. I made numerous images of these bighorn sheep as they worked their way down a slope towards us. This was the shot I was waiting for – it represents the instant one of them dared to cross the diagonal highway boundary separating the world of nature from the world of man.