The scene is Utah's Wasatch Range, a mountain range running generally north/south from Utah’s border with Idaho, south into the central portion of the state. The mountains are steep and rugged, with the highest peak reaching 11,928 feet. The elevation in the valleys is about 4,300 feet. 

Like other mountain ranges in the West, the Wasatch is home to a wide variety of game species, including elk. In the Browning trail cam video below, you’ll see a group of elk cows and calves as they feed in a forest opening. Note that one of the cows had been trapped and fitted with a GPS collar. 

The elk show up in front of the trail cam at 7:19 p.m. and for nearly 20 minutes they feed in peace. It’s early July, so the calves are still quite small and have spotted coats. Of course, elk are a prey species and rely heavily on their senses of smell, sight and hearing to avoid predators (two-legged and four-legged), and a couple cows begin to show wariness at 7:38 p.m. At that point, the calves are feeding comfortably. However, 10 minutes later, the entire group is on edge. It appears to me that they smell a predator but can’t pinpoint its location.

Notice how it is dead calm. None of the vegetation is moving, and the trail cam is picking up decent audio of the elk walking, but there’s no wind noise. Big game animals such as elk have more success smelling approaching predators when there’s a steady breeze to carry odors along the ground, but in this case, the elk aren’t getting much help.

The young cow nearest the trail cam finally gets a whiff of a mountain lion and immediately signals to the group with a high-pitched bark to flee, but it’s too late. The cougar instinctively targets a calf, which is slower and smaller than a cow, and you can hear the outcome. It’s just like an e-caller’s “fawn distress” sound file used to lure coyotes and other predators into shooting range.

The person who uploaded this 1-minute video to YouTube said he found the calf's carcass only 15 feet downhill from where the cougar exits the scene.

One final comment: Earlier I talked about the wind conditions on this particular July evening. After the elk flee, watch the dirt that’s been kicked into the air, and pay attention to the direction and speed in which it is carried away. The mountain lion stalked the elk from upwind, which certainly wasn’t ideal, but the near-negligible wind allowed it to get close enough to make its rush.