Bull bison spend hours horning trees, particularly during the summer rut, their mating season. Biologists have observed that this horning, which eventually kills many trees, is a major mechanism for maintaining the open sagebrush grassland edge of the Hayden Valley. But for the battering trees would expand in time take over much of the valley. The injured trees exude resin which in the low light of the afternoon recall some of the hues of amber.

Here a column of buffalo has passed through. Each animal follows the one in front stepping into the post holes of the one that has gone before, thus minimizing the amount of energy required to move through the deep snow. In this case a coyote has chosen to travel on the floor of the trench between the post holes…coyotes are infallible in interpreting the energy saving nuances of snow in these matters.