places in the West, Rabbit ears Pass experienced a decline in Engelmann spruce (Picea engelmannii) trees due to episodic outbreaks of the spruce bark beetle (Dendroctonus rufipennis). During the 1940s much of the subalpine zone of Northwest Colorado was severely affected by beetle outbreak. Spruce beetle outbreaks have taken place in this area in 1716-1750, 1827-1845, 1860-1870, and 1940-1960. Large-scale outbreaks of spruce beetle have long been an important component of the dynamics of subalpine forests in Colorado. During outbreaks, spruce beetle may attack and kill lodgepole pine (Pinus contorta) as well as spruce. Nearly all attacked trees are killed This pass offers habitat to many different animal species. It supports important winter and summering ranges for many animals. Species commonly seen on the pass range from elk, mule deer, and moose, to black bears, foxes, long-tailed weasels, snowshoe hares, and a variety of bird species. The winter snowpack provides a seasonal habitat for many non-hibernating burrowing animals such as voles, lemmings, and shrews. The snowpack helps to make a subnivean zone, which is a porous material composed mostly of air acting as a reliable thermal insulator. Although lower in elevation than many of the high mountain passes farther to the south in the Colorado Rockies, Rabbit Ears Pass often receives a great deal of snow in winter and is subject to regular short closures during heavy winter storms. The seasonal snowpack on this pass is a major source of water for residence in the nearby area. Rabbit Ears pass is a place for many different outdoor recreational activities. In the winter, it is a popular spot for back country snowboarding and skiing, cross-country skiing, and snowshoeing. There are boundaries set up to separate motorized use from foot traffic. These established boundaries decrease conflicts between users and seasonal closures related to snow depth and animal wintering ranges. Non-motorized recreation is permitted west of the pass and motorized recreation is permitted east of the pass. The boundary designating winter recreational usage on Rabbit Ears Pass provides an opportunity to study the influence of motorized recreation on the physical properties of the snowpack and animal use. The United States Department of Agriculture (USDA) Forest Service managing the Routt National Forest has not only implemented boundary regulations, but they have also put into effect regulatory practices designating the start of the snowmobile season when the unpacked snow depth equals or exceeds 30 cm