relatively flat terrain. The Tetons and other north-central ranges contain folded and faulted rocks of Paleozoic and Mesozoic age draped above cores of Proterozoic and Archean igneous and metamorphic rocks ranging in age from 1.2 billion (e.g., Tetons) to more than 3.3 billion years (Beartooth Mountains). Ecology and climate There are a wide range of environmental factors in the Rocky Mountains. The Rockies range in latitude between the Liard River in British Columbia (at 59° N) and the Rio Grande in New Mexico (at 35° N). Prairie occurs at or below , while the highest peak in the range is Mount Elbert at . Precipitation ranges from per year in the southern valleys to per year locally in the northern peaks. Average January temperatures can range from in Prince George, British Columbia, to in Trinidad, Colorado. Therefore, there is not a single monolithic ecosystem for the entire Rocky Mountain Range. Instead, ecologists divide the Rockies into a number of biotic zones. Each zone is defined by whether it can support trees and the presence of one or more indicator species. Two zones that do not support trees are the Plains and the Alpine tundra. The Great Plains lie to the east of the Rockies and is characterized by prairie grasses (below roughly ). Alpine tundra occurs in regions above the tree-line for the Rocky Mountains, which varies from in New Mexico to at the northern end of the Rockies (near the Yukon). The U.S. Geological Survey defines ten forested zones in the Rockies. Zones in more southern, warmer, or drier areas are defined by the presence of pinyon pines/junipers, ponderosa pines, or oaks mixed with pines. In more northern, colder, or wetter areas, zones are defined by Douglas firs, Cascadian species (such as western hemlock), lodgepole pines/quaking aspens, or firs mixed with spruce. Near tree-line, zones can consist of white pines (such as whitebark pine or bristlecone pine); or a mixture of white pine, fir, and spruce that appear as shrub-like krummholz. Finally, rivers and canyons can create a unique forest zone in more arid parts of the mountain range. The Rocky Mountains are an important habitat for a great deal of well-known wildlife, such as wolves, elk, moose, mule and white-tailed deer, pronghorn, mountain goats, bighorn sheep, badgers, black bears, grizzly bears, coyotes, lynxes, cougars, and wolverines. North America's largest herds of moose are in the Alberta–British Columbia foothills