In
western North America, the Rocky Mountains rise to snow-capped
peaks. In this environment, life changes with elevation.
Lichens and grasses are found near the mountain summits.
Below the timberline, evergreen forests of spruce, fir,
and pine clad the slopes. Mule deer and elk winter at
lower levels, moving higher in the summer. Pumas and
eagles range widely in search of food.
In Native American
times, the American Midwest was a vast expanse of grassland
hosting millions of bison and pronghorns, miles of prairie
dog towns, innumerable small mammals, and predators such
as the coyote and wolf. From the Rockies eastward, the
land gradually slopes downward toward the Mississippi.
Short grasses of the high western plains merge with the
tall grasses of the prairie lowlands to the east.