Landscape History - Mountains and Plains: The Ecology of Wyoming Landscapes - page 19

Fig. 2.6 Jenny Lake in Grand teton national Park is contained
by forested terminal and lateral glacial moraines at the base of
cascade canyon. the canyon is a U-shaped valley formed by
glaciers. the forests on the moraines are dominated by lodge-
pole pine, subalpine fir, and engelmann spruce. Douglas-fir
and limber pine are common on the lower slopes of the

tetons; subalpine fir and engelmann spruce are abundant on
the north-facing slopes of the canyon, and whitebark pine is
common in the alpine zone. Shrublands dominated by moun-
tain big sagebrush are found on the glacial outwash plains
below. the highest peak is Grand teton (13,766 feet); the ele-
vation of Jenny Lake is 6,779 feet. Photo by Michael collier.

the mountains during cold periods, often forming drifts
that persisted through the summer. More snow caused
higher reflectivity of solar radiation, lowering the tem-
perature further. Many snow masses were converted to
mountain glaciers. 23 Far to the north, huge continental
glaciers moved southward, forcing the Missouri River
to flow into the Gulf of Mexico rather than into Hud-
son Bay, as it had previously. continental glaciers never
reached Wyoming, but features such as terminal and
lateral moraines, U-shaped mountain valleys, cirques,
glacial outwash plains, and kettle topography indicate
that extensive glaciers were present in most mountain
ranges and on the Yellowstone Plateau (figs. 2.5 and
2.6). the nearest continental glacier was in present-day
northern Montana.
During periods of glaciation, tremendous amounts
of water accumulated in the ice for thousands of years.
Glaciers formed and then thawed during warm periods

about 7 times during the past 750,000 years (50 times
since the mid-Pliocene). With each episode of melting,
widespread flooding shaped broad riparian floodplains,
known as glacial outwash plains. Later these flood-
plains became terraces and benches, such as along the
Snake River in Grand teton national Park and along the
Laramie River in the southeast (see chapter 4).
Huge freshwater lakes also formed, including Lake
Bonneville in Utah, Lake Missoula in southwestern
Montana, and Lake Wamsutter in the Great Divide
Basin of central Wyoming—along with the smaller Fre-
mont, Jackson, and Yellowstone lakes in northwestern
Wyoming. 24 the grinding of rock by moving ice pro-
duced fine glacial dust, which was washed down rivers
and blown into the basins and plains. Deposition of this
material, known as loess (pronounced lüss), contributed
to the development of fertile soils in areas that now
support grasslands and shrublands. As the snow melted