The Greater Yellowstone Ecosystem - Mountains and Plains: The Ecology of Wyoming Landscapes - page 254

Fig. 15.9. this view of Jackson Hole from the top of Signal
Mountain shows forests of lodgepole pine and subalpine fir
on glacial moraines, and shrublands dominated by mountain

big sagebrush in the foreground and on the glacial outwash
plains. the Gros Ventre Mountains rise to the east beyond the
Snake River. See also fig. 2.6.

ently because of the shallow, infertile, often reddish
soils that have developed there on cretaceous shales.

suggests relatively deep soils having considerable water-
holding capacity. the second type of community, found
farther south near the Jackson airport and Blacktail
Butte, is characterized by an association of mountain
big sagebrush and bitterbrush. the abundant bitter-
brush suggests a higher percentage of sand or gravel in
the soil. the third type of community can be seen west
of the Snake River in the southern part of the valley
and north of Moran. Here the sagebrush community
forms an intriguing mosaic, with patches of low sage-
brush here and there where mountain big sagebrush
predominates (fig. 15.10). Low sagebrush is known to be
an indicator of shallow soils, sometimes with impeded
drainage or low fertility. overall, the sagebrush mosaic
probably reflects different glacial outwash patterns as
well as differences in the rock types found in the moun-
tains to the west and east of the valley. 35

Sagebrush Mosaic

Most of Jackson Hole is an unusually flat sagebrush
steppe, interrupted only by the Snake River valley and
a few buttes and moraines. Geologists refer to the area
as a glacial outwash plain, because it was deposited by
the meltwaters of the mountain glaciers that developed
80,000 to 12,000 years ago. one of the primary effects
of the meltwater was to wash away much of the silt and
clay that would have greatly enhanced the nutrient and
water storage capacity of the soil. Subsequently, how-
ever, this loss was compensated for by windblown loess
deposits from the west, such as from the Snake River
plains of present-day idaho.
close examination of the sagebrush steppe indicates
that at least three types of plant communities are rep-
resented. east of the Snake River, there is a dense cover
of mountain big sagebrush, idaho fescue, and other
species. the abundance of big sagebrush in this area

Gros Ventre Landslide

the mountain ranges to the east of Jackson Hole have
diverse origins—the volcanic Absarokas to the north-