Landscape History - Mountains and Plains: The Ecology of Wyoming Landscapes - page 20

each spring, mountain soils were subjected to flushing
by large volumes of water, which eroded soil particles
and slowed the accumulation of nutrients. Soil develop-
ment in the mountains was most rapid where soft rocks
(such as shales) were exposed instead of harder rocks,
like granite, rhyolite, limestone, and some sandstones.
Volcanic activity during this time included enormous
caldera-forming eruptions followed by multiple lava
flows that created much of the topography seen in
Yellowstone national Park today (see chapter 15). 25
though commonly thought of as the ice Age, the
Pleistocene also had extended warm periods, even
warmer than during much of the past 10,000 years. 26
All or most of the ice melted at such times. Present-day
glaciers formed about 400 years ago, during a period
known as the Little ice Age (ca. 1550-1850). they are
now small, confined to high mountain peaks, espe-
cially in the Wind River Mountains, and are now reced-
ing due to climate warming during recent decades (see
chapter 3). 27
At the beginning of the Quaternary, 2.6 million
years ago, the flora of the region was similar to what it
is today. 28 Forests dominated by familiar conifers were
common in the mountains, and shrublands and grass-
lands were common in the basins and on the plains.
cottonwood, aspen, bur oak, boxelder, paper birch, and
Rocky Mountain maple were present, but most other
species of broad-leaved trees, along with redwood and
cypress, have not been found in the fossil record for that
time.

Shoshoni, Sioux, and Ute. 31 By that time the glaciers had
receded into the mountains.
Learning about change during the Holocene—the
past 10,000 years—has been facilitated by the analysis
of fossil pollen and other plant fragments. in wetlands,
these materials settled and were preserved in anaerobic
sediments for thousands of years. 32 Paleoecologists
have learned to identify the kinds of plants from which
the partially preserved pollen, cones, seeds, and leaves
came. Because sediments accumulated with time, the
deeper plant materials usually are older. thus, changes
in plant materials with depth suggest how the vegeta-
tion of the surrounding land area has changed over
thousands of years.
Paleoecological studies in Wyoming and nearby pro-
vide evidence of continued change through the Pleis-
tocene to the present (fig. 2.7). 33 For example, plant
fragments collected from the northern end of the teton
Range document the presence of ponderosa pine about
127,000 years ago, during the last interglacial period,
when the climate was warmer than it is today. this coni-
fer is now absent from that area and the Yellowstone
region. Studies by cathy Whitlock and her students at
Montana State University describe the vegetation his-
tory of this area over the past 30,000 years, during and
following the last glacial period (known as the Pine-
dale). they concluded that ice covered the Yellowstone
region at times during the Pleistocene, 34 when the mean
annual temperature was about 9-18°F lower than it is
today. conifers were restricted to a narrow band in the
foothills, and tundra-like vegetation was widespread
across the lowlands (fig. 2.8). throughout Wyoming's
basins, permafrost was widespread. Several of the preva-
lent mammals at the time are now characteristic of the
Arctic—caribou, collared lemming, and barren-ground
muskox. 35 Mammoth and mastodon roamed the inter-
mountain basins as well.
Whitlock's research indicates that engelmann
spruce was one of the first trees to colonize the areas
vacated by receding glaciers, but within a few centu-
ries it was joined by whitebark pine, subalpine fir, and
lodgepole pine. Such forests were widespread at middle
and high elevations throughout Wyoming until 11,000
years ago, when the climate became warmer and drier.
these conditions led to an upward shift in upper and
lower treelines and the development of lodgepole pine

Thousands of Years Ago

the first people arrived in north America about 15,000
years ago. 29 With their ingenuity, tools, and weapons,
they spread rapidly. their hunting is commonly thought
to have been a primary cause of the extinction of large
mammals, such as the mammoth, giant sloth, camel,
horse, and various other species that existed at the time;
but contributing factors may have been climate warming
and reduced food availability caused by droughts. the
hunters became known as the clovis people. they were
able to kill 10-ton mammoths with their stone-tipped
weapons. 30 clovis descendants eventually organized into
various tribes, including the Apache, Arapahoe, Black-
foot, cheyenne, comanche, crow, Flathead, Kiowa,