Sand Dunes, Badlands, Mud Springs, and Mima Mounds - Mountains and Plains: The Ecology of Wyoming Landscapes - page 142

Chapter 9 Sand Dunes,
Badlands, Mud Springs,
and Mima Mounds

Sand Dunes and the power of water and wind to sort and move the

resulting particles. the sand grains (0.05-2.00 mm in
diameter) are gradually separated from coarser gravel
and much of the finer silt and clay. the sand then accu-
mulates along creeks and rivers in the intermountain
basins. For example, most sand in the Killpecker Dunes
originated from the appropriately named Big Sandy
and Little Sandy creeks that flow from the Wind River
Mountains. 1 these creeks were much larger when the
glaciers were melting, bringing large volumes of sand to
the area. Subsequently, westerly winds in the Holocene
blew much of this sand toward the east, across the Great
Divide Basin to the Ferris and Seminoe mountains.
Smaller silt and clay particles, known as loess, were
dispersed farther eastward onto the Great Plains. the
presence of different-aged sand grains in now-dormant
parts of the Killpecker Dunes suggests that sand move-
ment occurred in this area at various times over the past
20,000 years, probably most often during dry periods,
when the sand was more easily blown out of the creek
beds . 2
the kinds of plants growing on dunes depend on
the degree of sand stabilization as well as on tem-
perature, moisture, and the amount of organic matter
in the sand. only a few species can survive on shift-
ing dunes in Wyoming. they include blowout grass,
sand lovegrass, prairie sandreed, sandhill muhly, rusty
lupine, blowout penstemon, alkali wildrye, indian
ricegrass, and scurfpea . 3 t he coarser soils of dune tops
typically have different species than the finer-textured

Stretching across the intermountain basins of central
Wyoming are elongated mosaics of active and stabilized
dunes (fig. 9.1). Sand dunes create a dramatically differ-
ent environment in the semi-arid lowlands, primarily
because they provide a better water supply for plants,
due to the inverse texture effect (explained in chapter 3)
and because the shifting sand creates special problems
for plant establishment and growth. consequently, the
flora of the dunes is considerably different from that of
the surrounding shrublands. contributing to the bio-
logical diversity in some areas are small ponds that pro-
vide a source of water during the dry summer for plants
and animals that might not otherwise be able to survive
there.
Dune location depends on wind direction, a source
of sand, and barriers to sand movement. For example,
large deposits of sand are found on the westerly, wind-
ward foothills of the Ferris Mountains north of Rawlins,
the Laramie Mountains near Laramie, the Medicine Bow
Mountains in north Park, colorado (east of Walden),
and the Sangre de cristo Mountains (Great Sand Dunes
national Park) farther south in colorado. elongated
dunes are found in wind corridors where sand has been
funneled by the topography, such as the Killpecker
Dunes northeast of Rock Springs, and the dune fields
west and east of casper.
the origin of such large volumes of sand is one of
the first questions asked. the answer lies in the physical
weathering of various kinds of rocks over long periods

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