The Black Hills, Bear Lodge Mountains, and Devils Tower - Mountains and Plains: The Ecology of Wyoming Landscapes - page 268

Fig. 16.2. Devils tower, flanked by ponderosa pine savanna
and mixed-grass prairie. the grassland can be highly flam-
mable. common grasses include blue grama, western wheat-
grass, needle-and-thread grass, and little bluestem. Fisher et al.
(1987) estimated that the historic fire-return interval in this
area was about 14 years. Devils tower is one of a dozen igneous

intrusions in the Black Hills and Bear Lodge Mountains. the
others include inyan Kara Mountain, Little Missouri Buttes,
and Warren Peaks in Wyoming, and Bear Butte, Black Butte,
crow Peak, custer Peak, and terry Peak in South Dakota. eleva-
tion at the top of Devils tower is 5,117 feet. Photo by Hollis
Marriott.

More puzzling is the presence of plants that typi-
cally are found in the deciduous forests of eastern
north America, such as American elm, bloodroot, box-
elder, bur oak, hackberry, and hophornbeam, or species
from the boreal forests that stretch across canada, such
as bunchberry dogwood, canada scurvyberry, paper
birch, and white spruce. At least some of the eastern
species could have migrated westward along the moist
tributaries of the cheyenne River, where they still occur
in favorable habitat s. 7 t he northern species may have
migrated southward during the cooler periods associ-
ated with the advance of continental glaciers. the Black
Hills were not glaciated, but the boreal plants persisted
a short distance south of the ice front where the climate
was favorable.
the Black Hills and Bear Lodge Mountains are refu-
gia for many forest plants and animals that are sepa-
rated from their main populations by long distances
across grasslands. conservation biologists place great
value on such places, because they help maintain
genetic diversity. Without the habitat provided by

the somewhat cooler, wetter, largely forested environ-
ment of the Hills, the biodiversity of the region as a
whole would be lower. notably, the enabling legisla-
tion passed by congress for establishing Wind cave
national Park was to protect bison, elk, and pronghorn
as well as the cave itself . 8

Geomorphic Regions

the uplift and subsequent erosion of the Black Hills
and Bear Lodge Mountains have led to the formation
of five roughly concentric geomorphic regions that
strongly influence landscape patterns (see fig. 16.1) . 9
on the perimeter is the Hogback Rim, composed of
Mowry shale, Lakota sandstone, Fall River sandstone,
Minnewasta limestone, and other erosion-resistant sed-
imentary strata that were tilted upward as the moun-
tains developed. the rim is sharply defined to the east
and south but is more like a plateau on the west. Pon-
derosa pine savannas predominate on rocky soils, with
grasslands on fine-textured soils.