<P> The Black Hills also have a' skirt' of gravel covering them in areas, which are called pediments . Formed as the waterways cut down into the uplifting hills, they represent the former locations of today's rivers . These beds are generally around 10,000 years old or younger, judging by the artifacts and fossils found . A few places, mainly in the high elevations, are older, as old as 20 million years, according to camel and rodent fossils found . Some gravels have been found but for the most part, these older beds have been eroded away . </P> <P> As with the geology, the biology of the Black Hills is complex . Most of the Hills are a fire - climax ponderosa pine forest, with Black Hills spruce (Picea glauca var . densata) occurring in cool moist valleys of the Northern Hills . Oddly, this endemic variety of spruce does not occur in the moist Bear Lodge Mountains, which make up most of the Wyoming portion of the Black Hills . Large open parks (mountain meadows) with lush grassland rather than forest are scattered through the Hills (especially the western portion), and the southern edge of the Hills, due to the rainshadow of the higher elevations, are covered by a dry pine savannah, with stands of mountain mahogany and Rocky Mountain juniper . </P> <P> Wildlife is both diverse and plentiful . Black Hills creeks are known for their trout, while the forests and grasslands offer good habitat for American bison, white - tailed and mule deer, pronghorn, bighorn sheep, mountain lions, and a variety of smaller animals, like prairie dogs, American martens, American red squirrels, Northern flying squirrels, yellow - bellied marmots, and fox squirrels . Biologically, the Black Hills is a meeting and mixing place, with species common to regions to the east, west, north, and south . The Hills do, however, support some endemic taxa, the most famous of which is probably white - winged junco (Junco hyemalis aikeni). Some other endemics are Cooper's Rocky Mountain snail, Black Hills subspecies of red - bellied snake, and a Black Hills subspecies of southern red - backed vole . Some birds that are only in the Black Hills and not the rest of South Dakota are pinyon jay, gray jay, three - toed woodpecker, black - backed woodpecker, American dipper, ruffed grouse, and others . </P> <P> The northern Black Hills approximate Lawrence and Meade Counties and are roughly equivalent to the Northern Hills District of the Black Hills National Forest . The central Black Hills (the Mystic District of the Black Hills National Forest) are located in Pennington County west of Rapid City . The southern Black Hills are in Custer County and are administered in the national forest's Hell Canyon District . Finally, Wyoming's Black Hills follow the Bearlodge District, approximately Weston and Crook Counties . </P>

What kind of animals are in the black hills
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