When the Rocky Mountains first crumpled skyward, 70 million years ago, the adjacent plains rose with them, producing a gradual rise from the High Plains to the eastern flank of the central uplift. Streams meandered eastward from the modest summits which were gradually eroded to the level of the sloping plain. A second uplift of what is now the Colorado Plateau and Rocky Mountain corridor began about 25 million years ago, significantly augmenting the elevation of the mountains and increasing the erosive power of the streams that flowed from the high country.
These streams and subsequent Pleistocene glaciers sculpted the mountains and foothills, removing overlying sediments and cutting numerous canyons through the ancient, Precambrian core. Rumbling onto the plains, the streams merged to form two primary channels, the South Platte and the Arkansas Rivers, their watersheds split by the Palmer Divide; this high, broad ridge, which rises between Denver and Colorado Springs, still connects the High Plains with the east edge of the Front Range. The Rivers and their numerous tributaries have molded a scenic terrain of valleys, low ridges, mesas and hidden canyons along the base of the Rockies, extending eastward along the channels of the primary streams; lower than the adjacent mountains and High Plains, this landscape is known as the Colorado Piedmont.
The great majority of Coloradans live on the Piedmont and its valleys of Cretaceous Pierre Shale support a large portion of the State's agricultural production. The numerous lakes and reservoirs of the Piedmont attract bald eagles and migrant waterfowl while the wooded streams and canyons host the greatest concentrations of eastern Colorado wildlife. Basking in the rain shadow of the Rockies, the human and wild residents of Colorado's Piedmont enjoy a spectacular climate while dodging most of the severe thunderstorms and blizzards that plague the High Plains.
