The plains extend from northwestern Canada through parts of Manitoba, Saskatchewan, and Alberta and into the United States, where they continue south to Texas. The landscape was largely formed as beds of sands, gravels, silts, and muds were deposited by streams flowing from the Rocky Mountains to the west. Over the top of these deposits is a layer of wind deposited silt, often called loess. Record highs have been recorded up to 118 degrees in the summer of 1936, to record low temperatures of minus 47 degrees in 1899. Annual rainfall averages only about 15 inches.
Fertile soil coupled with scant precipitation is the ideal combination for grassland.
Before the farmers began turning the sod, the area was a vast sea of tough, course blue-stem bunch grass and short green buffalo grass which sustained enormous herds of bison. These animals came to North America from Eurasia by crossing the Bering Strait land bridge in prehistoric times. Until the 19th century, as many as 60 million bison lived on the Great Plains from Mexico into Canada, and some were found east of the Mississippi River. The bison were central to the existence of the Plains peoples who used them for food, hides, and bone implements. Even the dried dung, called buffalo chips, was used as fuel.