The great Plains cover about 2.6 million square kilometres. On the flat eastern side the grass grows more than 3 meters high while on the western side it is short and spiky. Here the ground is spread with rocky outcrops, known as buttes, and stony slopes called badlands. The temperature reaches 38ºC in summer with whirlwinds and thunderstorms, and –5ºC in winter when the land is covered with snow. More than thirty nations, 150,000 people, lived on the Great Plains in 1800. Dakota, called Eastern Sioux by the white settlers, were the most powerful nation; they lived as nomads, hunters and traders moving from places to places following the big herds of buffalo across the Plains. The Dakota men were great warriors who attacked regularly the smaller and weaker nations such as the Pawnee and Comanche to steal their weapons and horses. In the nineteenth century they fought bravely against the US Army who protected the settlers, mainly farmers and ranchers.