The Great Plains occupy the interior of the North American continent and are the homeland of the Plainfolk Mutes. They are the principle battlefield in the Amtrak Wars, with the Amtrak Federation's forces advancing from the south against the Mute clans in the north.
In specific usage, the Great Plains occupy an area approximately 500 miles across, from the Mississippi River to the Rocky Mountains, and roughly 2,000 miles long, from northern Mexico into Canada. The states of Colorado, Kansas, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas and Wyoming are located within this region.
In general usage, most notably with reference to the term 'Plainfolk', the plains are held to simply stretch from the Rockies to the Appalachian Mountains and from the Gulf of Mexico to the Great Lakes, comprising more or less the interior plains of all the former United States, as well as more temperate lands in the east, towards the borders of Ne-Issan.
The Great Plains are colder in the north and warmer in the south, with herds of buffalo and other wild animals roaming free across much of their extent. The grass and trees of the plains, as everywhere else in the world, has been turned red by an unforseen side-effect of the radiation released into the atmosphere by the War of a Thousand Suns.