What is the name of the broad expanse of flat land in the western United States and western Canada  where the species of plant called the Polygonum sawatchense of the buckwheat family be found?
Polygonum sawatchense Polygonum sawatchense is a North American species of plants in the buckwheat family. It in the western United States and western Canada, from the Pacific Coast to the western Great Plains, so from British Columbia south to California and east as far as New Mexico, Colorado, Saskatchewan, and the Dakotas.
Artemisia tridentata Artemisia tridentata, commonly called big sagebrush, Great Basin sagebrush or sagebrush, is an aromatic shrub from the family Asteraceae, which grows in arid and semi-arid conditions, throughout a range of cold desert, steppe, and mountain habitats in the Intermountain West of North America. The vernacular name "sagebrush" is also used for several related members of the genus "Artemisia", such as California Sagebrush ("Artemisia californica").