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.
Eriogonum brachypodum Eriogonum brachypodum is a species of wild buckwheat known by the common name Parry's buckwheat. This annual herb is native to the southwestern United States from California to Utah, especially the Mojave Desert, where it grows in sandy and gravelly substrates. It has a skeletonlike spindly stem which branches many times, reaching anywhere from 5 to 50 centimeters in height and up to a meter in width. There is an array of rounded, dark-colored leaves around the base, each a few centimeters long and fuzzy on the undersides. Most of the plant is actually the spreading inflorescence. At intervals on the otherwise naked branches hang tiny clusters of glandular flowers a few millimeters wide in involucres of bell-shaped bracts. Each flower is less than three millimeters wide.