Below this region flow the streams of the Great Basin, none of which reach the sea, but either terminate in lakes having no outlet or else vanish in sloughs or " sinks."
In length and only a few inches deep. Such bodies often become nothing but vast sheets of liquid mud, and are called " mud lakes," a term most frequently applied to the sloughs fed by Quinn's river.
Eared grebes and ring-billed gulls breed on the sloughs of the plains, and rarely the white pelican nests about the lake shores.
Here and there faint depressions occur, occupied by marshy sloughs, or floored with a rich black soil of pestglacial origin.
Nearer the Great Lakes the till sheets are trenched only by the narrow valleys of the large streams; marshy sloughs still occupy the faint depressions in the till plains, and the associated moraines have abundant small lakes in their undrained hollows: hence these drift sheets are of late Pleistocene origin.