Topographically the country traversed by the Porcupine river between the International boundary and the Yukon falls into two distinct provinces. The most easterly of these includes the low mountain and hill country extending westward from the boundary about 100 miles. The Yukon flats comprise the westerly belt.
A little more than 100 miles of the lower course of Porcupine river lie in the extensive alluvial plain known as the Yukon flats. Along this portion of the river hard rocks nowhere outcrop. The banks rise generally 12 to 18 feet above low water and never more than a few feet above high water. Entirely without topographic relief, this extensive region is covered with muskeag, spruce forest, and willows. The latter occupy the intermediate border between the swampy muskeag and the better drained spruce forest tracts, as well as the areas subject to river overflow. Numerous sloughs or side . . .