The boundary of the Quesnel Highland is not precisely defined in Holland, and in some interpretations it may be considered to be part of the Interior Plateau, as Holland defines it, or as a subrange of the Cariboo Mountains. Those mountains also, in some reckonings, are classified as part of the Interior Plateau rather than their usual association as the northernmost subrange of the Columbia Mountains. Generally it is composed of the lower, westerly valleys of Horsefly Lake, Quesnel Lake, and the Bowron Lakes, most of the Cariboo goldfield towns and similar terrain northwestwards, to about where the Willow River rounds the northern end of the Cariboo Mountains to join the Fraser River.