Glacial lakes were formed in the Fort Nelson area by eastward-retreating Laurentide glacier ice that dammed a number of streams. These lakes drained through spillways at progressively lower elevations as the ice retreated eastward. A terrace on the Muskwa River containing sediments dated ca. 9000 years BP indicates that the river had entrenched itself between 50 and 70 m below the surrounding upland by that time. Prior to final entrenchment by the Muskwa River to its present grade, a pause in downcutting ca. 9000 years BP occurred, resulting in the formation of the terrace.