The Hadrynian Horsethief Creek Group that underlies much of the northern Selkirk Mountains is divided into three members. The upper pelitic member is overlain by latest Hadrynian to Lower Cambrian rocks of the Hamill Group and is correlated with the Yankee Belle Formation of the Cariboo Group in the Cariboo Mountains to the northwest. The underlying middle marble member is correlated with the Cunningham Formation, and the lowest exposed lower pelitic member with the Isaac Formation.Westward thickening of the Horsethief Creek Group is paralleled by a gradational change in the upper pelitic member from a predominantly clastic sequence to the east to a predominantly calcareous sequence to the west. The overlying Hamill Group also changes in character, becoming more pelitic and interdigitating with basaltic metavolcanics toward the west. These facies changes are compatible with results from adjacent areas that point to deposition on a continental shelf in late Proterozoic to early Paleozoic time.