Geology of the Carcross (105 D/2) and part of the Robinson (105 D/7) map areas, south of Whitehorse, Yukon, were mapped at 1::50 000 scale during the 1988 field season. The map areas are within the Teslin Plateau and Boundary Ranges physiographic regions.
Rocks of the Atlin (Cache Creek) Terrane, Whitehorse Trough and Coast Plutonic Complex are each represented in the study area. The Atlin Terrane is bounded by the Nahlin thrust fault and the Crag Lake tear fault. The Nahlin Fault is westerly verging and was active during Late Cretaceous time.
The westernmost exposures of Whitehorse Trough strata are those of the structurally complex Tally Ho Shear Zone, the northern extension of the Llewellyn Fault. This structure invovles rocks as young as Cretaceous.
Two ages of Cretaceous volcanic activity are represented by the Carmacks and Mount Nansen Groups. Rocks of the Montana Mountain volcanic complex are early Late Cretaceous in age (88-99 Ma).
Mineral occurrences of the Montana Mountain area are at least as young as Paleocene and are related to the Nahlin Fault. Other mineral occurrences in the area are spatially related to the Tally Ho Shear Zone.