The MacDonald Creek occurrence is based on a significant area of dolostone, which may be of interest because of its proximity to the Alaska Highway. The showing is centred on an arbitrary point on the north-facing slopes of Mount St. George, immediately east of MacDonald Creek, 2 kilometres southwest of Summit Lake on the Alaska Highway.

The dolostone belongs to the Lower to Middle Devonian Stone Formation (Geological Survey of Canada Map 1343A). Regionally, this unit is composed of various lithologies including sandy dolostone, and bedded dolostone and limestone (Geological Survey of Canada Memoir 373). In the Summit Lake area it consists of a facies of dolomitic evaporite and dolomitic breccia. These rocks are mostly pale grey and very finely crystalline to aphanitic, with few clastic impurites. Bedding is indistinct, although the evaporitic facies is commonly laminated. Interbeds of very dark grey, medium- to coarse-grained limestone may occur rarely. In this area, the formation is approximately 360 metres thick. Bounding stratigraphic units, namely the Early Devonian Wokkpash Formation and the Middle Devonian Dunedin Formation, are also slightly dolomitic. Below the Wokkpash Formation, the Muncho-McConnell Formation comprises fine-grained dolostone, but it is thinner and outcrops in relatively narrow bands in this area.

Structurally, the Stone Formation in the Summit Lake area lies in the core of a very open syncline with a west-northwest trending axis (Geological Survey of Canada Map 28-1963). The area is at the 'nose' of the northwest-trending and plunging Tuchodi Anticline, and is also disrupted by thrusts. All rocks belong to Ancestral North America (Geological Survey of Canada Map 1713A).