Gypsum of Triassic age occurs at a single locality straddling the Alberta boundary at the headwaters of Forgetmenot and Fetherstonhaugh creeks. The occurrence was first described in detail in 1961.

Gypsum intercalated with dolomite and minor limestone is present in several beds of the Upper Triassic Starlight Evaporite member of the Whitehorse Formation. This unit is assigned a Karnian age and is correlated with the Charlie Lake Formation which is host to extensive anhydrite deposits further to the north. The presence of anhydrite is known from oil and gas drilling. The Starlight member, the lowermost unit of the Whitehorse Formation, consists of a recessive buff to light grey weathering sequence of interbedded dolomites, limestones, siltstones and intraformational or solution breccias. In the Forgetmenot Creek area, pale grey and yellowish brown to orange dolomite is intercalated with several gypsum beds. Also present are lenses of dolomitic and calcareous siltstone and pale grey limestone.

Gypsum is present in a minimum of 4 beds ranging in thickness from 2 metres to greater than 26 metres. Locally, it contains solution breccia and lenses of dolomite. The gypsum is typically white to cream to pale pink in colour. It is laminated to thin bedded and locally massive. Trace amounts of pyrite are present.

The beds strike northwest with dips of 25 to 30 degrees southwest. In outcrop, the gypsum can be traced along strike for 500 metres. The presence of sinkholes suggests that the gypsum may extend further south. Gypsum occurs over a minimum stratigraphic thickness of 100 metres and contacts between gypsum and overlying or underlying rocks are invariably marked by sinkholes up to several metres in diameter.

Drilling indicated that the gypsum grade is more variable at depth than in surface exposures. Gypsum content in the subsurface varied between 75 and 80 per cent while surface sampling indicated a purity greater than 90 per cent gypsum (Open File 1991-15). Sampling by Butrenchuk confirmed the high purity, varying from 84 to 98 per cent (Open File 1991-15).

Reserves on the property are estimated to be 2.3 million tonnes with a potential for 25 to 30 million tonnes if the gypsum persists along strike (Open File 1991-15).