Margaret Lake is located 6 kilometres northwest of 70 Mile House.
The lake is a semi-evaporitic playa lake. It is located in the "Green Timber Plateau" area (EMPR Bulletin 4), a semi-arid plateau area averaging 1130 metres elevation which is part of the Cariboo Plateau and host to several playa lakes. The area is underlain by alkaline plateau basalt flows of the Miocene to Pleistocene Chilcotin Group, mantled by a thin cover of glacial till and glaciofluvial sediments. Annual precipitation averages between 300 and 400 millimetres (EMPR Paper 1991-1).
Margaret Lake contains sodium carbonate-rich brine and "winter crystal" (natron or hydrated sodium carbonate). At the end of the dry season in 1937 (EMPR Bulletin 4) the eastern part of the lake was covered with a 1 centimetre-thick layer of natron. The lake is composed of brine to a thickness of approximately 30 centimetres, over an area of approximately 1.8 hectares. The "winter crystal" had a composition of 98.3 per cent sodium carbonate and 1.7 per cent insoluble material (EMPR Bulletin #4, page 17).