Sifto Canada: produces road-salt, has enough stored and last year laid off a fifth of its workforce because its salt is transported by boat, and a harsh winter meant shipping was difficult. Sifto's cellars were filled, mining had to cease for the season.
Sifto is in Goderich, Ontario and provides road salt mostly for the Great Lakes region. It is a Kansas-owned subsidiary of Compass Minerals International, with salt mines in Cote Blanche, Louisiana and Cheshire, England. Of course. Nantwich was the salt producer for Victorian England, and Cote Blanche sits in Holocene coastal marshes full of salt domes. A salt dome, thank-you wikipedia, is formed 'when a thick bed of evaporite minerals intrudes vertically into surrounding rock strata'. Evaporite: crystallisation by evaporation, in this case, salt. Oh, it is interesting, the layer of salt is put under pressure where it begins to flow, being 'more buoyant than the sediment above it'. Eventually it breaks through the layers of sedimentary rock above it and forms excrescences — salt diapirs — at the surface where it can become a salt glacier. Gosh.
Salt domes, being impermeable, can trap oil above them — the source of most of the oil reserves along the Gulf of Mexico.
Nantwich salt was used by the Romans; 'wich' means a brine spring and Nantwich's pre-Roman Celtic name indicated a sacred grove. Do we want to know how old Nantwich's salt reserves are? yes. They are Triassic, 220 million years ago, formed from salt marshes.
Goderich's salt is Silurian (443 million years ago, since you ask), discovered in 1866 by a petroleum exploration crew, 300 m below the surface. Today, the mine extends over seven square kilometres 500m below Lake Huron.