Mono Lake is naturally salty and alkaline because it has no outlet. The only way water leaves is via evaporation. The Sierra streams that flow into Mono contain only trace amounts of minerals and salts but those minerals and salts stay and their concentrations, over the years, multiply. The City of Los Angeles, hundreds of miles to the south, has been diverting water from the Mono Basin since 1941. That diversion has cut the lake volume in half and has doubled its alkalinity and salinity.
Mono Lake is a geologist's paradise.
Two of the islands on the lake are volcanic domes. No area volcanoes are active at the moment but the area shows many signs of potential eruptions. Tufa are made from calcium carbonate which makes its way into the lake from underground springs. The calcium and carbonate combine to form limestone which builds up over time around the lake bottom spring openings. Declining lake levels have exposed the tufa towers we see today.