Orange County Observer

Why Some Lakes are Salt,

The cause of the saltness of some American lakes is too patent to require many words of explanation. It is probable that, when the continents were raised from the sea, the lake-basins had been already formed, and came up, therefore, brimful of water. In the northern and eastern part of the continent, where the supply from rain and snowfall exceeds the loss by evaporation, the salt, being continuously carried away through their outlets, has become so diluted as to be an imperceptible quantity. In arid regions, as the Pacific slope and the country about the Caspian, where the evaporation was in excess of the supply, the water-level of the lakes continuously sank until, on account of the diminished extent of surface, the equilibrium of loss and gain was attained.
Hence the exceeding saltness of Great Salt Lake, the Dead Sea, etc.
For a like reason the water of the Mediterranean contains more salt relatively than that of the ocean.
Evaporation exceeding the supplies from the rivers and rainfall, it requires a constant current through the Strait of Gibraltar.
The same is true of the Red Sea, causing a like current through the Strait of Bab-el-Mandeb.
Other salt or brackish lakes probably owe their saltness to the supplies from the land.
Water being the most general of all solvents, the rains gather up the chloride of sodium from the soils and the disintegrating rocks, and where the streams fall into lakes whose only outlet is evaporation, the land itself must be a constant source of saline supply, and their waters must become more and more salt, until their capacity as a solvent has been reached.
The Utah Basin must once have been filled to its brim with ocean water. The outlet has been evaporation. The lake, receding to its present level, has left many evidences of its former extent.
[Popular Science Monthly.