Another way to remove salts is through desalinization plants. It is the removal of salts from a type of water called Saline Water. This method along with mining the salt is becoming a more and more popular way of providing freshwater to many needing countries world wide.
Where, do you ask that the salt layers came from? Well, there are two theories. One says it is caused by the evaporation of old seas. And the other says the salt layer was created by chemical reaction. So which is true? You be the decision maker of that.