Were water to fill the basin today the hydrostatic pressure against the Slate Range would be over 600 feet, and when the bottom mud was being deposited, it would have been over 900 feet. This pressure was enough to cause a slow flow through the Slate Range mountains into Panamint Valley. At least some of this water permeated downward through the muds covering the bottom of the lake. At around 300 feet below the present surface this water encountered very permeable, soluble mineral beds through which it traveled laterally toward the Slate Range. When this happened the saline minerals were subjected to leaching which gradually altered them.
Sodium chloride is also very soluble.
This would be followed in order by sodium sulfate, the sodium carbonate fraction of trona, and Borax. The final mineral to dissolve would be the sodium bicarbonate left when sodium carbonate was leached from the Trona. The effect of this leaching is that the minerals in the saline beds 250 to 350 feet below the surface are present today in the opposite order in which they are found in the Upper Salt. The Thenardite and Halite are usually only present beneath about 350 feet, the exit level for the leaching waters. And this order is backwards from the order in which they had to have been deposited.