Re: Where does Alkaline come from?--Alkali desert?

Hello, Andrew...

The quick answer is that the alkali are from the decomposition of rocks, and/or volcanic activity.  
Decomposition of carbonate rocks releases carbonates, many of which have chemically alkaline 
characteristics, and some volcanic regions have extremely alkaline lakes (the most famous of which are 
probably those in the rift valleys of East Africa, which are loaded with sodium carbonate).

Usually such alkali are carried to the sea and dispersed into the ocean, but in the case of lakes with no 
outlets (as in Mono Lake, Great Salt Lake, the now-dried-up Lake Bonneville, etc) they will accumulate and 
if the lake then dries up (as in many areas of the western US), the alkali is precipitated out and remains in 
the soils, giving them an alkaline character.