This made me think of early civilizations that always sprouted on river valleys. Indus Valley, Nile valley, Danube, Yangtze ..when nomads became pastoralists and then agriculturalists, they must have relied upon water that came down from glaciers or flowed across other lands. River bed silt always has the best soil minerals for growing.

The river bed is full of minerals that it had carried with it..perhaps flowing over different rocks, it brings some with it? Contrast that today..where we have a 45 billion dollar Ag industry in California ..legit Desert.