Which is why you in the mountains mostly find gravel as that is what wind, rain (and the lovely acid in the rain) can do in mountains.
But seriously, erosion is from water. Large quantities of it, over many a years. Which is why sand is common at shores and in areas that was once the sea bed (Jutland is an excellent example of once sea bed). Should mountains that once were sea bed, but now are well obviously mountains, have contained sand on the surface, that has been washed away with rain over the millennia.
FYI I know there are quite a lot of different sand, but honestly, what kind of sand do you think this is. Any kind of special sand?.. No, it is the broad term of the word sand. Unless I'm mistaken, most people would probably think of beach sand than they would think of special type of red sand, no? In which case.. And I'm only saying this because it is fun.. Where do you usually find beach sand.. Around lakes and near oceans (not that we have oceans in-game yet). So most likely sand will be in areas with lots of water. It also includes rivers that are not subjugated to waterfalls, ie. quiet rivers such as in plains or close to the lake. Why not mountain rivers? The stream would carry the sand down to the point where the momentum is no greater than the resistance. That is usually at the end of the river, unless I've mistaken the whole point of gravity.
Just saying..
Oh yes, as a last note.. Calling other people uneducated, then to, again, quote a wikipedia article does -not- seem very educated.