I'm wondering why they are built so tall and narrow. Does the packing of the contents under their own weight somehow prevent spoilage? I can't imagine storage space is at all that much of a premium on farms ...
The answer is to do with the way they have to be emptied under gravity. There is a cone at the bottom whose sides have an inclination angle (from the horizontal) greater than the angle of rest of the bulk grain. Hence a tall thin silo can be properly emptied whereas a short fat one could not (by gravity).
To make it easy to unload the silo for delivery. It also provides lots of volume on very little ground area. In California there are a lot of flathouses, just buildings at ground level. Grain has to be removed by power equipment.
