I doubt they were grain stores, but elevators in the USA store grain and corn like that all the time in a pyramid shape and it doesn't hurt the grain / corn (other than moisture).

There is a "ski Indiana" photoshop showing a skier on one of these grain hills.

Here is a nice little pdf with a lot of ways we store product http://calculators.agstar.com/uploads/GrainStorageMethods070...

[edit: I agree they would have been a bad shape of an old style grain store, plus wrong era]