In my home town, Independence, Iowa, there is an old grain mill on the Wapsipinicon River that has been preserved. It's one of the few remaining in the state, and one of the largest. It is full of wonderful old, mostly wood technology for processing various types of grain. http://www.buchanancountyhistory.com/mill.php
A grain-grinding wheel, about 4' in diameter.
There were also some great old logos, some of which I remembered.