Rochester was known as the Flour City until 1850. Wheat from the Genesee valley made its way to the city to be turned into baking ingredients needed by rapidly growing eastern citys like New York. The Erie canal made inexpensive transportation possible.
Soon the demand for more wheat shifted the productive fields westward, to Ohio, Illinois and other midwest areas. The wheat could travel through the Great Lakes in large ships, but once at the easten end of Lake Erie it hit the barrier of Niagra Falls and the relatively small width and depth of the Erie Canal. This, along with the development of railroads, meant that Buffalo had the opprotunity to become the new Flour City. Here, not only was the wheat milled, but it was also stored in the silos to insure product through the long winter.
So here we see a grain elevator and mill on the Buffalo waterfront. But it does not look too productive. What changed in 1930's was the opening of the Welland Canal and St. Lawrence Seaway, which allowed the large grain carrying ships to bypass Niagara.
Still some elevators and mills do operate in Buffalo,, most notably General Mills and Gold Medal Flour. But this is only a shadow of the golden days during the 1920's when dozens of elevators and mills operated and employed thousands.