Gondolas?

[pgandw]

Until at least WW1, western railroads tended to use gondolas instead of hoppers for hauling coal. Until more specialized cars became common, flat cars/gondolas were the universal cars for bulk commodities not needing protection from weather. Gondolas were quickly made by adding side and end boards to a flat car - the height of the boards depending on the anticipated weight of the load. You couldn't haul as much of a heavier commodity (ore instead of coal), so lower sides would be used.

Even after WW1, side and center dump gondolas were often preferred over hoppers in the West.

my thoughts, your choices
Fred W