A Really Tall Tank

While researching the bridges that cross the Calumet River for the Pittsburgh, Fort Wayne, and Chicago Railroad, I noticed the CHICAGO MUNICIPAL AIRPORT 8 MILES "sign." And then I noticed the length of the shadow of the tank with that sign. Note that it is three or four times longer than the shadows of the bridges and the grain elevator in the lower-right corner. A satellite image confirms that this tower has been demolished. Note that the Skyway (I-90) now goes through there. I wonder what was stored in that tank.

ILHAP