Using
www.historicaerials.com it looks like the most recent time a barge was parked there was in 1988.
I recall talking to a SOO Line crew in the mid-1980s about International Salt (later owned by AKZO) which was just downstream from Morton Salt, on Goose Island. International received shipments almost exclusively by barge but the channel silted up so much that they were forced to go back to rail. International even when it was served by barge ordered a shipment of salt by rail once a year to keep the track active as a precaution according to the train crew I spoke to as they were switching International.
So Morton might have gone to all rail due to a similar issue with siltation preventing barges and their pushers from going that far upstream.
Dredging it might have stirred up toxic sediments also from earlier years when tanneries and factories lined the North Branch up to Irving Park Road.
Speaking of salt companies it appears that Detroit Salt on the South Side is no longer rail served and/or is no longer in operation from the most recent Google view. They were located at 3811 S. Iron Street and they used to receive hoppers of salt off the NS line that services industries in the Stockyards industrial park. Does anyone have any more information about this Detroit Salt operation?