I've never gotten close enough to this structure to find out exactly what it is. It is located on a "dead loop" of the Mouse River. The dead loops were created after the 1969 flood. In an effert to avoid another flood like the one in 1969 they straightend out portions of the winding river so flood waters would pass through the City without harm (a good plan but not good enough for the flood of 2011).
At first I assumed it was an old bridge footing but there is no similiar structure on the other bank so it may not be a good assumption. Do you have any ideas as to what it is?
I checked with Ron Merritt,Director of Minot Park District (whom I just had a radio interview with) and it may have been the Bear Castle pictured below. The face of the park changed greatly when they rechanneled the river as mentioned below. Also I miss reported... it is not on a dead loop but on the bank of the "newly" cut river.