Horseshoe Line

I don't much about the event, but it looks like 2 moderate to slow moving MCSs developed one in NW MN, and the other N IA. The downdrafts associated with both systems created fairly strong mesohighs, which continued to progress the squall lines on the leading edge of the mesohighs. So they both sort of formed one squall line, but were essentially two to begin with. Once again I know nothing of the events, and I am only trying to guess based on the radar image.
Horshoe Line

I am pretty sure that William is right. If you look, there are two seperate large regions of stratiform precipitation, one behind each line of convective cells. Looks like two large mature MCS's.