@rosborne979,
Get a glacial history map of Lake Michigan. The two glqciql lobes, The Green Bqy lobe and the Lqke Michigqn lobe are probably the source rocks for the erratics you see on the shore.
The bedrock geology of the Milwaukee area is mostly carbonates so its probable that those rocks have been eroded and piled on by a moraine of gneiss and grnites(bot of which are found in the Sudbury geo province from NW Wisconsin all the way NE.
You have enough to figure it out with a state geological (bbedrock and glcial mp)