[Cletus.D.Yokel]

That giant caldera under Yellowstone park?
It used to be under the great lakes.
Michigan is the center plug.

Speculation

[Steve Van Doorn]

Yellowstone Caldera is moving east. I believe it started under Wallowa-Whitman National forest moved south to the Craters of the moon national preserve then up to where it is now. Generally going around the mountains.

12,600 years ago likely the Saginaw Michigan Impact Structure or massive solar flare/micro-Nova that caused the younger dryas. I don't know of any Caldera under that area.

[Pete from Shawnee Mission]

There was something else in Michigan and it was considerably bigger than the Yellowstone cauldera. There was a lot of lava but it did not move west. (Isn't geology fun!)

Midcontinent Rift System

"The Midcontinent Rift System (MRS) or Keweenawan Rift is a 2,000 km (1,200 mi) long geological rift in the center of the North American continent and south-central part of the North American plate. It formed when the continent's core, the North American craton, began to split apart during the Mesoproterozoic era of the Precambrian, about 1.1 billion years ago. The rift failed, leaving behind thick layers of igneous rock that are exposed in its northern reaches, but buried beneath later sedimentary formations along most of its western and eastern arms. Those arms meet at Lake Superior, which is contained within the rift valley. The lake's north shore in Ontario and Minnesota defines the northern arc of the rift. From the lake, the rift's eastern arm trends south to central lower Michigan, and possibly into Indiana, Ohio, Kentucky, Tennessee, and Alabama.[1] The western arm runs from Lake Superior southwest through portions of Wisconsin, Minnesota, Iowa, and Nebraska to northeastern Kansas,[2] and possibly into Oklahoma.[3]" ....Snip......

Had the rifting process continued, the eventual result would have been sundering of the North American craton and creation of a sea. The Midcontinent Rift appears to have progressed almost to the point where the ocean intruded.[7] But after about 15–22 million years the rift failed.[6][8] The Midcontinent Rift is the deepest closed or healed rift yet discovered; no known deeper rift ever failed to become an ocean.[7]