Big old bur oak - Upper Sioux Agency State Park
Near Granite Falls, Minnesota.
Back in the pre-settlement days (which this conceivably could date back to) bur oaks were usually surrounded by prairie grasses (see www.flickr.com/photos/22120384@N02/6212981389/in/pool-522... for one closer to that). The prairie fires would kill most of the woody plants, but the bur oaks were more fire resistant and usually survived. With the end of prairie fires, most are now surrounded by dense undergrowth.