Jerusalem artichokes were probably native to the central part of our continent. They likely spread eastward in pre-Columbian times as a native food and item of commerce. Since European arrival, they have spread to most of the rest of the country. The species is quite variable in size and leaf shape, and adds more than its share to the difficulties in identification with sunflowers. Digging up the roots would help alot, but please don't unless you're going to eat them.
I noticed when I added the image on the wildflower page to the album that all my sunflower images are shots of partial flower heads, and all look a lot alike. In my effort to find interesting images, I ended up with boring!