Congratulations to Rick Tegtmeier. This is Windmillgrass (Chloris verticillata).
When the seed head separates from the plant in the fall, it rolls like a tumbleweed and spreads its seed over the landscape. It has been present in central Iowa for only a few years. It is a warm season that is damaged by cold winters and was generally found in Missouri and south until recently. It is often seen along the curbs of streets and other compacted areas.
This is a relatively new arrival in central and northern Iowa. It is a perennial warm-season grass that forms an expanded panicle seed head late in the summer. It is generally found in dryer compacted areas. Any guesses?