Des Moines is tough to describe. It’s overall flattish but in reality it’s long undulating slight down and up, like you might go from 800 feet to 900 feet over a mile of distance and back again. Des Moines Is at about 850-900 feet average elevation if I recall, and there is Sherman Hill, which is the highest near downtown. It might be 150 feet higher than the surrounding area.
western Iowa is in the lower extent and easternmost extent of the true Great Plains and is as much as 1600 feet in the northwest corner, and is 1/4 drier than southeastern Iowa, which is maybe 500 feet and greener/wetter and is not considered Great Plains so much