Around 25 years ago my wife and I rode a noteably hilly ride here in the St Louis area along with a fellow who did it on a fixie so it's obviously been done.

The terrain in Iowa is obviously quite different from the mountains of Colorado but don't expect it to be like eastern Colorado either. You can have miles of relatively flat or maybe rolling hills and then encounter a river valley with hills that, while they won't be nearly as long, will be just as steep as the mountains.