North Dakota is flat.
Okay, so parts of North Dakota are very flat. The Red River Valley is, in fact, the flattest bit of land on earth, but that's only a small part of the state. The rolling hills of the prairies in the eastern and middle part of the state, and the Badlands in the west are anything but flat.
There was a humorous article published in an otherwise prestigious peer-reviewed journal in which the researchers did an electronic topography of a pancake and an elaborate statistical summary of the topography of Kansas and concluded that yes, Kansas is actually close to 100 times flatter than a pancake. I'm guessing it was one of those "We have the equipment so we did the experiment, and since we did the experiment, why not write it up and see if they'll take it?" and then it actually got published
ETA: found it! http://www.improbable.com/airchives/paperair/volume9/v9i3/kansas.html Includes lines like "Some readers may find the comparing of a pancake and Kansas to be analogous to the comparing of apples and oranges; we refer those readers to a 1995 publication by NASA’s Scott Sandford (3), who used spectrographic techniques to do a comparison of apples and oranges." Also, their conclusion: "After many hours of programming work, we were able to estimate that Kansas’s flatness is approximately 0.9997. That degree of flatness might be described, mathematically, as “[dingdangity] flat.” "
Interesting! It is worth noting that the "valley" formed by the Red River of the North, is not actually much of a valley and, at Fargo, is only a few hundred feet wide. It merges almost seamlessly into the ancient Lake Agassiz lake bed. This is one of several reasons why the flooding in Fargo and Grand Forks is so bad (the other two major reasons being that it's a meandering river, with hairpin curves and near loop-de-loops, and also that it's north flowing). As you travel west from Fargo, the ancient lake bed gives way to the beautiful rolling hills of the prairie, then into the Badlands. It's gorgeous country, btw. If you've never been, I highly recommend visiting. Well, during the spring and summer, anyway! It can get a bit brutal during the winter (though still gorgeous.)
NDSU has a great website describing the geology of the area, if you're interested. http://www.ndsu.edu/fargo_geology/briefhistory.htm