May 9, 2009: North of York, Nebraska, on my way back from Denver. I took US 34 through about the central third of Nebraska.
The 100-degrees-west line of longitude, which is still a ways west from here, is judged by one standard to be “where the plains begin” because that’s where rainfall patterns change. It even made it into a song. However, I would argue that US 81 — or even US 75 — is a little better indicator for travelers. Once you get west of it/those, the odds of easily finding a gas station, hotel, or food (particularly fast food) within half an hour start decreasing. (That’s especially true off the interstates.)