The road winds on and on -- we stop for rests and lunch, exchange small talk, and settle down to the long ride. The beginning fatigue of afternoon balances the excitement of the first day and we move steadily, not fast, not slow.

We have picked up a southwest side wind, and the cycle cants into the gusts, seemingly by itself, to counter their effect. Lately there's been a sense of something peculiar about this road, apprehension about something, as if we were being watched or followed. But there is not a car anywhere ahead and in the mirror are only John and Sylvia way behind.

We are not in the Dakotas yet, but the broad fields show we are getting nearer. Some of them are blue with flax blossoms moving in long waves like the surface of the ocean. The sweep of the hills is greater than before and they now dominate everything else, except the sky, which seems wider. Farmhouses in the distance are so small we can hardly see them. The land is beginning to open up.

There is no one place or sharp line where the Central Plains end and the Great Plains begin. It's a gradual change like this that catches you unawares, as if you were sailing out from a choppy coastal harbor, noticed that the waves had taken on a deep swell, and turned back to see that you were out of sight of land. There are fewer trees here and suddenly I am aware they are no longer native. They have been brought here and planted around houses and between fields in rows to break up the wind. But where they haven't been planted there is no underbrush, no second-growth saplings…only grass, sometimes with wildflowers and weeds, but mostly grass. This is grassland now. We are on the prairie.