Mystery

I took a flight from San Francisco CA to Amsterdam (The Nederland, Europe). About two hours after takeoff, I made these photos. (I’m not an American and it was my first flight on this route, so I don’t know where I was on that moment). What can it be? Any idea?

Answer: The green circles are typical of irrigated land or fields where the irrigation equipment pivots around a well pipe. The spray equipment slowly revolves, but only sprays water under the area reached by the spray heads. Since it is anchored on one end, it can only revolve in a circle. This pattern is very typical of midwestern areas of USA not possessing natural abundance of water from rainfall, but having underground sources that can be used for irrigation.