Why are those round things I saw from my airplane window?

Question

Flying east from SF to NY, I saw these huge circles on the ground. We could have been over Nevada, Idaho, Montana - I have no idea. Please don't answer "crop circles"!! These were something agricultural or industrial. What are they?

Answer 1

Just crops. An easy way to irrigate. If your sprinkler system is a pipe from the center and rotates from there, you end up with a crop field that looks like a circle.

It's called center pivot sprinkler irrigation.

Answer 2

Agricultural harvesting circles. No big deal.