Thanks, Bun. You're right about that. Thanks too for explanation about the Black Canyon.

Charley, your comment about coral reefs is a good one. I can find coral reefs off the Florida Keys, I bet.

Somebody asked me if there are irrigation pivots (which make the bold circles) in California. There aren't. It turns out that the pivots are used where groundwater is tapped for irrigation. In areas where streams bring water from mountains, the irrigation ditches are linear and fields are rectangular.