Green Circle on Rosevelt? Curiosity?

Question

I have used the google map and I have see the zone of the Roosevelt at the Coordinates below,I have notied in this zone some green circle.I know that this circles are for Agriculture,but I have Asked to myself what is the history of this form of Agriculture.I'm not a farmer,but only a curiosity-man.You know some site that talk about this?

Here the coordinates:

zone circles 1

lat 45°45'48.29"N

long 119°57'17.45"O

zone circles 2

lat 46° 0'47.24"N

long 119°35'3.96"O

zone circles 3

lat 45°45'50.97"N

long 119°34'51.56"O

zone circles 4

lat 46° 9'23.79"N

long 118°53'31.31"O

zone circles 5

lat 46°21'16.30"N

long 119° 8'59.81"O

zone circles 6

lat 46°41'12.46"N

long 118°55'25.94"O

zone circles 7

lat 47° 7'33.15"N

long 119°46'33.36"O

zone circles 8

lat 46°40'46.10"N

long 119°50'50.67"O

zone circles 9

lat 47°10'35.18"N

long 119° 9'45.76"O

Thanks at all!

Answer 1

The green circles that you are seeing are from center pivot irrigation systems.  The water source or pipe is in the middle of the field.  The irrigation pipe runs to the edge of the field and travels on a pivot anchored by the water pipe in the center of the field, so you end up with an irrigated circle of land.  While the entire field might be planted with the crop, there is usually not enough natural rainfall  to keep the corners of the field that don't receive water from the system green.  The result you are seeing is a green circle of a crop growing.