The Rharian Field (Ράριον [sic!] πεδίον) was located in Eleusis in Greece and was supposedly where the first plot of grain was grown after Demeter (through Triptolemus) taught humanity agriculture. It was associated with the Eleusinian Mysteries.
Demeter was surnamed Rharias after the field, or after its mythical eponym Rarus.
References
Rharian Field Wikipedia(Text) CC BY-SA