Old area excluding one state (6)
I believe the answer is:
oregon
'one state' is the definition.
(I know that Oregon is American state)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for oregon that I've seen before include "area of America" , "Salem is this State's capital" , "America's Beaver State" , "US region" , "area of the US" .)