This term is used by people in Los Angeles, when referring to travelling within Orange County. This refers to the idea that people in Orange County know nothing about what's going on in Los Angeles or even the world, and only are concerned with local affairs.
Comes from the term for Russia "behind the iron curtain" from the cold war era.
Man, I had to go "behind the orange curtain" the other day to visit my cousins. They still think rockabilly is cool!
How come you missed the big concert? Oh man....since I moved behind the Orange curtain, there's no way for me to keep up with what's going on.....there's no LA Weekly or anything!