From the George Mason Student Handbook:
George Mason vs. James Madison Rivalry
The Patriots and Dukes, located just 95 miles apart, annually meet head to head to compete in 18 sports. Both schools are members of the 10-school Colonial Athletic Association.
With students from many local high schools attending the two universities, the matches offer opportunities for friendly competition between former classmates and often serve as natural high school reunions. As one of the best in-state rivalries, George Mason and James Madison basketball games are hard to match in spirit and intensity. After a James Madison loss, George Mason students can be heard chanting "66 West, 81 South" in reference to how the losers drive home.