At my small D1 school (6,000 undergrads) we kept social activities pretty much in the track and XC family (guys & girls).
Now, my perception is that most teams men's at my school were the same way, not terribly social with the other teams -- except for like the hockey & basketball teams. Pretty much all the teams had their own off-campus houses.
Girls teams were all over the place. But, of course, girls track spent most of their time with us.
Curious to hear others' experiences.