According to Pro-Football-Reference, the USC Trojans are tied for the most active NFL players (with Miami) at 41. That number might not go up this year.
In Dane Brugler's CBS Sports mock draft, he has no Trojans in the first round. Rob Rang has Matt Barkley going to the Cardinals at pick no. 7, but there still seems little guarantee that the Trojans QB will go that high or in the 1st round at all. Rang also has USC wide receiver Robert Woods going to the Texans at pick no. 27, but he does not have Woods in the top 50 of his big board.
Last season, there were three Trojans drafted: OT Matt Kalil at pick no. 4, DE Nick Perry at pick no. 28, and FB Rhett Ellison at pick no. 128. Unless Barkley has a great combine and pro day, it seems increasingly likely that USC won't have anyone in the top 15 picks of this year's draft.
As history has shown us, that's quite unusual. But by looking at the prospects coming out of Southern California this year, it's not surprising.