Allen will join senior cornerback T.J. Bryant and junior safety Jawanza Starling as Trojans who starred at Lincoln in high school.
Selecting USC over Alabama and Auburn, the 6-foot-1, 210-pound Allen offers a change of pace from the smaller, quicker rushers that have populated coach Lane Kiffin's initial recruiting classes.
With Marc Tyler, the only big tailback on the Trojan roster, entering his senior season, Allen could compliment a Dillon Baxter or D.J. Morgan starting in 2012 as part of a "Thunder and Lightning" duo.
Rushing for more than 700 yards and nine touchdowns as Lincoln won the Class 4A state title last season, Allen has also drawn praise for his abilities in the passing game with 17 receptions as a senior.