"I committed about an hour ago. I was offered early today," Pinner said. "I talked to my coach and talk to my parents and just made my decision from there.
"I like the way the campus looks, how the coaches are real cool and I know the tradition at USC is real great."
Pinner was expecting an offer from the Trojans but was surprised by the timing.
"Coach was telling me that they were going to pull the trigger earlier, but I didn't think it was going to be this early," he said. "I thought they were talking about in a couple of weeks."
The 6-2, 225-pound back is known for his physical running style and has also served as a lead blocker at times for the Diablos.
He showcased his athleticism and pass catching ability at the recent Los Angeles Nike Camp, where he was named the Running Back MVP.
Pinner said he will get the opportunity to compete at both fullback and tailback at USC.
"I am really more of a bigger back but I am also quick and fast, which I have been working on for the past year," he said. "I am trying to get my speed and quickness up so I can be a better all-around back."
Pinner will be reunited with his former high school teammate, Tre Madden, who is a member of USC's 2011 recruiting class.
"It's always good to know that you are not going in there alone," Pinner said. "We have been playing on the same team since we were about ten."