City officials said the year-old statue at Ronald Reagan Sports Park likely burned last Thursday night, since the damage was discovered the next day.
Perry Peters, who helps run the non-profit that raised the $100,000 needed to erect the statue and develop the park, told the station he's angry.
"I felt that the people, the volunteers who built the park here without government funds, were insulted by this," he said.
In 1983, during his first term as president, Reagan reportedly praised Temecula in a speech before the U.S. Olympic Committee for raising the money to develop the park without help from taxpayers. That speech was inscribed on a plaque behind the statue.
CBS Los Angeles reports that no suspects have been identified in the torching and the park doesn't have security cameras.