The assault happened around 7 p.m. Tuesday as the girl was walking home through a field near the intersection of Riverside Drive and Laguna Avenue.
Police say the suspect engaged the girl in conversation and when she turned to walk away, he knocked her down from behind and assaulted her.
The victim eventually was able to run away. The suspect then fled in an unknown direction.
Police released a composite sketch in hopes of identifying the suspect. He's described as white, about 6 feet tall, and in his late 20s. The man was wearing glasses and a bandana, and may have a tattoo on his upper right arm.
Anyone with information was urged to call the Riverside County Lake Elsinore Sheriff's Station at (951) 245-3300.