The attack happened at about 10:30 p.m. in Munson Park, on Manuel T. Freitas Parkway near Las Gallinas Avenue in Terra Linda, police spokeswoman Margo Rohrbacher said.
The male suspect approached the woman from behind with a knife, forced her to the ground and sexually assaulted her, Rohrbacher said.
The woman went home and called police, and was then taken to a hospital for treatment and a medical exam, Rohrbacher said.
Investigators searched the park today for evidence and canvassed the neighborhood for witnesses, Rohrbacher said.
The suspect is described as a white or Hispanic male about 6 feet tall and weighing 250 pounds. He has a goatee and thick lips, Rohrbacher said.
Anyone with information about the case is asked to call San Rafael police at (415) 485-3000.
