The incident happened around 4 p.m. Saturday at Gray Whale Cove State Beach.
Sheriff's officials said the suspect sexually abused a woman on a stairwell leading to the beach.
Investigators released a photo of the suspect who is described as a white man in his 30s, about 5'7", slightly overweight, and has dark brown hair.
He was wearing a dark navy-blue spandex style shirt, baggy cotton jogger pants, and he wasn't wearing any shoes or socks.
He also was wearing a black backpack at the time of the assault.
Those with information on the incident are urged to contact Det. Piper at 650-599-1536 or by email at JPiper@smcgov.org