Petaluma police are seeking clues to the identity of a knife-wielding man who attacked a stranger with a large blade on a west-side street corner late Thursday night.

The 20-year-old victim suffered only superficial wounds despite the surprise 11:50 p.m. slashing at Western and Upham avenues, police said.

But it was unclear what prompted the behavior of the perpetrator, who wore a sheath containing the large bowie-style, fixed-blade knife with which he attacked his victim, authorities said.

The victim had just left a friend's house and was walking on Western Avenue when the hoodie-wearing stranger suddenly attacked him, pulling the knife from its sheath, police said.

The suspect then ran, allowing the victim to call a friend who picked him up and took him to Petaluma Valley Hospital for treatment.

Medical personnel alerted police to the incident, but officers were unable to find the stabbing suspect.

He was described as a white man aged 18 to 20, wearing a black, zip-up hoodie.

Anyone who witnessed or knows anything about the suspect is asked to call Petaluma Police Officer Eric Vera at 778-4372.