A 67-year-old man was beaten and robbed in the parking lot of the Graton Resort & Casino in Rohnert Park Tuesday morning, an attack that left him with severe head trauma, the Sonoma County Sheriff's Office said.

Deputies were called to the scene around 6:30 a.m. and found that he had been struck in the head with an unknown weapon and robbed of an unknown amount of cash and other property, according to a departmental release.

The man, whom deputies did not identify, told investigators from the Violent Crimes Unit that at least two people were involved in the assault.

He was transported to Santa Rosa Memorial Hospital.

Deputies and casino security are investigating the attack.