Moments before 6 a.m., the man handed a Denny's cashier a note demanding cash after finishing his meal. Noticing the butt of a handgun in the man's waistband, the cashier gave him the money, police said.
Sgt. Lisa Hugdahl said there were a few other patrons dining in the restaurant during the robbery, but that they did not appear to notice the crime in progress.
"It was pretty low-key," she said.
The suspect -- described as a thin, bald Hispanic man in his mid 20s clad in black - was last seen on foot toward Contra Costa Boulevard.
Anyone with information about the robbery is urged to call the Pleasant Hill Police Department's investigations division at (925) 288-4630.