Kenneth Robert Calkins, Jr., 45, was spotted driving recklessly near Payran and Madison streets at about 6 p.m., according to police.
Officers pulled over his car and found that Calkins appeared to be intoxicated, police said.
Calkins was arrested on suspicion of DUI. A search of his car revealed a shotgun with ammunition, which he is not allowed to own due to prior convictions, according to police.
Calkins was booked into Sonoma County Jail on charges of being a felon in possession of a firearm, driving under the influence and resisting arrest.
He was being held on $20,000 bail, police said.