A northern Santa Rosa apartment fire started around 7:30 Thursday morning causing $100,000 dollars in damage. A resident heard a loud boom, smelled smoke and discovered smoke and flames spreading along the floor of the apartment. He called 911. Santa Rosa firefighters responded and contained the flames to an upstairs bedroom in about 20 minutes. It is still under investigation. A dog was found unharmed under a couch about 35 minutes after the fire was reported. There were no injuries.