(CNN) -- Two people were killed and one was seriously injured when a rare tornado struck a family ranch in northeastern Montana, the Sheridan County coroner said Tuesday.
The National Weather Service in Glasgow, Montana, confirmed that a tornado touched down 9 miles west of Reserve in Sheridan County about 7:15 p.m. Monday.
Steven D. Smith, 46, and Robert Richardson, 10, were found dead at the scene, the coroner's office confirmed in a statement Tuesday. Emergency crews found Smith 200 feet from the home; Richardson was discovered in the basement. Coroner Dave Fulkerson attributed their deaths to "blunt-force head and chest injuries."
"They died very quickly," he added.
Richardson's grandmother, Barbara Smith, 71, was also found in the basement of her demolished home with unknown injuries. She was taken to Sheridan Memorial Hospital in Plentywood, Montana, and was later moved to a hospital in Billings. She is listed in serious condition, hospital officials said.
"The people killed were very well-known," Fulkerson said. "It's going to have a devastating effect on the community."
Emergency responders sustained the only other storm-related injuries, the coroner's office said.
The storm started about 5:30 p.m. near Opheim, said Victor Proton, a senior forecaster at the National Weather Service in Glasgow.
It was "kind of an on-again, off-again tornado-producing storm," Proton said.
It died down almost three hours later in North Dakota, he added.
Although there were reports of large hail and heavy rains in neighboring areas, the Smith family ranch was "basically greeted by the tornado," Proton said. The only warnings they may have had aired on either local television reports or weather radio. The closest news station is in Billings, more than 300 miles away.
"Think of the 1950s. That's the kind of area you have," Proton said. "It's all farm land, no subdivisions ... just miles of fields."
He said tornadoes in the area -- along the Canadian border -- are extremely rare, although another was reported elsewhere in the state this year.
As of the 2000 census, Sheridan County had a population of 4,105.