The three were electrocuted Friday, one after the other as the wife and son attempted rescues, each coming in contact with a 12,000-volt power line that had fallen over in their backyard, authorities said.
San Bernardino firefighters arrived to find the three bodies, but it was too dangerous to free them, fire spokesman Jason Serrano said. A utility company finally cut the power.
The firefighters had been called to the scene at 5:45 a.m. by a 17-year-old girl who said her parents and brother had been electrocuted and were lying in the backyard, Serrano said.
"It's absolutely a tragic story," Serrano said.
The victims were identified as Steven Vego, 43; his wife, Sharon, 42, and their son, 21-year-old Jonathan Cole, according to the San Bernardino County Sheriff's Department.
Serrano said it was unclear why the line fell. However, strong winds were sweeping through parts of the region.
Southern California Edison president Ronald Litzinger said the investigation was ongoing.
"We will leave no stone unturned so that we can take appropriate corrective actions," Litzinger said.
Litzinger expressed his condolences and said the utility's employees were collecting donations for the family, which the company would match.
Frank Vego, the oldest victim's 48-year-old brother, said it was the second time power lines had fallen and set fires at the house.
"It does appear to me that something wasn't quite right," he said. "This is 2011, and families aren't supposed to be killed early in the morning by falling power lines."
Vincent Haydel, a Southern California Edison spokesman, said a relative told him that a power line went down in the neighborhood several years ago but he had no details and the company would have to investigate.
Authorities said Steven Vego went outside when he heard the noise and was trying to douse the backyard fire when he touched the power line, which he may not have noticed.
"The mother went out to assist him and she, too, became a victim," Serrano added.
The mother's body was found on top of her 21-year-old son who also had been electrocuted, said San Bernardino Fire Captain Michael Bilheimer.
The teenage girl and another brother, 10, were inside the home and were not harmed, authorities said.
The unusual series of events shocked even veteran emergency responders.
"I've never seen an incident with multiple electrocutions or injuries that were caused by this level of power," Bilheimer said.
Neighbor Stella White, 79, said she woke up to a loud "kaboom" and saw fire reflecting off her bedroom window. She stepped outside and saw firefighters, police and "God knows who else" swarming the tree-lined street, which lies below San Bernardino Mountain foothills.
Family friends and neighbors said Steven Vego was a plumber, his wife was a nurse at a convalescent home and her son wanted to be a paramedic.