A Ventura woman whose skull was fractured this week by a rock thrown from a freeway overpass was recovering from brain surgery, authorities and family members said Friday.

Monica Dalto, 36, was heading home from Los Angeles International Airport about 9:30 p.m. Wednesday with her husband, Brian, when a softball-sized rock crashed through the sunroof of their car and struck her in the head, said Russ Whitmeyer, her uncle.

Dalto is a nine-year veteran of the Ventura County Probation Agency, said Chief Probation Deputy Alan Hammerand.

California Highway Patrol investigators determined someone threw the rock from the Wendy Drive overpass while Dalto's vehicle was northbound on Highway 101, the CHP said in a prepared statement released Friday.

Whitmeyer said the rock landed in the back seat, where the couple's 1-year-old daughter usually sits in a car seat. The child was not in the vehicle at the time.

When the rock hit Dalto, her husband was at the wheel. He was unable to call for help on his cell phone, so he drove as fast as he could to St. John's Regional Medical Center in Oxnard, Whitmeyer said.

On Thursday, surgeons picked bone fragments out of her brain and inserted a titanium plate in her head, Whitmeyer said. She remained in intensive care Friday but is expected to make a full recovery, he said.

"She seemed to be doing pretty good under the circumstances," said Whitmeyer, who spoke by phone to his niece Friday morning.

Offering $2,000 reward

There is a curved chain-link fence along the north side of the Wendy Drive overpass but not along the south side. If both sides of the overpass had been fenced, the incident might have been prevented, Whitmeyer said.

A California Department of Transportation spokesman could not comment Friday on why only one side had a fence.

Hammerand said Dalto's colleagues at the Probation Agency were saddened by the incident and hope whoever is responsible is brought to account. "Right now, our thoughts and prayers are with her and her family for her full recovery," he said.

While the CHP investigates the crime, Whitmeyer is looking for leads on who might have thrown the rock.

A former narcotics investigator for the Ventura County Sheriff's Department and a private investigator locally for 35 years, Whitmeyer went to the Wendy Drive area with three other relatives Friday afternoon, handing out fliers and asking for information about the incident, he said.

His family is offering a $2,000 reward for information leading to the arrest and conviction of whoever threw the rock.

Whitmeyer said the family appreciates the help it is getting from a nearby McDonald's, where "employees are handing out fliers to their customers and really cooperating."

That's very unusual'

Whitmeyer said he learned Friday there were attempted break-ins at the nearby Union 76 gas station on the same night Dalto was injured and on the following night, but he doesn't know if there's any connection.

Whitmeyer said he doesn't think his niece was specifically targeted, but he believes whoever threw the rock did it intentionally.

"That could have happened to anyone driving along Highway 101 at that time," he said. "I joined the Sheriff's Office in 1964, and I've never once heard of anything like this."

Thousand Oaks police officials said they were not aware of any other such incidents in the city.

Thousand Oaks Mayor Jacqui Irwin said, "Our thoughts are with Monica and her family, wishing her a full and speedy recovery."

Several Thousand Oaks residents who were at a shopping center near the overpass Friday said they were surprised to hear of the rock-throwing incident.

"I think it's a horrible thing," said Charlie Shaw, 55, a longtime resident. "That's very unusual. It's pretty benign around here."

To make an anonymous tip, contact Whitmeyer on his cell phone at 432-0054. Anyone with information about the incident is asked to call CHP Officer J. Howell at 553-0800.

— Staff writer José L. Sánchez Jr. contributed to this report.