In an incident remarkably similar to a roadside sexual assault last month, a young woman alerted authorities that a man pulled her over Thursday night on the same stretch of rural Bennett Valley Road outside Santa Rosa.

The woman stopped her car and was approached by a man in a hooded sweat shirt and ski mask before she sped off and used her cell phone to call for help, Sonoma County Sheriff's Lt. Scott Dunn said.

The incident shortly before midnight mirrors in many respects a Nov. 18 sexual battery case in which a 19-year-old Santa Rosa Junior College student was assaulted while driving home from a night class.

In the earlier case, the woman was between Santa Rosa and Glen Ellen, near Old Bennett Ridge Road, when a motorist flashed his lights behind her, then pulled alongside in an apparent effort to get her to stop, authorities said.

When she pulled to the side of the road near Enterprise Road, a young man approached her car with his sweater pulled up over his lower face and nose and told her there had been a motorcycle crash that she should report.

But then he told her to hang up the phone, threatening to harm her if she did not, and sexually assaulted her as she sat in her car, the Sheriff's Department said.

Thursday night's incident occurred at 11:51 p.m., again near Enterprise Road. When the woman, who is in her early 20s, called 911 for help, she was directed to a safe location, where deputies met her and took a report of the incident.

Dunn said the situation is particularly alarming given reports of a similar incident in Rohnert Park, although he did not have details.

He said it's possible a single suspect is involved -- someone who "is obviously a potential danger to the individual he's trying to stop."

He also said the reports are alarming because of the possibility of other instances in which victims have been too afraid or embarrassed to make reports.

Deputies are stepping up their patrols of the area but advise motorists never to stop in suspicious circumstances and to immediately call 911 if a cell phone is available.

Otherwise, they should drive to a safe, visible location, such as a law enforcement or fire station or highly visible business, stay in their locked vehicle and continuously honk the horn to attract help and thwart an attack.

Anyone with information about the incidents should call the Sonoma County Sheriff's Department at 565-2650.

You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat .com.