The unidentified woman was driving a 1999 Toyota on northbound Interstate Highway 680 approaching Calaveras Boulevard at about 10:05 a.m. when she lost control of her vehicle, according to Thibodeau.
A witness reportedly saw the Toyota begin to fishtail and then veer to the right across all lanes of traffic, according to Thibodeau.
The Toyota then continued down an embankment on theright side of highway 680 and rolled onto its right side, coming to rest when it hit two palm trees at the bottom of the embankment, Thibodeau said.
One of the palm trees penetrated the roof of the Toyota and impacted the woman, who suffered fatal head trauma and other injuries, according to Thibodeau.
The Toyota came to rest at the bottom of the embankment, about 300 feet north of the Calaveras Boulevard offramp.
Emergency crews and a tow truck blocked the eastbound Calaveras Boulevard offramp for about two hours this morning, and a Sig-alert for the highway was issued.
The cause of the accident is under investigation, and toxicology reports to determine if alcohol or drugs were involved in the accident have not been completed, Thibodeau said. The coroner will also test to see if a medical condition may have been involved in the accident, he said.
The woman's identity has not been released pending notification of next of kin, Thibodeau said.