A newly released California Highway Patrol report adds stunning detail to the Aug. 29 solo-vehicle crash involving indicted Sonoma investment adviser Ken Mattson, but perhaps raises as many questions as it answers.
Mattson hit the private security gate at the base of narrow Castle Road leading to his home at an estimated 60 mph, according to the only witness cited in the report. He plowed through a metal fence, a horse pasture and another fence, then continued approximately 200 feet down a ravine before smashing into a tree.
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When questioned by an officer following his airlift to Santa Rosa Memorial Hospital, the CHP report states, Mattson claimed he had no recollection of the crash — or the entire drive from his Orangetheory gym in Napa to the site of the wreck, a trip that normally would take about 25 minutes.
He didn’t regain consciousness until first responders were helping him out of his battered 2025 GMC Sierra after removing the driver’s side door.
Mattson was arrested outside the same gym in May, accused of wire fraud, money laundering and obstruction of justice.
The primary factor in the Aug. 29 crash is marked “unknown.”
There were no known external factors likely to have caused the crash. The weather was clear, the roadway dry at 2:15 p.m. that day, as reflected in the CHP report. Mattson was not using his cellphone at the time, the CHP investigator determined.
In one part of the crash form, investigators checked the box for “Impairment-Physical.”
According to a CHP collision investigation manual, that can refer to a wide range of maladies including everything from defective eyesight or hearing to paralysis, heart attack, epileptic seizure and diabetic coma.
“Explain in the narrative,” the manual instructs its officers.
The investigator did so to some extent, noting that he asked Mattson a series of pre-field sobriety test questions while the driver was still confined to a hospital bed at Memorial Hospital late that afternoon, and also asked him to perform “a limited series” of field sobriety tests. Mattson provided samples for a drug test, too.
It was determined he had not been intoxicated.
One lingering mystery is why first responders elected to call for a helicopter to transport Mattson to the hospital in Santa Rosa. His suspected injuries were “minor,” according to the crash report. His wounds are described as “abrasion to right hand, complaint of pain to head, neck, and pelvis.”
The determination to airlift the driver would have been made by attending fire personnel, Officer Marc Renspurger, who works in the CHP’s Napa office, told The Press Democrat.
The CHP investigator spoke to medical personnel at Memorial Hospital, who related that Mattson’s test results showed no sign of injury. The report indicates hospital staff was planning to continue monitoring Mattson, “to discover what caused (the driver) to lose consciousness.”
Mattson had no history of blacking out, according to the report. Stacy Mattson, Ken’s wife, told the investigator he had no history of mental health episodes.
The Mattsons live behind the security gate on Castle Road, in a 7,600-square-foot house on a 50-acre lot valued at around $7 million. The couple did not respond to messages. Ken Mattson’s civil attorney, Reno-based Micheline Fairbank of Fennemore Law, declined to comment.
The witness to the event was working on powerlines along Vineyard Lane — an alternate name for that stretch of what many call Castle Road. The worker watched as Mattson’s GMC accelerated through fences and field; the witness then contacted the owners of Bartholomew Estate Winery, whose property had become a crash site, and waited for the arrival of emergency personnel.
The damage to Mattson’s GMC is described as “major” in the accident report. A diagram shows damage points ringing roughly 80% of the vehicle.
Mattson has been in the spotlight since April 2024, when his longtime business partner Tim LeFever accused him of financial impropriety. Since then, the company they formed together, LeFever Mattson Inc., as well a separate company controlled by Ken Mattson, KS Mattson Partners, have been beset by lawsuits and bankruptcies.
Federal attorneys have accused Mattson of a Ponzi scheme in which he amassed a huge real estate portfolio by selling shares — some of them allegedly nonexistent — to hundreds of mom-and-pop investors.
He has pleaded not guilty and is free on $4 million bail, secured by a mix of real estate and cash.
On Wednesday, Mattson’s attorneys were scheduled to argue against federal prosecutors in a San Francisco courtroom, seeking to remove a 5,200-square-foot home in Piedmont from the bond agreement. Mattson wants permission to sell the house, which is owned by Stacy, in order to fund his criminal defense. It is scheduled for foreclosure sale in late October, with about $160,000 in overdue mortgage payments that Mattson blames on a tenant who shares the deed.
Magistrate Judge Alex Tse denied Mattson’s motion. Mattson’s team signaled their intent to raise the issue with the judge overseeing the criminal case, Jon Tigar, who has previously denied it on multiple grounds.
A government response filed in preparation for Wednesday’s hearing includes a letter sent by the law firm Hogan Lovells to Mattson’s criminal attorney, Randy Sue Pollock, that accuses Mattson of continuing to collect rents on properties owned by KS Mattson Partners — a company that was taken out of his control when it entered bankruptcy in June. Examples offered in the letter include a spa on Hwy. 12 in Sonoma that allegedly paid Mattson $4,000 in July and August, as well as a barber shop in Boyes Hot Springs and several other tenants whose checks were mailed to, but apparently never received by, KS Mattson Partners.
Another renter reported in July that Mattson had been loitering near the property, “making the tenant uncomfortable.”
Pollock’s response letter to Hogan Lovells adamantly denied the allegations.
You can reach Phil Barber at 707-521-5263 or phil.barber@pressdemocrat.com. On X (Twitter) @Skinny_Post.