A 49-year-old Petaluma man severely disabled in a motorcycle crash was found Thursday night in St. Helena, a day and a half after he was last seen by family members, Petaluma police said.

John Wirth has a severe brain injury that leaves him unable to care for himself and was considered at risk, police said.

A cell phone that he carries but does not use was detected Thursday night in the area of Jameson Canyon Road and Interstate 80 between American Canyon and Fairfield, police reported.

It was unclear how Wirth, who uses a bicycle, might have traveled so far, authorities said.

When Wirth was found in St. Helena, he did not have his phone, Petaluma police said in a news release late Thursday night. Officers were with Wirth and were working on reuniting him with his family, the release said.

Wirth left home around 7 a.m. Wednesday on a red Pacific bicycle and was reported missing around 7:30 p.m. when he had not come home.

He is easily confused and unable to manage many normal functions because of traumatic brain injury suffered in the crash, police said.