A preliminary CHP investigation indicates that Garberville CHP officer Thomas Adams crossed into oncoming traffic Tuesday, causing the crash that took his life in northern Mendocino County.

Adams, 24, had been on duty for a little more than six hours when the 2:15 p.m. crash occurred on Highway 101 near Piercy, just south of the Mendocino-Humboldt county line, the CHP said.

He was northbound on a right-hand curve in wet weather when he veered into the southbound fast lane and somehow spun so that his passenger side was exposed to oncoming traffic, Officer Erik Van Emmerik said.

A 2004 Toyota Tundra truck struck his passenger side, coming part-way into Adams' Ford Crown Victoria. The force of the impact likely caused his fatal injuries, though Adams was wearing a seatbelt, Van Emmerik said.

"If you combine the two speeds, it's quite an impact," he said.

Two men in the Tundra, driver Jeff W. Kidd of Perris and his passenger, Riverside resident Jared P. Geldhofbond, were taken to Jerold Phelps Community Hospital in Garberville for treatment of minor injuries to their hands and feet, authorities said. Both later were released, the CHP said.

Adams, a Fortuna native, had been with the CHP for about two years, working first in Oakland and transferring last fall to the Garberville station, which covers southern Humboldt County and northern Mendocino County, from Brooktrails outside Willits north.

He was one of 18 officers working the area, including six officers in the Laytonville resident post and 12 working the road out of the Garberville station, Van Emmerik said.

"It's a small office, so we're taking it kind of hard," he said. "It's going to be a sad day, that's for sure."

In a statement offering condolences to Adams' parents, Bruce and Karen, Gov. Jerry Brown said flags at the Capitol would be lowered to half-staff in honor of the officer.

"Thomas spent the last two years as a Highway Patrol officer keeping Californians safe from the Bay Area to the Northern Coast," Brown said. "His courage, service and sacrifice will not be forgotten. Our thoughts and prayers are with those grieving this tragic loss."

Adams was working a 6 a.m. to 6:30 p.m. shift and was on patrol near Piercy when he died, Van Emmerik said.

Dispatch records indicated he was not en route to a specific assignment, and it remained unclear if he had seen a speeder or observed some other traffic violation, Van Emmerik said.

It was unknown if he was using a cell phone or computer, Van Emmerik said.

Authorities, who were hampered by rain during their their investigation Tuesday night, expected to contact additional witnesses Wednesday to determine whether Adams had activated his lights or siren before the crash, Van Emmerik said.

The CHP's Redding-based Multidisciplinary Accident Investigation Team, or MAIT, which specializes in accident reconstruction and speed and position calculations, also was expected to arrive and conduct a separate investigation, he said.