(Reuters) - The search for a prominent automotive journalist missing since last week in northern California’s gold country has focused on a river where his motorcycle, clothing and other belongings turned up, but no foul play is suspected, authorities said on Thursday.

David Gordon Johnson, 43, disappeared while on his way home to the Sacramento area from a long-distance motorcycle ride that friends said was meant as a test drive for a magazine article he planned to write.

The motorcycle was found parked at a boat launch along Mokelumne River in rural Calaveras County, about 60 miles (97 km) southeast of Sacramento, where he presumably had stopped to rest, the county sheriff’s office said in a statement.

The key was left in the ignition, with his helmet and gloves on the seat, it added.

Johnon was reported missing by his fiancee, and a search began on June 7, according to the statement.

The effort was expanded the next day to include boats, ground teams, a police helicopter and drones combing the riverbanks for several miles along both sides of the swift-flowing Mokelumne, it added.

Some of Johnson’s clothing and personal items, including his cell phone, laptop, and two jackets were later located by ground searchers, and a tracking dog followed an apparent scent trail to the water’s edge.

On June 9, the search was widened with additional scent-tracking dogs, with more of Johnson’s clothes found at the spot where he was believed to have taken a “selfie” photograph sent to a friend days earlier. A new scent trail picked up by dogs again led to the river, the sheriff’s office said.

“With all evidence pointing towards Mr. Johnson having gone into the Mokelumne River for unknown reasons, and with no evidence of foul play, search efforts have continued in the subsequent days along the river’s edge,” it said.

The search will continue for the rest of the week, it said.

Media outlets have said Johnson’s last known communication was a June 5 text message to his fiancee, Jaclyn Trop, who was quoted telling the automotive magazine Car and Driver, “I just hope he’s figured out how to stay alive.”