SAN FRANCISCO — A tour bus carrying visitors from Yosemite National Park was traveling at an unsafe speed when the driver lost control and crashed on a mountain road, leaving 16 people injured, the California Highway Patrol said Sunday.

The bus was about six miles outside of the south entrance of the park when it went off Highway 41, a winding mountain road when it crashed about 6 p.m. Saturday. It came to a stop when it hit a tree, CHP Officer Scott Jobinger said.

Fifteen passengers and a tour guide suffered minor to moderate injuries.

"At this point the cause was the bus was traveling at unsafe speed and went off the road," Jobinger said. He said the accident remained under investigation to determine if other factors played a role.

CHP Sgt. Edward Green told the Fresno Bee that the impact of the crash caused several passengers to be thrown to the driver's side of the bus, with the bus stopping when it hit the tree.

"If the tree wasn't there to stop the bus, it would have continued down the ravine," Greene said.

The 15 injured passengers, described as mostly elderly, and a tour guide were taken to local hospitals for treatment.

Four of the injured were treated at Community Regional Medical Center, and four were treated at Clovis Community Medical Center, said Jennifer Avila-Allen, a spokeswoman for the hospitals. All but one at Community Regional had been released, she said. The conditions of the others, taken to a different hospital, were not known.

The bus was towed to an impound yard where it will be inspected to see if any mechanical problems may have contributed to the crash, Jobinger said.

The bus driver, identified as Changefeng Liu, 49, of Fremont, Calif., was the only person on the bus who was not hurt. He has not been arrested, and alcohol is not believed to be a factor in the crash.

Investigators have not determined the exact speed of the bus at the time it went off the roadway, but the scenic highway has sharp curves where the speed limits drop to 35 miles per hour, Jobinger said.

The bus is operated by Seven Happiness Tour & Charter, a Burlingame, Calif.-based company that specializes in providing tours to the Chinese-American community, said Charles Wu, who works at the company and answered the phone at its headquarters Sunday. He said the owner would not be available to comment until Monday.

"Most of them (passengers) were Chinese people from the Bay Area," Wu said.

Wu said he had not talked to the bus driver since the crash and have few details about the incident, but said Liu had worked for the company for about six years.

Liu could not be reached for comment.

The tour bus company, which operates six motor coaches and six mini-buses or vans, has not had any crashes in the last 24 months, according to records with the Federal Motor Carrier Safety Administration.