The bus was moving about 45 to 50 miles per hour as it took passengers from a concert in Mountain View to Santa Cruz on Highway 17 late Friday, when the door to the bus somehow opened during the fight and both women fell out, said Officer D.J. Sarabia.
The woman who died was run over by the bus, Sarabia said. She was pronounced dead at the scene.
An official at the Santa Clara County Medical-Examiner-Coroner's Office said the woman had not been identified. The patrol did not release the name of the injured woman, but said she was hospitalized with moderate injuries.
About 12 to 15 people were on the bus, but investigators were having trouble sorting things out because the passengers were "highly intoxicated," Sarabia said.
"Many were incoherent or didn't want to cooperate," he said.
Investigators were not even sure of the exact number of passengers because some people ran from the scene after the incident, he said.
"The only thing we know that these two women were in some sort of altercation," Sarabia said.
The bus, operated Party Bus of Santa Cruz, was towed to an impound yard, where investigators were trying to determine how the door opened. There are two ways to open the door, either by the driver pulling a lever or by pulling an emergency device near the door, Sarabia said.
"The driver obviously didn't open the door," Sarabia said.
No citations have been issued, and no arrests have been made.
Party Bus of Santa Cruz has been in business for six years and rents its buses for weddings, concerts, bachelor parties and other events, according to its website. A person who answered the phone at the company declined to comment.
Following the crash, officers temporarily shut down a section of Highway 17, Sarabia said.