The bus driver and nine passengers were taken to a local hospital Sunday night after the crash, the Los Angeles Times reported.
The bus was carrying 18 people from Los Angeles to the Casino Pauma.
The California Highway Patrol said the bus' brakes failed, causing the bus to careen of the the road and crashed into trees and a boulder.
Most injured passengers had "various complaints of pain," CHP said.
The incident is still under investigation.
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