Determining who’s at fault for a car accident can be a bit tricky. There are differences between who caused the collision and who is legally at fault. Determining who is at fault will affect whose insurance will be used to pay for damages to any vehicles involved, as well as which driver will be held responsible for any personal injuries sustained.
Normally, the driver who initiated the accident would have to pay for all the damages they caused. However, there is a complicated system of determining fault. There is a chance of having a percentage of the blame distributed to each driver that contributed to any part in causing or failing to avoid the collision -- in California, this is known as comparative negligence. This means that there may be different monetary obligations for each party involved.
In general, any driver who violates traffic laws is subject to facing consequences for their actions. If one of the drivers is given a citation for running a light/stop sign, speeding, or any other violation, they will potentially be at fault and carry the most liability.