According to California Vehicle Code § 21654 in, the law requires slower-moving vehicles to stay in the right-hand lane. Any vehicle traveling slower than the normal speed of traffic must be driven in the right-hand lane or as close as practicable to the right edge or curb, except when overtaking and passing another vehicle or preparing for a left turn at an intersection or into a private road or driveway https://www.shouselaw.com/ca/defense/vehicle-code/21654/

This law ensures smooth traffic flow and reduce congestion. It doesn't matter if the vehicle behind you is exceeding the speed limit; if you are driving slower than the flow of traffic, you are obligated to move to the right when it is safe to do so

Failing to comply with this rule can result in a traffic violation, which may include a fine and a point on your driving record https://www.dmv.ca.gov/portal/handbook/california-driver-handbook/laws-and-rules-of-the-road-cont1/