California Motor Vehicle Code 21661
If you are driving on a narrow roadway, you must be aware of other drivers, and yield to them for safety. California Vehicle Code 21661 states that the driver traveling downhill must pull over and allow the driver driving up hill to pass. If there is no room for you to pull over, you must backup enough so the driver facing uphill has room to pass.
A narrow roadway is one that is not designed to allow two cars to pass each other safely. These roads are usually private drives, or rural roads where there is not enough room to widen the road to allow for two cars.
If you are going downhill, you must pull off the road as soon as it is safe to do so, to allow the approaching car to pass safely. The car traveling downhill is in a better position to pull over than the one traveling uphill. The driver going downhill can see farther, has a better vantage point to see where there is a safe spot to pull over, and will be able to pull back safely onto the roadway when safe. The car facing downhill also has more control of their vehicle when backing up to allow for safe passage. The car going uphill does not have these advantages.
If there is enough room for the approaching car to pass safely, you do not need to pull completely off the road. Just pull over and give the ascending vehicle enough safe distance to pass. The ascending vehicle should have at three-fourths of the roadway available to them.
Recreational vehicles and larger trucks are usually not allowed on narrow roads. They cannot safely backup to allow other cars to pass. Be sure to check with your local authorities if you are unsure whether your RV is allowed to drive on rural roads.