"WASHBOARDING" - causes and mitigation
"Washboarding" is caused by driving too fast. Driving fast on a dirt road makes car tires hit small rocks and 'catch air' (when the car is bumpy and can even be thrown from the road) which causes small 'divots' in the road where the tires land. Driving slowly on the gravel rods will help mitigate this problem.
Creating a road crown, working to maintain a hard surface, and also using grade dips or water bars will also help prevent 'washboarding.'