"WASHBOARDING" - causes and mitigation
"Washboarding" is caused by accelerating and braking on the roads - or going too fast. Moving too fast creates tires to hit small rocks and 'catch air', 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.