There was a theory last year that the potholes on our dirt road were caused by snow plows. I researched the literature which reported that potholes are caused primarily by water and the lack of a crown in the road. Yes, a snow plow can occasionally hit a large rock sticking out of the road and remove it, with the resulting depression being vulnerable to water and grow to a large pothole. But this year the snow plows only plowed twice (less than a foot each time), and yet abundant new potholes have appeared on the road -- in my judgment more than last year, thus proving conclusively that potholes in dirt roads are not caused predominantly by snow plowers.
Click here for a good article on gravel/dirt road troubleshooting and maintenance.