Fly-tippers dumped more than 100 bags of clay, rocks and other rubbish on Gelligaer Mountain.
Following the two separate incidents , Caerphilly County Borough Council has appealed to the public for help.
The first dumping was discovered during the early hours of Wednesday October 17 and the second on Friday October 19.
The first involved approximately 45 full bags of abandoned clay, rock and various materials while the second incident saw approximately 60 bags of similar materials strewn across the road.
Council workers cleared the mess, but there are concerns the fly-tippers will strike again.
Cllr David Poole, cabinet member for community and leisure said: “Fly-tipping is wholly unacceptable in any way shape or form, but this instance is extremely alarming and irresponsible due to the volume of materials being dumped in such a dangerous location.
“As we approach winter the occurrence of rain, mist and fog is increasing, and should an innocent driver have come across this debris in the dark of the night, it would almost certainly have resulted in a serious accident.”
Any members of the public with information relating to these incidents are urged to contact Caerphilly StreetPride on 01443 866 566.