Modder 'jd941' created a Photogrammetry mod that updated the textures of the rocks found around the original Skyrim. Now, modder 'LupusHegemonia' has made the same mod available in the Special Edition version of Skyrim.
LupusHegemonia has released two versions of the mod, the first being the original authors creation "This is the author's original 4K-4K (and some 8K-8K too! ) textures files - defuse/normal maps/pumping maps etc." The second being a creation of his own "This is my personal version of the textures. I made them quite much de-saturated and most of them in grey-tones. Also, I added more grunge surface to most of the rocks' textures/normal maps. My version in 4K-2K resolution."
If you are interested in updating the textures of your rocks in Skyrim: Special Edition, here is the direct link to the Nexus Mod page where you can find many screenshots of the terrain.