Those Rocks Come from the HalfLife_Misc.VPK from Gmod directly according to hammer. My guess is that VPK is missing some textures maybe from a texture pack mod or something that messed with those rocks in particular. I'd recommend maybe verifying the integrity of your files for Gmod and that should hopefully reset that VPK if it is jacked up

verified game files, loaded map with no addons on. Emo rocks gone, thanks

that's why you shouldnt keep all your maps active at the same time ig

that is true! I didn't think of that, but I'm glad its fixed!