As i can remember rust has an inbuild fuction to place a rock or a mountain or whatever due to a map bug players can see through it.
But for the love of .. i cannot find this command does anyone know ?

the command is: spawn

Thank you @ninjaT for future reference for anyone the command fully is

spawn admin_rock_clutter_medium_d
spawn admin_rock_formation_medium_a
spawn admin_rock_formation_small_c
spawn admin_rock_quarry_small_a​

it's a shame you can't link search results on these goofy forums, search results are a pain in the ASS https://umod.org/community/rust/39501-admin-spawnable-rocks I usually tell ppl to rtfm or use the search, but here I get it, it's so bad!