I noticed there are 5 different habitats for Ground types
>Deserts (Sandshrew, Trapinch, Sandile, Hippopotas)
>Caves (Diglett, Gible, Drillbur, Onix)
-Swamps/Marsh (Wooper, Barboach, Palpitoad, Marshtomp, for some reason that's not Gastrodon case)
-Mountains/Cliffs (Gligar, Cubone, Geodude, Larvitar)
-Wild plains (Phanpy, Rhyhorn, Nidoking, Nidoqueen, maybe Mudbray)
I could add ruins for Baltoy and Golett, and even seashores for Gastrodon and Palossand