>>49295116I know. Technically they also appear in Victory Road in GSC, but i think Victory Road is also made up and non-natural, and that like in the Safari Zone, they're introduced.
And since Rhyhorn can only be obtained in the Safari Zone in Hoenn, that means Sinnoh's Route 227 and 228 plus Stark Mountain's exterior are the first wild location Rhyhorn and Rhydon can be found. (Plus Route 228 has the Protector, like this route is the Rhyno Route. (And the music slaps))