Today Johto is primarily a land of plains, its only major peak of Mount Silver located at its far eastern edge. However, Bronze Age Johto was known in foreign records for its many mountains and a pokemon called Larvitar with a thick hide which could be ground up into Hard Stones. Mount Silver in that era was twice its current height and bordered a Mount Gold and Mount Crystal, with countless smaller peaks and valleys nestled in between.
Yet even these enormous mountains were much smaller than they had been in prehistoric times. The reason for their cataclysmic disappearance was neither the chaos of nature called plate tectonics, nor the savage disregard of Man for his environment, but the evolution of the tiny Larvitar. Stories of a single Larvitar eating a whole mountain are either exaggeration or use a significantly more generous definition of "mountain" than current science, but it was true that an individual Larvitar could devour a reasonably large hill; over a few generations, every mountain in Johto is and was doomed.
It is lucky for all who love Mount Silver, or even Larvitar themselves, that they take a thousand years in the wild to reach maturity. Their numbers have dwindled dramatically, both from starvation and other mountain pokemon who feared the fate of their brethren throughout Johto, who now live shortened lives and only reach a fraction of their potential. Although Mount Silver is still shrinking, any trainer brave and powerful enough to venture in, and lucky enough to spot one, can still find a Larvitar. These pokemon have amazing potential, but even the greatest should be warned, for they cost a small fortune in soil to feed!