The Nankang Hills stretch across the Taipei Basin as a straight finger of low sandstone peaks 140-370 meters high. Their highly uneven topography, carved out by the abundant local rainfall, has meant that despite lying cheek by jowl with the city, they have been spared destructive overdevelopment and have been able to maintain a basic forest environment. The hills 'great diversity of microenvironments creates a paradise for ferns.
豐沛的雨水，在三百多公尺的南港山砂岩地質上雕琢出多座小山，如手指在台北盆地上一字排開，地型「凹凸有致」、起伏多變，使得南港山雖身處過度開發的台北臥榻之旁，卻能僥倖逃過人類全面性的摧毀，維持著起碼的森林型態。