Penglai Peak is a granite ridge-like inselberg or mountain-island which is composed of medium-grained monzonitic granite from the early Cretaceous period (128 million years ago). The west, south and north sides of Penglai Peak are all faults which form sheer cliffs. The dense pine trees concomitant with rocks create amazing scenery just like a Chinese Penglai fairyland, so it is named Penglai Peak.