The formation of the Hai'an Range did not take place in Taiwan, the northern Luzon arc instead. It is mainly composed of calc-alkaline volcanic formations. In late Miocene age where sea level is high, flysch-like Plio-Quaternary sediments deposited forming layered sedimentary rocks. Due to the compressional force generated by plate movements, the Hai'an Range rock layers experience folding, thrusting and uplift.