Region and Terrain
This township is located in the northeast end of Kaohsiung County, with Yushan Mountain Range on the east and adjacent to Liouguei Township; in the south is Shanlin Township; the north is Sanmin Township; where as the west border is the Dawushan Neiwushan mountain, which is adjacent to Nanhua Township of Tainan County. The distance between the east and the west is 5.3 km, and 22.61 km for the distance between the north and the south, with an altitude of 252.06 meters (based on the No. 428 benchmark in front of Jiasian Primary School at Sian Village of Jiasian Township). While on the north side, there is the long and narrow Nanzihsian River formed through Siaolin Fault, which flows through this township to Shanlin Township and Cishan Town, then converge with Laonong River and Gaoping River. The entire area for the township is 124.0340square kilometers.
Geology
The rock formations in Jiasian region are mostly Miocene sedimentary rocks, especially Guandaoshan sandstone and Shihlioufen shale. Guandaoshan sandstone is distributed in the Westside mountain ridge of Nanzihsian Rievr (Cishan River) at the south of Siaolin. Besides the Nanjhuang Formation at the top of Neiying mountain ridge on the east side of Nanzihsian River, the rest are Shihlioufen shale (used to be known as “Jiasian shale”). There is the north-south Siaolin Fault close to the border of Neiying mountain, with parallel arrangement of Shihjhangli syncline, Jiasian anticline and Aliguan syncline etc., and the oblique axis extending from the north to the south in the proximity of Siaolin all disappeared in the neighborhood of Jiasian. With Nanzihsian River in between Aliguan syncline, Dawushan and Neiwushan, there is extreme variation for the terrain within the 5.3 km distance between the east and the west of this township; there are numerous folds, continuous mountains and hills with very little level ground. The few terrace deposits formed at Datian, Sihde, Jiangpu, Aliguan, Neicyongjiao, Wulipu etc., in addition with the scarce alluviums on both sides of the Nanzihsian River became the main land for cultivation in this township.
Climate
Due to the fact that this township is surrounded by mountains, there are abundant trees and rainfall, which offer the comfortable climate of cool in the summer and warm in winter, as if it is springtime all year round. There is more rainfall during the period from early summer to early autumn, with the most in August on average, and the least in December.