Geographic Features:

Sanyi Township lies at the center of Sanyi Terrace, between the Houyan Mountain and Guandao Range. The Guandao Range at the east is the highest area. With the Guandao Mountain and Jitu Mountain as divide, the upper stream of the Sihu River lies at the north, and the north branch of Daan River, the Liyu Stream (Jingshan Stream) watershed, lies at the south. Due to the cutting and abrasion as a result of water flow, the whole area is full of big and small hills, with an elevation of 400 meters. It is a typical brae area with many mountains and few farmlands. The plain comprises 10 percent of the area, and others are mainly mountains and hills. 

  The town area can be divided into the north part and the south part by the Sanyi Interchange of the Sun Yet-sen Freeway. The north part is the upper stream area of the Sihu River. It is a valley that opens up toward the north with limited farming area. The streets are built along the slope where the main habitats are situated. The south part is the fluvial plain of Daan River and its branch Liyu Stream. This fertile area is the main agricultural zone of the whole town. 

Guandao Range is situated at the east of the town. It starts with the Longchuan Mountain that lies at the south bank of Houlong River, and extends to Taiping Mountain at the north bank of Daan River. With a total length of 24 kilometers, the main peak Guandao Mountain with an elevation of 888 meters is the boundary of Sanyi with Tongluo, Dahu and Jhuolan. The whole ridge is formed by complicate green hills. The close by area is mainly brae with mild slope with an elevation from 300 to 800 meters. 

Huoyan Mountain at the west is the town border of Sanyi and Yuanli. It is the highest peak of Miaoli Hills, which comprises the area at the south of Houlong River, north of Daan River, west of Jianfeng Highway and extends to the Taiwan Strait. The side slope close to Daan River is characterized by its badland features. 

The Huoyan Mountain is 602 meters above the sea level and belongs to Touke Mountain Stratum. Its huge and thick gravel stratum is presumed to be the alluvium of the ancient Daan River transformed by violent orogeny. For the fast oxidation and eluviation, the gravel stratum is rich in ferreous and aluminous materials, and shows various colors among the deep valleys and conic mountains. At sunset, the landscape resembles dancing fire on the torches and it is thus named after its spectacular scenery.