Taipei Basin
The Dahan River once flowed north through the area of Taoyuan City to empty into the Taiwan Strait about west of the mouth of the Tamsui River. The Taoyuan Plateau is the ancient alluvial fan of the Dahan River, created by sediments eroded from the mountains. About 30,000 years ago, tectonic movement caused the Taipei Basin to drop in elevation, and the Tamsui River system captured the Dahan River and caused it to flow northeast. As a result the Dahan River cut a canyon through the alluvial sediments for more than to reach the new lower elevation. The former channels of the Dahan River remain as "beheaded" streams that flow only seasonally across the plateau.