Terrace development characteristics of Dashi River valley in Western Hills of Beijing

Terrace is developed in Dashi River valley. It is mainly bed rock seated terrace. The first to fourth terraces are relatively well developed from Chenjiatai to Hongmeichang in lower reaches. Only one terrace is seen in upstream Zhuanghutai Village. The sediments are mainly gravels and sands in upstream reaches. They are sands and clays in lower reaches. The dating of fourth terrace in Hongmeichang Village yielded an age of 567±56ka, suggesting that the Dashi River was formed in Mid-Pleistocene. The four terraces were formed by uplift of New Tectonic Movement. The longitudinal river slope is 7.71‰ from the river mouth of Xinkaikou Village to Longmentai Village in upstream reaches. Since 600ka, the Hill in Dashi River valley has been uplifted by 0.96mm/a.