Although study of this period of history is complicated by the absence of contemporary records, the discovery of archaeological sites has enabled a succession of Neolithic cultures to be identified along the Yellow River. Along the central reaches of the Yellow River were the Jiahu culture (c. 7000 to 6600 BCE), the Yangshao culture (c. 5000 to 3000 BCE) and the Longshan culture (c. 3000 to 2000 BCE). Along the lower reaches of the river were the Qingliangang culture (c. 5400 to 4000 BCE), the Dawenkou culture (c. 4300 to 2500 BCE), and the Yueshi culture (c. 1900 to 1500 BCE).