How was the Qinghai region connected to Tibet in prehistoric times?

In prehistoric times, the Qinghai region was closely linked to Tibet through migration and cultural settlement. Specifically, the cultivable land near Koko Nor is believed to have been the original home of the tribes that eventually settled in Tibet.1

The region, known as Amdo in Tibetan, has historically been considered part of Tibet. Archaeological evidence also highlights the presence of the Qijia culture in the area during the Neolithic period, which extended into Qinghai and demonstrated unique northern Eurasian influences, such as distinct pottery styles and the use of early copperware.12