Amdo

"The traditional Tibetan region of Amdo is located on the northeast corner of the Tibetan Plateau. Though most of Amdo lies in modern day Qinghai province, large regions also are located in southwestern Gansu and northern Sichuan provinces. Amdo is broken up into 8 prefectures: Golog, Malho, Tsolho, Tsonub, Tsobyang, Tsoshar in Qinghai province, Ganlho in Gansu province and Ngawa in Sichuan province. Roughly 1.5 million Tibetans live in Amdo which accounts for over 25% of the total Tibetan population."

http://kekexili.typepad.com/life_on_the_tibetan_plate/2009/01/tours-of-amdo-tibet.html