Transbaykalia or Transbaikalia (both: trănsˌbĪkäˈlyə, trănzˌ–) [key], Rus. Zabaykalye zŭbĪkäˈlyĭ, region, SE Siberian Russia, extending from Lake Baykal to the Amur River, roughly equivalent to the contemporary Buryat Republic and Transbaykal Territory. It consists of plateaus and mountain ranges separated by wide, deep river valleys. There are gold deposits along the Vitim Plateau. Ulan-Ude and Chita are the chief cities of the region.