In the north of the region is the Sailughem Mountains, also known as Kolyvan Altai, which stretch northeast from 49° N and 86° E towards the western extremity of the Sayan Mountains in 51° 60 N and 89° E. Their mean elevation is 1,500 to 1,750 m. The snow-line runs at 2,000 m on the northern side and at 2,400 m on the southern, and above it the rugged peaks tower some 1,000 m higher. Mountain passes across the range are few and difficult, the chief being the Ulan-daban at 2,827 m (2,879 m according to Kozlov), and the Chapchan-daban, at 3,217 m, in the south and north respectively. On the east and southeast this range is flanked by the great plateau of Mongolia, the transition being effected gradually by means of several minor plateaus, such as Ukok plateau (2,380 m) with Pazyryk Valley, Chuya (1,830 m), Kendykty (2,500 m), Kak plateau (2,520 m), (2,590 m), and (2,410 m).. Which plateau has the lowest elevation of Ukok, Chuya, and Kak?