It is also very probable that the Tannu-ola Mountains north-east of Ubsa-nor„ and the Khangai Mountains between Ulyasutai and the upper Orkhon, both running W.N.W.
On this vast upper terrace even the bottoms of the river valleys are at altitudes of 4200 to 5500 ft., with one single exception - the narrow gorge of the Khua (Khi)-khem, or upper Yenisei; while the highest pass across the Tannu-ola Mountains is 7090 ft., though the others are much lower.
In the Khangai, the Tannu-ola, and on the slopes of the border-ridges.
Are covered with forests, the Tannu-ola and the Khangai Mountains have woods on their northern faces only, and the Ektagh Altai is quite devoid of woods, even on its northern slope.
Coal is known to exist to the southeast of Kobdo, in the Tannu-ola, and in the basin of the Yenisei, but its age is unknown (fresh-water Jurassic ?).