The tectonic depression of the so-called Valley of the Gobi Lakes containing a series of former lake basins stretches in WNW-ESE direction between the bordering old Khangay massif in the north and the young Gobi Altay ranges in the south. All basins are endorheic and of different size each of them nourished by a big Khangay river. Except the lakes of Böön Tsagaan Nuur and Orog Nuur all basins are dried out today. Former lake levels documented by calcareous silty sediments and beach ridges at different highs above the bottom give evidence of pluvial periods of different intensity during the younger Pleistocene and the Holocene. Special studies were carried out around the basins of Orog Nuur and the adjacent small Taatsyn Tsagaan Nuur and, for comparison, the Ulaan Nuur east of them.
The main results are as follows: The 60m-level of the Orog Nuur as the highest one detected and dated to MIS 4 is connected with the 40m-level of the Taatsyn Tsagaan Nuur indicating a single lake at that time which invaded the south-bordering Nugyn Els dunefield. This has formed by accumulation of fine sand predominantly deflated from the periodically dried out lake basins.
The main river terrace of the Taatsyn Gol draining to the Taatsyn Tsagaan Nuur and the comparable terraces of other Khangay rivers obviously correlate with this highest lake level. In the Orog Nuur basin two younger palaeolake-levels at 20m and 8m above the modern lake level are well documented. Their preliminary ages are Late Glacial and Mid-Holocene respectively.