Baer's mounds or ridges occur at the south of Caspian Lowland, forming areas of various size and configuration, the mounds' long axes are orientated east-west, the height is 2 to 45 meters, the width is 100 to 600 meters, the length is 0,5 to 8 km. They are known for more than 200 years, but their structure and genesis are still arguable points. A general geological section of a mound showing its rather complicate structure has been drawn on the basis of literature data. The mounds structure gives evidence on the beginning of their formation at inter-Khvalynian regression by eolian re-working thin cover of Lower Khvalynian sands (Q31) and of underlying chocolate-brown clays (also dated from Lower Khvalyn). During Late Khvalynian transgression the initial mounds were partly eroded, partly covered with Late Khvalynian sands. During the Post-Khvalynian regression the eolian processes resumed their activity at the North Caspian region and «completed» the Baer's mounds by deposition of the Upper Khvalynian deluvial-marine sediments at their non-eroded parts.