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黄河三门峡水库北岸的山西省平陆县黄底沟剖面，较完整地保存着古三门湖湖相沉积记录。经磁性地层研究结果表明，古三门湖沉积起始于吉尔伯特负极性时中期，大约在５ＭａＢＰ；结束于布容正极性时晚期，结合热释光年龄，大约在１５０ｋａＢＰ。鉴于古三门湖沉积地层从晚第三纪上新世早期延续至第四纪中更新世晚期。因此，我们将这套地层统称为三门群，并据其岩性特征自上而下划分为三段，上段以砂层为主；中段以粘土层为主；下段为底砾石层。黄底沟剖面是已知的记录古三门湖发育起始时间最早、结束年代最晚的地层剖面。
Huanglonggou profile of Pinglu County, Shanxi Province, on the north bank of the Sanmenxia reservoir of the Yellow River, has a relatively complete record of the sedimentary records of the ancient Sanmen lacustrine facies. The magnetic stratigraphic study shows that the deposition of Guansanmen Lake started from the mid-Gilbert negative-polarity period of about 5MaBP, and ended at the late stage of positive cloth capacity, combined with the thermoluminescence age of about 150kaBP. In view of the ancient Sanmen Lake sedimentary strata from the late Paleocene to early Quaternary Late Pleistocene. Therefore, we collectively refer to this group of strata as the Sanmen Group, which is divided into three sections from top to bottom according to its lithological characteristics. The upper part is mainly composed of sand layers. The middle part is mainly composed of clay layers. The lower part is the bottom gravel layer. The Huangdi gully profile is known to record the earliest onset of development of the ancient Sanmen Lake and the late stratigraphic section of the end.