The concept of “Yanshan movement” (“Yenshan movement”) had been put forward by Professor Wong W H for more than 90 years. Endless debating exists after the concept was put forward. This paper reviewed the concept and corresponding logical questions firstly. Mr. Wong divided the movement into three stages: the A (the beginning), the middle (the volcanicism) and the B stage. The unconformity of the A stage exists between the upper volcano rock series and the coal measure strata. Bottom of the upper volcano rock series is a suit of conglomerate, for example, the Longmen—Jiulongshan Formation in western Hills， Beijing, and the Haifanggou Formation in Liaoning province. Mr. Wong attributed the conglomerate to the A stage. A question puzzled by Wong W H was the temperal and spacial relationship between the conglomerate and the volcanics. This is an important issue, but frequently escaped the attention by followings. Wong W H did not distinguish the difference between the concept of “Yenshan movement” (“Yanshan movement”) and the “Yenshanian movement” (“Yanshanian movement”), which leads to misunderstandings in following studying. After clarifying the original concept, through a drilling and an exploratory trench in Yanchi town, Mentougou county, Western Hills, this paper firstly discovered a suit of turf in 12m thick under the Jiulongshan Formation. Under the tuff, a suit of calcareous conglomerate in 2m particle size is unconformity with the Cambrian strata, which is just the unconformity of beginning of Yanshan movement. U-Pb dating of the tuff yield the eruption age of 154Ma and the inherited age of 161Ma. The former represents the maximum age of the Jiulongshan Formation and the later responses to the earliest volcanic eruption of the A stage in Western Hills，Beijing. Finally, this paper points out that the diachronism of the three unconformities in Western Hills. The unconformity under the Jiulongshan Formation and the Longmen Formation will converge to the main unconformity under the Tiaojishan Formation. The Longmen—Jiulongshan Formation and the Tiaojishan Formation are at the same time to different strata unit in western Hills.