During the Triassic, the sedimentary characteristics of the Gonghe and Bayan Har basins, located on both sides of the Buqian- Anemaqen mountain range, are closely related to the evolution of the Buqian- Anemaqen Ocean, a branch of the Paleo- Tethys Ocean. Although previous studies have extensively focused on the eastern parts of these basins, research on their central and western parts is relatively weak. This paper selects the Longwuhe Group in the Gonghe basin and the Bayankalashan Group in the Bayan Har basin as research subjects. Through comprehensive analysis of their sedimentary sequences, paleocurrent directions, sedimentary provenances, and prototype basin types, combined with existing regional geological data, this study aims to discuss the closure timing of the Buqian- Anemaqen Ocean. Our findings suggest the following: ① Triassic sedimentation in the Gonghe basin reflects its function as a back- arc basin, receiving sediments from different source areas. North of Maqin, sediments were derived from the Eastern Kunlun and Qaidam regions, supplying the Gonghe, Guide, Zeku, and Henan County areas. North of Maqu and east of Gonghe, Guide, Zeku, and Henan County, the northeastern Qilian Mountains constituted the dominant sediment source. South of Maqin and Maqu County, the Buqian- Anemaqen region itself acted as the primary sediment source. ② During the Triassic, the Bayan Har basin existed as a remnant ocean basin, with its main sediment provenance derived from the northern Buqian- Anemaqen. ③ The Buqian- Anemaqen region had already uplifted and transitioned into an erosional area prior to Triassic sedimentation. This uplifted region subsequently served as the main provenance for the basins.