Both distant Tianshan suture zone and proximal local horsts are possible sources of Upper Permian sedimentary rocks exposed in the BogdaMountains. The Abundance of volcanic grains indicates the former was the main source. Paleocurrent direction further suggests the sole main source located to the south, which is consistent with that the Tianshan suture zone is the main source. Sandstone petrographic data show two petrofacies, A and B (QFL = 5:7:88 and 32:8:60). The change from A to B suggests that the Tianshan suture zone evolved from an undissected to a transitional arc during unroofing; upsection increase of phaneritic clasts (from 3 to 14%) in conglomerates supports the interpretation.