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西乡县境内的大巴山为大巴山西段的最东端,汉南隆起的最东部,古生代地层为典型的地台型沉积。这里二迭纪地层发育齐全,层序清楚,化石丰富,蜒类、珊瑚类、腕足类及头足类等海相动物混生,顶底还偶而可见古植物化石。岩性、岩相和南郑梁山颇为相似,除顶底及中间有不厚的页岩外,几乎全为浅海相碳酸盐岩建造,总厚度约350米左右。分布在白勉峡——三郎铺——堰口——峡口一线之南,呈NE——SW方向延伸,大致向SE倾斜的单斜构造,与三迭纪灰岩共同构成了牛岭山、午子关、盖仙寺至贯山的一条高耸的刃状山岭,阻隔南北,依靠峡谷相通,地势甚为险要。在此线之南,另一主要由三迭纪地层构成的向斜的两翼仍有二迭纪地层零星出露。
The Daba Mountain in Xixiang County is the easternmost part of the western part of Daba Mountain and the eastern part of Hannan uplift. The Paleozoic strata are typical platform-type sediments. The Permian strata here are well developed, with clear sequence and abundant fossils. Marine animals such as serpent, coral, brachiopods and cephalopods are mixed with each other. Lithology, lithofacies and Nanzhengliangshan quite similar, in addition to the bottom and the middle of thick shale, almost all shallow marine carbonate rock construction, the total thickness of about 350 meters. They are distributed in the south of the Bimianxia - Sanlangpu - weir - Gap line, and have a monoclinic structure extending in the NE - SW direction and inclined to the SE. Together with the Triassic limestone, they constitute the NiuLingshan, Wuzi Guan, Gaoxian Temple Zhiguanshan a towering blade-shaped mountain, blocking north and south, relying on the same canyon, the terrain is very important. On the south of this line, two other synclines, mainly composed of Triassic strata, are still sporadically revealed by the Permian.