Abstract: In the winter of 1984, a cave-fissure deposit was first discovered in Yuanmou county,Yunnan. Seven species of mammalian fossils were recovered from the locality, i.e. Rodent in-det, Hytrix subcristata, Crocuta ultima, Cervus sp. (1), Cervus sp. (2), Bos (Bibos) sp., Cap-ricornis sp.. These are members of the " Ailuropoda-Stegodon fauna which is known fromsouth China during the Late Pleistocene. An age of 16540±1470 B.P. was determiaed by ra-diocarbon dating of the samples of fossil bones. The geological age is considered to be thelater part of the late Pleistocene as judged from the fauna and the 14^C test.
Xiao Midi is about 3km. to the south west of the village of Reshuitangcun of Yuanmou county and is situated on the top of Balan mountain. The maximum altitude is 1466 neters.The cave -issure deposit was developed in the Kunyan group of the Presinian period. Itwas formed by the convergence of the shear plane of a conjugated fracture.The cave in-clines NW and NNE. The dip angles are 80 and 60 respectively, resulting in an almostvertical fissure cave. The width is 5- -8 meters.The inclination is NNE and the thicknessis about 20 meters.
The deposit is fillded with a series of fragments of redbrown silts, clayey soils and in-cludes some brecia and lesser lime nodules. The wall of the cave is rough but there are nostalactite. The red crust weathering at the top is similar to that of T3, T4, T5 on the Long-chang River in Yuanmou Basin. It is interesting that there are more infant individuals inthe mammalian fauna.It raises doubts whether it is related to human activity although humanfossils had not been recovered in the site. So it may give a clue as to investigate paleoanthro-pology in future. The mammalian fauna consists of most of Artiodactyla, which reflect gras-sland- -style environment mainly.
This cave-fissure deposit was the first one discovered in Yuanmou. It is important because it fills the gap of late mammalian fauna in the area. It is the more recent geologicallysite in the Yuanmou Basin, being younger than Pliocene and early Pleistocene mammalian lo-calities previously recognized. It also adds to our knowledge of the cave fissure deposits beside the fluvial and lacustrine facies on the sedimentary face. It proviled new material for study of tbe palaeoecology and palaeoenvironment in the Yuanmou Basin.

Key words: Yuanmou, Yunnan; Mammalian fauna; Late Pleistocene; Cave-fissure deposit