蔡家沟遗址是蔚县盆地东北部吉家庄台地一处重要的中更新世旧石器遗址，2019年9-10月发掘出土349件石质标本与569件动物化石。根据地层中的哺乳动物化石推测遗址年代为中更新世，²⁶Al/¹⁰Be埋藏测年结果为0.47±0.13 Ma至0.64±0.21 Ma，属中更新世早期。蔡家沟遗址A地点石制品原料以火山岩为主，另有少量硅质白云岩、燧石等；石制品类型包括石核、石器、完整石片、碎片、断块、石锤等；石核剥片与石器修理均以锤击法为主，完整石片以V型和VI型为主，显示次级剥片特点；石核保留的剥片片疤数量较多，显示较高的石核利用率，部分盘状石核的存在反映出古人类较高的技术组织能力。从出土动物化石的保存状况与痕迹分布来看，古人类活动对该遗址动物骨骼的改造作用占据主导地位。蔡家沟遗址A地点的石制品具有原料搬运距离较远以及石核剥片策略高效等特点，相较盆地内早更新世遗址具有明显的进步性，对探讨泥河湾盆地中更新世古人类技术特点与行为演化具有重要意义。

The Nihewan Basin (senso lato) comprises three subbasins named Datong, Yangyuan, and Yuxian Subbasins. The long sequence of fluvio-lacustrine sediments from the Nihewan Basin preserve a wealth of paleoanthropological remains, which provide opportunity for exploring early human evolution and adaptative behaviors in North China. Previous research has focused on the Yangyuan subbasin, whereas Yuxian subbasin (also one of the main parts of the Nihewan Basin) also developed fluvio-lacustrine sequence and possesses significant scientific value and research potential. Starting from 2015, Professor Pei’s team from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences has led a systematic and continuous Paleolithic archaeological surveys and excavations within the Yuxian subasin. Many archaeological sites and a wealth of stone artifacts and animal fossils were discovered, providing important materials for studying the survival behaviors and environmental adaptations of early humans during Pleistocene in the broader Nihewan Basin.

The Caijiagou site, situated in the Jijiazhuang platform of the northeastern Yuxian subasin, is an important Middle Pleistocene site. It was discovered during field surveys conducted between 2017 and 2018 and comprises three locations: Caijiagou-A, Caijiagou-B, and Caijiagou-C. As the first discovered site, the Caijiagou-A (CJG-A) site was excavated from September to October 2019, exposing an area of about 35 square meters, yielding 349 lithic specimens and 569 animal fossils. Based on the mammalian fauna from the archaeological layer in the arachaeostratigraphic section, the burial age of the site is estimated to be the Middle Pleistocene. Cosmogenic ²⁶Al/¹⁰Be burial dating indicates that early human occupied the site most probably took place between 0.47 ± 0.13 Ma ~ 0.64 ± 0.21 Ma.

Technologically, the CJG-A lithic assemblage consists of 349 artefacts which can be divided into Detatched pieces, Flaked pieces and Pounded pieces. Lithic raw material includes lava show fluvial cortex and suggest sourcing from streams, while siliceous dolomite, chert nodules and quartz derive from the outcrops. Regional geological surveys indicate the raw material were obtained from relatively long distance of about 8 km from the site. Lava is the predominant (77.9%) rock type. Cores, debitage shatter, and retouched tools from CJG-A indicate that freehand percussion was the major knapping technique, while the use of hammer-and-anvil technique is occasionally adopted to knap low-quality dolomite. Although CJG-A reduction sequences are relatively short, resulting in a low degree of flake morphologies and dimensions, high percentage of whole flake type V and VI plus sophisticated flaking modes indicate that relatively high flaking rate and later stages of knapping sequence. Retouched pieces are present in CJG-A lithic assemblage, with proportion of 11.7%. Retouch is normally on flakes or flake fragments even angular shatters. Scraper dominants the tool type, followed by points and denticulates. Retouch is casual in CJG-A assemblages, with no imposition of standardized shapes on blanks. The condition of preservation and trace marks on the animal bones indicate that the accumulation of animal fossils were probably made by early humans.

The CJG-A lithic assemblage is characterized by a core and flake technology which can be assigned to Oldowan-like or Mode 1 technology in East Asia. While, the raw material transportation, persistence using of direct hard hammer percussion, and relatively long sequence of knapping sequence imply the technological diversity and flexibility among the mode 1 technology. This research of CJG-A site bear great significance for the study of human evolution and behavioral adaptations in the Nihewan Basin even North China during the Middle Pleistocene.