This study was conducted to describe the vegetation of the valley forest in Naesan-ri, Yeoncheon-gun, a border region in northern Gyeonggi Province, and to clarify the relationship between topography and vegetation. From June to October 2022, we surveyed 38 quadrats (20 × 20 m) placed in the valley and on adjacent slopes. The communities were classified with TWINSPAN and tested with MRPP, and their relationship with topographic variables was analyzed using CCA. The vegetation was divided into five communities: a Robinia pseudoacacia community (I), a Robinia pseudoacacia-Cornus controversa community (II), a Carpinus cordata-Acer pictum community (III), a Quercus mongolica community (IV), and a Quercus variabilis- Quercus mongolica community (V) (MRPP; A = 0.376, p < 0.001). Community III, which occurred on the valley talus, was composed of hygrophilous species and was clearly distinguished from the slope and ridge communities by its high species diversity (H′ = 1.4124) and evenness (J′ = 0.8447). CCA indicated that five topographic variables accounted for 25.88% of the total variation in species composition (p = 0.001). Axis 1 positively correlated with elevation, TPI, and slope, capturing the gradient from valley floor to ridge. Individually, elevation and northness significantly influenced species distribution, whereas TWI did not, highlighting the limitations of DEM-based topographic indices in predicting plot-scale micro-moisture conditions.