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ABSTRACT Constructing underground tunnels and associated infrastructure in tectonically sensitive mountainous regions such as Bilaspur, Himachal Pradesh, presents significant engineering challenges due to variable rock mass properties, complex deformational behavior and weak litho‐structural conditions. Detailed pre‐investigation of geological and structural characteristics is therefore essential to evaluate rock stability prior to infrastructure development, particularly in steep terrains that exhibit elevated geotechnical and environmental risks. This study assesses rock mass quality using the rock mass rating (RMR) geomechanical classification system based on detailed field investigations, including intact rock strength, rock quality designation (RQD), discontinuity spacing, discontinuity condition, groundwater condition, and discontinuity orientation. To enhance the reliability of stability assessment, geographic information system (GIS)‐based spatial analysis was integrated to evaluate terrain slope, fault distribution, lineaments and regional seismicity. Although GIS parameters were not used directly in RMR computation, they were employed as an independent spatial validation framework to examine the consistency between geomechanical classification and regional structural controls. The results indicate RMR values ranging from 21 to 30, corresponding to Class IV (poor rock mass quality), primarily controlled by closely spaced discontinuities and unfavorable structural orientations. The novelty of this study lies in integrating field‐based geomechanical classification with GIS‐derived tectonic and geomorphological analyses to provide spatial validation of tunnel stability conditions in a tectonically sensitive Himalayan terrain, enabling improved assessment of engineering feasibility beyond conventional RMR evaluation. The findings suggest that tunnel construction in the study area requires enhanced support systems, including the New Austrian Tunneling Method (NATM), rock bolting, steel ribs, and shotcrete to ensure long‐term stability. This integrated framework provides a practical basis for planning railway tunnel infrastructure in structurally complex mountain environments.