Western Ghats (WG) in India is endowed with one of the most distinctive and picturesque mountainous landscapes. The region encounters unprecedented rain and non-engineered excavations (especially along highway cut slopes), that turns out to be detrimental to the stability of rock and soil slopes. The present research focuses on accounting the vulnerability condition of rock slopes of differential deterioration intensities along National Highway corridor 66 (NH 66) at Ratnagiri–Sangameshwar (RS) stretch. Rock mass and associated slope stability condition were encapsulated, and studied locations were classified using different geo-engineering classification (GEC) systems such as RMR (Rock Mass Rating), SMR(Slope Mass Rating), CSMR (Continuous Slope Mass Rating), GSI (Geological Strength Index) and RDA (Rock slope Deterioration Assessment). The study introduces a new class in RDA for igneous rocks that are susceptible to high deterioration. Some useful insights have been added and discussed in the light of deterioration-induced block failures which have been integrated with detailed kinematic analysis. The present study recommends that RDA would prove more efficient and informative in the preliminary stage of slope stability investigation for high deterioration susceptible igneous rock masses as compared to other geo-engineering systems.