ABSTRACT: Hydraulic stimulation and production-induced permeability alteration in stress-sensitive Monterey Formation rocks require an in-depth understanding of the deformation behavior of different rock types. Here, we evaluate and compare deformation behavior of two types of clastic rocks—shale and sandstone—across nano-to-micro scales using experiments and simulations. Using core samples of shale from the Monterey Formation and tight sandstone from the Dominguez Hills in California, we conduct nanoindentation, scanning electron microscopy and particle-based simulation to understand the difference in deformation behavior of shale and sandstone under different loading-unloading conditions. We quantify Young’s modulus, hardness modulus, and stiffness of the rocks using nanoindentation data. Our work provides important insights into grain-scale deformation behavior of two different rock types commonly found in petroleum reservoirs. Understanding of grain-scale failure mechanisms can inform development of new upscaled constitutive models for usage in continuum-scale field simulations, which cannot afford to resolve the grain-scale processes due to computational cost.