The stress field in the Earth’s crust, often represented as the orientation of the maximum horizontal compressive stress (SHmax), is an important parameter for a wide variety of investigations in solid-earth geophysics. The orientations and magnitudes of the principal stresses determine faulting types and the orientation of new fractures, are related to anisotropy in elasticity and permeability, and can affect wave propagation. Our understanding of the stress field in the Earth’s crust is built mostly upon earthquake source characteristics, borehole-based measurements, and modeling. Observations are sparse and unevenly distributed, and the level of heterogeneity is not well known. Compliant features in rocks, such as grain boundaries and small fractures are very sensitive to the stress field and changes in the stress field. Due to an asymmetry in the way that rocks relax during extension and compression, we observe stress-induced anisotropy in the behavior of compliant features in rocks due to the horizontally anisotropic stress field in the Earth. Thus, we can infer the orientation of the horizontal principal stresses using differential travel time measurements of differential Green Functions taken at different azimuths. We applied this method to Rock Valley at the Nevada National Security Site for building geophysical models associated with discriminating underground explosions from earthquakes.