An on-going project at the University of Arizona is using Kartchner Caverns in Benson, Arizona as a natural analog to study time-dependent rock failure with subcriticai crack growth modeling. Various material properties of the Escabrosa limestone composing the caverns are required for input into the damage model. Central among these properties are the subcriticai crack growth parameters n and A, which can be calculated from modes I, II, and III fracture toughness tests conducted at different loading rates. This paper presents the results of modes I, II, and III testing on Escabrosa limestone, providing the material properties necessary for the larger goal of modeling breakdown in Kartchner Caverns and applying the model to the long-term stability of rock excavations. Additionally, fracture test results are compared with a previous study by Tae Young Ko at the University of Arizona, which tested Coconino sandstone and determined that the subcriticai crack growth parameters were consistent among modes. This study expands upon Ko's work by adding the characterization of a second rock material in all three modes; preliminary results indicate that for Escabrosa limestone the subcriticai crack growth parameters are not consistent among modes.