Rock riprap erosion protection is normally used at radioactive waste disposal sites to stabilize waste covers against wind and water erosion. Federal statutes require that the covers and erosion protection remain effective for hundreds of years, without placing reliance on active maintenance. To provide guidance in selecting rock sources to provide this level of protection, the Nuclear Regulatory Commission (NRC) staff developed a quantitative procedure for evaluating the physical characteristics of rock. To refine and improve this procedure, a contract was awarded to Colorado State University (CSU) to gather data on rock types which have survived for long periods of time. Emphasis was placed on obtaining data from marginal-quality sandstone rocks found at petroglyph and rock art sites in the southwestern United States. Rock samples near the petroglyphs were gathered, and standard durability tests were performed on the samples; archaeological information was used to determine the age of the petroglyphs. Even though the information gathered may only be applicable to arid and semi-arid areas, previously-developed NRC testing and scoring procedures will likely be modified and refined as aditional data become available.