Describes a monitoring system installed at the Anasazi ruins of Mesa Verde National Park, Colorado. Two test walls were constructed of sandstone masonry blocks, and electronic temperature and moisture sensors have been embedded in the blocks without disturbing any actual intact cliff dwelling ruins. At regular intervals, photomicrographs are made of reference areas on each block in the test walls. Successive photomicrographs are compared and the removal of individual grains of the sandstone is thus observed. From the grain-loss counts, it is possible to determine even very small average erosion rates for the surface, because the Mesa Verde sandstones have very uniform grain sizes. Microclimate and air quality data are collected on site. Electron microscopy and other microanalysis methods are used to observe minute changes in the chemical, mineralogical, and physical makeup of the sandstone as it is exposed to the environment. The ultimate objective is to determine whether airborne acidic pollutants can accelerate the alteration of the cementing phases by natural weathering processes, thereby hastening the deterioration of the masonry walls.