Two architectural conservation projects on the stabilization and treatment of Arizona sandstone have been undertaken taking as case studies the Old Orange County Courthouse (Santa Ana, California) and the Universalist-Unitarian Church in Riverside, California. Both buildings are characterized by climate, architecture, and materials used. Their state of conservation is analyzed; samples of weathered stone were studied petrographically and by scanning electron microscopy/x-ray spectrometry methods and the results are detailed and illustrated. The treatment plan developed involved the setting up of a preliminary set of documentation materials; then cleaning tests were conducted, especially for large areas; the plan presented by the structural engineer for the church called for soil cement grout under the foundation, another grout was used for earthquake resistance; a special injection sleeve was designed to effectively fill crevices. The authors observe that the dramatically different underlying causes of what appeared to be similar deterioration mechanisms may be due to slight climatic differences between two cities. An acknowledgement and a list of materials and suppliers is appended.