Severe, occasionally disastrous, erosion of the bases of adobe walls in the arid and semiarid regions of the Southwest is a phenomenon which has long been observed and commented upon. In historic times, erosion of this type has caused collapse of adobe buildings in the Rio Grande Valley of New Mexico; about Tucson, Arizona, it is serious, as it is in the Salt River Valley. Evidence of similar erosion has been noticed in excavations of prehistoric massive adobe or caliche walls of Hohokam and Salado structures of the thirteenth and fourteenth centuries A.D. in the Salt and Gila River valleys of Arizona. Repair to check erosion and prevent collapse of walls was the primary purpose of Cosmos Mindeleff's stay at Casa Grande in the 1890's. Fewkes noticed similar cutting of standing walls at the nearby Adamsville site.