This book deals with the rapid erosion of deep stream gullies (arroyos) which have become a feature of many valleys of America's South-western states since the middle of the 19th century. The nature and causes of entrenchment have been a matter of interest and practical concern to research workers in the environmental sciences and some fields of terrain management for many years, but the abundant records of environmental change in California and Arizona relevant to the study of historical arroyos have never before been systematically collated and analysed. Those concerned with environmental change or with an interest in fragile, semi-arid environments.