The role of the U.S. Army Corps of Engineers in opening the West is not as well known as the Corps' work on nationwide flood control and navigation projects. Yet, in the 19th century the surveys, explorations, scientific studies, and reports of Army engineer and topographical officers were major contributions to our understanding of the undeveloped arid regions of the United States. The following report illustrates the skill and dedication of these soldiers. The Board of Commissioners that explored the interior valleys of California was composed of two Army engineer officers and one civilian scientist for the Coast Survey. Their report, published in 1874, was the first federal irrigation survey. It still has value for its detailed information on central California and on irrigation practice in the American West and, indeed, around the world. The introductory essay puts the report into its historical setting and provides a wealth of information about both the survey and the political and economic forces that dominated California over a hundred years ago. I trust the report and the essay will be of interest to all those interested in the development of the West. Robert W. Page Assistant Secretary of the Army (Civil Works)