Except for several unsuccessful attempts to use modern dredges, there has been little placer mining activity in the State since Bulletin No. 10 was printed. Nevertheless it has been thought wise to rewrite that bulletin completely, at the same time adding many new data. The present bulletin is, in the main, a compilation of information that was already in print, but scattered and difficult to find, and the aim is to present a concise and fairly complete account all the history, production, location, development, and present status of Arizona's placer deposits in a form readily available for the use of all inquirers, and especially those who think they have developed a process that will enable them to work the deposits profitably. There are two main obstacles, more or less peculiar to the state of Arizona, that stand in the way of the successful working of these placers: one, lack of water, is a condition common to practically every district in tbe State; the other, the cementation of the gravel by caliche or lime, is a deterrent in a great number of areas. Many schemes have been devised to overcome these difficulties, but so far none of them has been very successful. These attempts are recounted in the detailed descriptions of the individual placer fields.