Yuma County was one of the earliest important mineral·producing areas in Arizona . Numerous large and small mining and placer operations were active, and almost all the more important mineral deposits of precious and base metals in the county were first found and prospected during the second half of the 19th century . The records of most of those early mining activities are scanty and scattered in old documents and records, publications by individuals or Federal and State agencies , articles in technical journals, public and private reports , and newspaper clippings. Even si nce 1900, the mining records are far from complete and are not readily available to persons needing or seeking such information. Thus this index is designed to provide, in a concise form, a summary of the available information on most of the mining properties in the county and the more important sources of information that may be found concerning those properties.