Mining silver continued as an enterprise, but copper emerged as a valuable mining resource as electricity became an important technological innovation. The creation of telephone and telegraph networks meant large-scale demand for copper wiring. Individual foreign entrepreneurs and companies purchased mining sites. Among the owners were Amalgamated Copper Company, American Telephone and Telegraph, American Smelting and Refining Company, and Phelps Dodge. The Greene Consolidated Copper Company became infamous in Mexico when its Cananea mine workers went on strike in 1906 and the rurales in Mexico and Arizona Rangers suppressed it.