The New International Encyclopædia…
“ Mining. Arizona probably contains a larger proportion of ore and mineral-bearing land than any other member of the Union, but the lack of transportation facilities has prevented a normal development of the mining industry. In spite of this difficulty, however, mining has been undergoing a steady growth, and constitutes the most important industry of the Territory. Copper mining, in which Arizona ranks next to Michigan and Montana, is the most important. The Territory produces more than one-fifth of the total output of the United States. ”
