Data Originally Given In Long Tons Were Converted To Short Tons By NBER. Source: U.S. Geological Survey, Mineral Resources (Checked With D. Houston And Company, Copper Manual, 1904, Vol. Iii, Pp. 82-85).
This NBER data series m01138 appears on the NBER website in Chapter 1 at http://www.nber.org/databases/macrohistory/contents/chapter01.html.
NBER Indicator: m01138
Release: NBER Macrohistory Database
National Bureau of Economic Research, Copper Production for United States [M01138USM601NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M01138USM601NNBR/, August 31, 2015.