U.S. National Archives (Record Group 104 [Denver], Sequence 41, Copies of Letters Sent 1899 - 1905) Público Deposited
National Archives online catalog entry is https://catalog.archives.gov/id/2618835. See also the National Archives & Records Administration numismatic finding aids at https://nnp.wustl.edu/library/archivedetail/538870.
National Archives series description: This series consists of copies of letters sent by the Superintendent of Construction regarding the construction of the U.S. Mint, Denver. The letters include work updates, progress reports, materials lists, and lists of supplies to be ordered.