This primary source comes from the Records of the Office of the Chief Signal Officer.
National Archives Identifier:
531057Full Citation: San Francisco Earthquake of 1906: United States Signal Corps telegraph office; ca. 1906; Records of the Office of the Chief Signal Officer, Record Group 111. [Online Version, https://www.docsteach.org/documents/document/san-francisco-earthquake-of-1906-united-states-signal-corps-telegraph-office, May 11, 2024]