Archival methods
Aerial spy photography collected by the United States in January 1945 covered part of the research area between modern-day San Vicente (Campo Cuatro) and Sagrada (Campo Seis). After gaining access to these photos from NARA, we created an orthomosaic of the overlapping images and georeferenced it to generate topographic data and trace visible sections of the rail line (Supplemental Figure 12).
In 1932 and 1933, a 24-year-old logging engineer Charles Tebbe identified inefficiencies at the Camp Isarog mill and set up a new mill site in Tandoc; while there he took many photos (see Figures 3–5; Supplemental Figures 1–10).
His travelogue and photos were bound into a single copy of a book, "Butuanan," held at UC Berkeley's Bancroft library.