A detailed reconnaissance and travel diary documents a survey of a little-known mountain pass through the Andes, offering precise itineraries, measured distances, and careful topographical observations of rivers, valleys, and settlements encountered en route. The author maps alternatives for crossing the Cordillera, proposes making the Rio Claro and connected waterways navigable to link inland towns with the Pacific, and records local geographic and administrative notes on provinces and transit obstacles. Interleaved are technical suggestions, route itineraries, and critiques of neglected infrastructure, all aimed at improving communications and commerce between Buenos Aires and Chile.