This is a handmade map from the construction of the Panama Canal, one of history’s greatest feats of engineering. Culebra Cut is where the project experienced massive landslides (is it fair to say some of them are still going on today? I think it is… it is).
So the folks in charge of the dig, the Isthmian Canal Commission, got geologists down there to study how to move all that dirt out of the way without burying any workers and steam shovels and train cars.
This is one section of the dirt-profile from AB Nichols’ notebooks. It’s labeled “Isthmian Canal Commission. Partial Geological Profile along axis of Canal in Culebra Cut, by A.B. Nichols and A. Raggi. 1910.” I found it in the Linda Hall Library Digital Collection.