How did early explorers determine the source of a river? did they simply follow a river or a different way?

Answer 1

The followed the river upstream trying to keep to the larges stream when they came to a fork.

If you have ever read any history you might recall that Lewis and Clark had trouble deciding which was the Missouri river and which was a tributary as they approached the headwaters.

I also suspect that they did some guessing. having crossed a stream once and then cross another to the east or west or north or south of the original crossing might suspect that it was the same stream. Maybe that is why we have 2 Canadian rivers, 2 Platte rivers, 2 Red rivers, 2 Blue rivers etc.

Answer 2

I suppose they start their exploration from the source or are already aware of the source, but I'm not Loius and Clark, or John Wesley Powell, do you think Pocohontis was hot?

Answer 3

looked at their map