I'm trying to find if there is some geological connection between the rivers, e.g. A, B, and C are part of the same "watershed" or maybe same "river valley", "river system" or something, but these terms don't seem to fit my searches. The term "river valley" seems closest, but I can't find people using this term in the same context, and also the rivers are 100-200 miles long, hardly seems a valley can be that big. These are rivers flowing into "dips" that are easily 100 miles wide.
Is there any common term and way a geologist will find a connection between several rivers sharing a specific area?
Sure, other factors come into play, like distance, weather, and food availability, but mountains, aka "orographic barriers" require significant material and energy resources to overcome. Even low hills present a challenge to a calorie-scarce community. An "orographic barrier" is an "energy barrier" in many different ways.