The Flow Of Information Was A Little Slower

From Lewis and Clark National Historic Trail:

For those of us who have read the journals of Lewis and Clark or the others, we know that nearly every stream or river west of Fort Mandan was named by the Captains. Yet today, few of their names appear on current maps. Why is that?

It’s probably due to the fact of how long it took for the journals to be published and distributed. Trappers and miners who came after the Expedition in the early 19th century also gave the rivers names, not realizing that Lewis and Clark had already named them. 

For example, today’s Monture Creek in Montana was originally named Seaman’s Creek after Lewis’s pet dog.