OK, guys, you've forced me to go check my sources. When will I learn that it doesn't pay to "shoot from the lip" on this board. What I should have said was:
Capt. Clark records that Charbonneau was discharged and paid off on August 17. This interpreter, husband of Sacajawea, “was offered conveyance to the head of the Illinois if he chose to go. He declined . . . observing that he had no acquaintance or prospects of making a liveing below, and must continue to live in the way he had done.” So, Charbonneau and his “blacksmith shop” remained with the Mandans, thus establishing the earliest known “permanent” smithy on the upper Missouri.
Firearms, Traps and Tools of the Mountain Men , Carl P Russell, The University of New Mexico Press, ISBN 0-8263-0465-6
So it wasn't the first shop west of the Missouri as I said.