Your shotgun, unlike the fake guns marked Wells Fargo is worth quite a lot. The last 2 auctions that I found with "Pine Ridge Indian Agency" were from 2014. One sold for $1900 and the other sold for $2050.
Your gun should have a value of $2000 to $2200.
Henri Pieper made and designed many different guns. The following link will take you to information about him and some of the guns he produced.