Mark Twain! All I hear about is that old fart, Mark Twain! Well, I was steaming the Mighty Mississippi when he was but a gleam in his Granddaddy's eye!
Antique Maps XXXII - Mississippi River Basin of the 1700s details the Louisiana Territory, and the course of the Mississippi River, as it was charted in the 1700s. This map is very detailed. The image file is at 300dpi, with the printed map being 11 inches high, by 11 inches wide.