This is literally the same river as in my previous diagram, but now made to look like an actual river. It’s composed of maps of actual rivers at different scales, some rotated or mirrored. Green dots are cities, orange dots are trade posts.
Once I overlayed a hex grid in GIMP and set it to correspond to 100 miles for the river delta, I was able to count the actual distances, and it turned out that just by eyeballing, I got amazingly close to the numbers I had drawn up with no references yesterday. The Black River and Western Green River are 200 miles shorter than I had planned, but the length of Eastern Green River and the junctions of the main branches are all only 10 miles off from what I wanted. For reference, the Black River and the Lower River are based on the Mississippi at half-length, so it’s still a really big river.
I’m not quite happy with many of the side branches and will probably bend the Black River more south to make room for a big mountain range between it and the Green River, and maybe turn the Western Green River more southwest, but other than that I am really happy with this for a first attempt.