From here before we get on with the story quest we're going to be finishing off the Crew Challenges. We will be coming back to Floodmoor Basin a couple more times, but each of those are pretty much just to pick up quests before heading to other areas. Head to 20 to grab the last Typhon Log. From here go left along the wall until you find an alcove with a Keep Out sign. Head into here to discover the location of Jason's Waterfall. Thank me later, because I spent about an hour running around the area in the end game looking for that one location I hadn't discovered, and it was this tiny nook!
Go to 21 to do the Legendary Hunt. At the back of this area is the last of the red chests. Next head to 22 which is where the Deaddrop is, and finally to 23 which is the transition to the next area.
20-23 are not on the map for this area.