Borderlands 2 Highlands Outwash is a transitional area that is much smaller than The Highlands, and it can be accessed the same time as The Highlands region. It also lacks the presence of NPCs or bounty boards.
SPOILERS AHEAD!
Borderlands 2 Highlands Outwash is connected to The Fridge area through an exit point on the eastern side of the map, and on the western side it has two exit points to The Highlands area.
Half of this region is similar in aspect with The Highlands area (rocks and mountains with grass and waterfalls), and the other half is occupied by a large facility, known as Hyperion Extraction Plant, which is probably the most important location we can find here.
Because of the regions size, the vending machines can be found in one place only, next to the Fast Travel system. Also, the Catch-a-Ride system is missing.
Inside the Hyperion installation we can find the usual enemies, the robot loaders and the human engineers, whereas other zones are populated with stalkers, which are incredibly fast creatures that can cloak when their shield isnt depleted. The threshers, however, are much rarer than in The Highlands area, with the sole exception of some missions, listed in the following Borderlands 2 walkthrough.
List of Missions
Optional Missions
Slap-Happy Mission Walkthrough
Borderlands 2 The Highlands Outwash Map