Outside of the main entrance to Sunfall, you will see a bunch of refugees and one of them will give you an errand when you talk to him. His sister, Shianah, is ill and the only healer in Sunfall will likely not even bother with trying to cure her, so Aloy decides to have a talk with him to see if she can persuade him. From the campfire right outside of Sunfall, follow the road to the south, ignoring all forks and continuing straight south.
Eventually, you will come to a three-way split, with one way going straight south, another heading southeast and the last going north. The northern path will lead you to Blazon Arch, a settlement where you’ll find Ghaliv. Speak with him and he asks for a Thunderjaw Heart in exchange for his services, talking about one at the Valley of Omens. Take the path back to the three-way split, returning north to the first split as if you were returning to Sunfall. Instead of continuing north, go west and follow this path until you reach the entrance to the valley.
The Thunderjaw is the only enemy in the valley and can be found to the north. There is a Metal Flower in this valley, as well as a Datapoint, but focus on the task at hand, as the Thunderjaw is a formidable opponent. You can find a full breakdown of the machine on its respective page, but the basic strategy to downing one of these things is to knock off the Disc Launchers first and foremost, as they are powerful weapons that can be used against them.
During this hail of fire, you should probably have knocked off the plating covering the heart, which receives major damage. The Ropecaster (Shadow version is best) is great for tying down the Thunderjaw and allowing yourself a free hit on a weak spot. The Valley of Omens is not an ideal spot for fighting the Thunderjaw, so you may need to lure it a bit north to have more space. Once you down the large beast, loot the Heart and double back to the tent camp at Sunfall. Speak with Ghaliv to hand him the Heart, then talk with Abas to finish up the quest.
|For helping heal his sister||5,500 XP|