Minda is worried about an Oseram girl who fled west out into the desert. Being afraid to go, Minda wants you to handle it and bring the girl back safely. It’s time to brave the sands of the Forbidden West and go on a rescue mission. Here is how you complete the Signal Spike side quest in Horizon Forbidden West.
You won’t be able to retrieve this quest until you have completed the Eye of the Earth story mission and unlocked the Base. Once that is complete, go southwest of the Base to the settlement called Camp Nowhere. This small camp is where you will find Minda and retrieve the quest.
Follow the marker west until you reach the area where Silga is. You will know when you reach the right area because you will hear Silga shouting and see multiple machines. Kill the machines. Once they are all destroyed, talk to Silga. Silga is trying to get her radio operational and you are going to need to help.
You will now need to follow the wire up the mountain. From the first spike next to where Silga is, follow the attached wire. It will go from spike to spike until it stops at the top of the mountain. Press the triangle button to interact with the radio tower on the mountaintop. This will pull up your Focus. Move the cursor around until you get more of the radio message. Head back down the mountain and talk to Silga.
You are now going to need to head to two other areas. For starters, head up north past the Tallneck in The Shining Wastes. You are looking for the settlement known as Scalding Spear. When you reach the area, you will need to climb up the massive tower in the settlement. The tower is easy to climb and has obvious handholds.
After going to Scalding Spear, you can use the campfire to fast travel to your Base. This will allow you to climb the mountain above the Base relatively quickly. You will need to fight a few machines along the way. Once you reach the top and scan the area, go to the next waypoint. You can easily get there by gliding from the top of the mountain.
When you arrive at the area where the signal is coming from, you will need to clear the area of machines. After you defeat the machines, use your Focus to find the source of the signal. You’ll find the source behind a wall of rubble and through an underwater section. Once you uncover the cache, return to Silga for your reward.