The wall itself was created by Little Pete on the day the FAYZ happened. When the Gaiaphage caused the meltdown at the power plant Pete created the wall which contained people under the age of 15 inside. It later came to be known as the FAYZ Wall. It is a clear dome 20 miles north, south, east and west of the PBN Spoiler alert!!
In Gone, the wall is discovered first by Edilio, who tries to dig his way down but discovers that it continues downwards as well. They also discover that it is painful at the touch. Later Lana is shown to discover the barrier after she manages to heal herself from her wounds caused by the crash of her grandfather's truck.
In Lies Orsay Pettijohn claims to be able to see beyond the FAYZ wall see the dreams and people who have "escaped" the FAYZ. In the end of the book when Mary Terrafino commits suicide by jumping off the cliff with the littles and Dekka and Brianna save the littles Little Pete's gameboy is broken and he takes down the wall for a few seconds. However it is unknown if this was an illusion of the Gaiaphage or of it was real.
In Fear, the first mention of the wall was back in the mineshaft where Drake/Brittney have been staying with the Gaiaphage for the last four months. Drake then notices a black stain starting to form from the Gaiaphage which later spread onto the wall. The next appearance of the wall is when Sinder and Jezzie notice it up at Lake Tramonto while farming and rush to show it to Sam. Astrid also notices it and a few streaks of dirt stuck onto the wall something which has previously not occured. Astrid later goes back to the Lake and tries to calculate the speed of the stain which grows. Quinn notices the stain while fishing. Later on the barrier goes entirley black and people build fires, panic and set things on fire. However at the end of the book, after a nuclear bomb is detonated at the barrier, it turns transparent which allows communication with the outside world.
In Light, the wall is transparent. Near the end of the book both little Pete and the Gaiaphage die; at the same time the wall collapses. It is Little Pete's death that destroyed the barrier.The Gaiaphage's death got rid of the mutant powers