Several people in Mayberry, North Carolina, had exact look-alikes who could be found in other locations, other TV shows.
Andy Taylor had an identical cousin named Andy Sawyer, who was mayor of Greenwood, North Carolina. They were named after the grandfather they shared. ('The New Andy Griffith Show')
Floyd Lawson had a half-brother named Mitchell Lawson (although we only know him addressed as Mitchell.) As seen in "Hocus Pocus And Frisby", an episode of 'The Twilight Zone'.....
Besides her sister Nora, Aunt Bee Taylor had an identical half-sister in Mayberry named Henrietta Perkins. That one of their fathers had fooled around with the other's mother was a scandal which the good people of Mayberry never spoke about... in public. ('The Danny Thomas Show' - "Danny Meets Andy Griffith")
But Goober Pyle was the only citizen of Mayberry to have an evil twin.....
Pierce was the deputy sheriff in a small town further west and south of Mayberry. He was a racist and had hatred in his heart for his fellow man in all walks of life. In fact, it may have been the overwhelming bile in his soul that contributed the most when there was a severe atmospheric change above the town in 1964 - on the morning of a prisoner's execution, the sun never "came up". The sky over the town remained dark as pitch.
The anger and hate in the hearts and souls of the townsfolk contributed and may have caused the "event". At least that's the way Reverend Anderson saw it:
"In all this darkness, is there anybody who can make out the truth? He hated, and he killed, and now he died. And you hate, and you kill. And now there's not one of you, not one of you, who isn't doomed. Do you know why it's dark? Do you know why it's night all around us? Do you know what the blackness is? It's the hate he felt. The hate you felt. The hate all of us feel. And it's too much of it, it's just too much. And so we had to vomit it up, and now it's coming up all around us and choking us. So much hate, so much misery and hate."
As far as I can imagine, the situation remains that way to this day. The government probably cordoned off the town; perhaps not even letting those people to leave, due to fears of contamination of the skies over the rest of the country. (As the episode ended, the townsfolk learned that it was happening in Dallas and all over the world.)
The town has been forgotten by the general populace of "Telemerica". It's now probably just a an entry in some misplaced dusty old folder in 'The X-Files'.....