The West Virginia Base was a Mogadorian base inside of a mountain in West Virginia. It is also called the Hawks Nest. Six, Nine, Sandor, and Sam Goode were prisoners here. In The Power of Six, John and Sam snuck into this base to retrieve John's chest.
Six was captive here around the age of 13/14. She was captured in New York. Her Cepan, Katarina, was killed in captivity. Six developed invisibility and killed Katarina's murderer before escaping.
Nine was held captive here around the age of 16/17. He was captured sometime after Three's death after falling for a human operative of the Mogadorians, Maddy. In captivity, he watched Maddy and her parents get eaten by a Piken.
At a point in his captivity, Sandor was being tortured in front of him and Nine managed to break through the forcefield. He killed Sandor to end his suffering. In his cell, Nine dedicated himself to training. He is set free by John and Sam when they sneak into the base.