Umbra was an agro settlement on Caprica near the Thorn forest. It was destroyed in a sneak attack in 7322.
Chameleon was separated from his son Starbuck when the Cylons raided the settlement. This raid was apparently one of the "first raids on Caprica", according to Chameleon, and resulted in nearly three thousand children being orphaned (TOS: "The Man with Nine Lives").