Quadra Sigma III was the third planet in the Sigma III planetary system. This planet was the location for a Federation colony with a population of 504, including 38 children.
In 2364 the Sigma III colony transmitted a distress signal for urgent medical help when an explosion resulting from a methane-like gas seeping from underground devastated a mining operation there. The USS Enterprise-D was fortunately close enough to render assistance. (TNG: "Hide and Q")