Like the Alpha Site, the Gamma Site is an off-world base established by the SGC. The planet, 24,000 light years from Earth, was chosen for several reasons, including its unique radioactive ionosphere which makes it difficult to lock on to surface targets from orbit, thus reducing the chance that the stargate could be stolen. An above-ground bunker was built in a clearing on the forested world, with a communications tower and a hangar and runway for F-302 craft, but much of the facility was constructed below ground in a structure similar in appearance to the SGC. The facility was largely used for scientific research, and over 30 scientists were engaged in ongoing projects, including Dr. Myers, the lead entomologist, his partner, Dr. Pullman, Dr. Sharma, the lead botanist, Dr. Toshiaki, conducting a magnetic resonance field study, and Dr. Santiago, studying mealworms. An unmanned research station had also been built on the planet approximately 10 kilometers from the main facility.
In an effort to improve public relations between the International Oversight Advisory and the SGC, the Pentagon made arrangements for four members of the IOA, including Chapman, La Pierre, Shen Xiaoyi, and Richard Woolsey, to make their first off-world visit through the stargate to tour the Gamma Site facility. Although access to the more sensitive areas was restricted, the visitors were introduced to the various research projects on the base, including Dr. Meyers's study of R75, an alien carnivorous insect specimen that reproduced at an extreme rate. During the visit, however, the R75 insects breached containment and swarmed the gateroom, making escape impossible. Colonel Pearson, the commander of the facility, ordered that the base be put under lockdown, and SG-1 was escorted to the surface before the autodestruct command was triggered. The Gamma Site facility was destroyed and left in smoking ruins.
Under the assumption that the base had been lost, the SGC enacted Protocol CR91, in which the Odyssey would launch a payload of neurotoxin lethal to both R75 and to humans, allowing the SGC to later mount a salvage operation. SG-1, however, led the IOA delegates through the forest and rocky terrain to the research station, with the swarming subterranean insects in close pursuit. There they were able to amplify their communication signal enough to be picked up through the radioactive ionosphere, and Odyssey beamed them aboard before the neurotoxin was deployed.
Although the Gamma Site facility was destroyed, a Gamma Site was later rebuilt. When SG-1 attempted to establish a wormhole between the supergate and a black hole in the Pegasus Galaxy, Atlantis was able to contact the Odyssey by relaying their message through the stargate to the SGC, then to the Gamma Site where the SG-11 Comm Officer forwarded the radio message via subspace relay to Teal'c near the supergate, who then transmitted the message through the active stargate to Odyssey.
Episode Reference: The Scourge