Emerald Cove
From Halopedia, the Halo wiki
Emerald Cove was a UNSC colony world. During their training, the Spartans were sent on an underwater mission with Chief Petty Officer Mendez. Mendez sabotaged half of the Spartan's air tanks, so they stole his. They then ditched him and camped out on an island for a week, with nothing to do but light bonfires, bake clams and surf. It was a good memory they enjoyed sharing.
In 2542, the UNSC abandoned Emerald Cove due to the danger from the Covenant. The Covenant most likely glassed the world afterwards.