From Halopedia, the Halo wiki
The Highland Mountains are alpine mountains located in the Viery Territory of the human colony, and UNSC fortress world Reach. Located on Reach's northernmost continent Eposz, the mountains were made of granite and were home to many facilities used by the UNSC.
After the Fall of Reach on August 30, 2552, these mountains were the only area not glassed by the Covenant, though glassing did occur in the area on a small scale. The Covenant concentrated their forces in the region and set up an extensive excavation operation around Menachite Mountain in order to uncover a massive subterranean Forerunner structure.
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