Jeju uprising to Jeju from Busan and deploying police companies, each 1,700 strong, from the southern provinces of the mainland. The guerrillas retreated to their bases in the forests and caves around Hallasan, an extinct volcano and the highest mountain in South Korea. On April 29, the Korean, non-military, governor of Jeju province abandoned his post, defected, and joined the guerrillas. This caused many police officers, disillusioned by the atrocities they were ordered to commit against their own, to do the same. In response, U.S. military provincial governor William F. Dean ordered a purge of SKLP sympathizers from the ranks of the
Hallasan than in other areas, and the lowest temperature often appears at night. When the weak northwestern synoptic winds are blown, the lowest temperature appears in the eastern part of Jeju Island. The chill of the top of Hallasan descends downhill along the mountain range and is collected in the eastern part of Jeju Island so the morning temperature drops a lot. For the last five years, the deviation of temperature (maximum temperature - minimum temperature) increased in spring between March and May. The reason for the large deviation in spring is because the phenomenon occurs frequently by Hallasan. Hallasan was