Steep and broken terrains of the T'aebaeksanmaek dominate east-central Korea and the Demilitarized Zone (DMZ). These terrains are controlled by geologic elements, prediction of which can be used advantageously by the military commander. Narrow valleys and ridge slopes are controlled variously by trends of fault zones, major joint sets, and metamorphic foliations. The trends of these elements follow predictable patterns and have influenced the evolution of harsh, rugged terrain that complicates mechanized infantry mobility and logistic resupply. Slope-stability problems arise from weathering on both natural slopes and oversteepened road cuts. Of equal significance in terrain analysis of this region are the distributions of intrusive granite bodies and their history of weathering and erosion during the Quaternary. The granite masses commonly weather deeper and are more easily eroded than the quartzose schist and gneiss they intrude. Resistant metamorphic rocks generally form ridgelines and hill crests, whereas granite plutons characteristically form wide, bowl-shaped valleys and depressions. By an unfortunate coincidence of geology and geopolitics, many of these granite-floored features are located just north of the 38th parallel; they provided important staging grounds for the North Korean (NK) invasion of South Korea in June 1950.

Severely contested high points of these terrains were won in a series of costly Allied ground operations during the summer and fall of 1951. The significance of these operations, conducted while negotiations at Panmunjon bogged down, escaped some authors of Korean War history who disagreed about whether the enormous human sacrifice needed to secure the ridges was worthwhile. Terrain analysis of this sector clearly shows that with these victories Allied forces secured the strategic high ground controlling north-south access routes and assured that the final line of demarcation would not follow the original border along the 38th parallel. The Allies seized the staging grounds from which the NK II Corps divisions had launched their invasion of the central and eastern sectors. In “elbowing” the line northward, the Allies also secured the mountainous salient that bounds the 1950 “invasion corridor” on its eastern flank. Arguably, their sacrifice bought long-term peace on the Korean Peninsula. Worthwhile indeed!