(recently created), and Quang Ngai Provinces. All are coastal provinces and, with the exception of Quang Ngai, extend inland from the seacoast to the Laotian border, a distance which varies between 30 and 70 miles. Together, they occupy the central portion of the region formerly known as Annam and extend 225 miles to the south of the DMZ.
The climatic pattern in the northern provinces is the exact reverse of that which affects the southern portion of the nation. In I Corps the dry season occurs in the summer months while the monsoons, which blow from the northeast, dominate the winter. Heavy monsoon rains accompanied by wind and fog normally begin in October. After reaching their peak usually in November, the monsoon rains tend to diminish gradually until their disappearance around mid-March.
The differences between the physical structure of the northern provinces and the Mekong Delta is even more striking than their reversed climatic patterns. White beaches stretch almost unbroken along the entire length of I Corps. Just inland and roughly parallel to the coast south of Da Nang lies a lightly populated strip of sand dunes and generally unproductive soil. This strip varies in width from one half to two miles. In the west it dissolves into the flat, densely populated coastal plain. Any similarity between the Mekong Delta and the northern provinces is found in this expanse of fertile rice-producing land where tiny rural hamlets and slightly larger villages, each enclosed by thick hedgerows and treelines, abound. North of Da Nang the semi-barren coastal sands tend to extend farther inland, and thereby reduce the productive portion of the coastal plains.
The most distinct geographic feature of I Corps, and one easily visible to the Marines at Da Nang, is the chain of towering mountains which protrude from the flat coastal plain several miles west of the city. There is a conspicuous absence of foothills leading to the mountains which seem to surround Da Nang on the north and west. North of the Hai Van Peninsula, a rugged promonotory which juts into the South China Sea about 10 miles north of the Marines' new home, a zone of foothills eases the transition from the wide coastal plain to the rugged jungle-covered mountains.
The coastal plains of the five northern provinces are broken by several significant streams along which most of the region's principal population centers are located. Roughly 10 miles south of the 1954 partition line the Cua Viet empties into the southern portion of the Tonkin Gulf. Both Quang Tri City, the capital of Quang Tri Province, and Dong Ha, South Vietnam's northernmost population center of any significance, are situated on the Cua Viet and its major tributary, the Song Cam Lo. The Song Huong (often referred to as the Perfume River), which flows past the old imperial capital of Hue, enters the sea at a point approximately half way between Da Nang and the nation's northern boundary.* At Da Nang the Song Han (also called the Da Nang River) flows into Da Nang Harbor after its main tributary, the Song Cau Do, curves through the coastal plains immediately south and west of the city. Eighteen miles south of the Marines' new base of operations, the Song Cau Dai empties into the South China Sea near Hoi An, the capital of Quang Nam Province. The Song Cau Dai originates about 18 miles inland at the confluence of the Song Thu Bon and the Song Vu Gia which twist seaward from the south and west respectively. Together these three estuaries constitute the most important geographic feature of the sprawling coastal plain south of Da Nang. Another major stream, the Song Tra Bong, flows on an eastward course about 32 miles south of the Song Cau Dai. Still further south is the Song Tra Khuc, a river which dominates the wide coastal plain of Quang Ngai Province in much the same fashion as does the Song Cau Dai and its tributaries in the area south of Da Nang. The provincial capital, Quang Ngai, once a major railroad center for South Vietnam, is situated several miles inland on the south bank of the Song Tra Khuc. The southernmost stream of any significance in I Corps is the Song Ve, which angles northeastward through central Quang Ngai Province. While none of these waterways is navigable far beyond its mouth by ocean-going vessels, each serves the local population as convenient local routes of communication as well as vital sources of irrigation water during the long dry seasons.
The two and a half million people who inhabited I Corps in 1962 had developed along social and economic lines dictated largely by the geography and climate of their region. Rice growing, centered
*In the Vietnamese language the word "song" means stream and normally precedes the name of rivers.
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