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.