Chile, 2,600 miles long and 100 miles wide, extends from the arid deserts of the North to the cold, windy pampas of the South. It occupies the area from the crest of the Andes to the Pacific Ocean. Geologically, it occupies a long, mobile belt lying west of the stable shield area. Through a series of orogenies it has developed the present Cordilleras. This Andean geosyncline has been a zone of weakness from Precambrian time to the present.

The Andean Cordillera, one of the highest mountain chains in the world, is complicated geologically and tectonically. Two principal provinces can be described, the Eastern and Western, separated by the great central valley of Chile, in which lies the capital, Santiago. The Western Cordillera, the older, represents an extensive batholith of continental character, and is largely granitic in character. Normal block faulting and folding occur. The principal uplift occurred in the Upper Mesozoic. The Eastern Cordillera is composed principally of metamorphic and sedimentary rocks, although evidences of its crystalline core are common. Structurally they show block faulting, with some evidence of thrusting toward the east. Principal uplift occurred during the Tertiary and Quaternary.

Close inshore in the Pacific are troughs 23,000 feet deep. Recent vulcanism is common. At the southern end of Chile the Andes make a strong eastward swing and thence, by an island arc very similar to the Caribbean Island Arc, join the Andes to the mountains of the Palmer Peninsula of the Antarctic, 600 miles south.

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