Final answer:
The common climate type on the west coast of South America, west of the Andes Mountains, is a desert climate (Type B), evidenced by the arid Atacama Desert.
Step-by-step explanation:
The most common climate type on the west coast of South America, to the west of the Andes Mountains, is characterized as a desert climate, which is a Type B climate. This is exemplified by the Atacama Desert, which is one of the driest places on earth. The lack of precipitation in this region is primarily due to the rain shadow effect caused by the Andes Mountains, which blocks moisture and creates a very arid environment.