The Northern Patagonian Ice Field, located in southern Chile, is the smaller of two remnant parts in which the Patagonian Ice Sheet in the Andes Mountains of lower South America can be divided. It is completely contained within the boundaries of Laguna San Rafael National Park. The Northern Patagonian Ice Field is a vestige of the Patagonian Ice Sheet, an extensive ice sheet that covered all of Chilean Patagonia and the westernmost parts of Argentine Patagonia during the Quaternary glaciations. Today, with its glaciers largely in retreat and only an area of 4,200 km2 (1,600 sq mi), it is still the second largest continuous mass of ice outside of the polar regions. Survival is based on its elevation (1,100 to 1,500 m (3,600 to 4,900 ft)), favorable terrain and a cool, moist, marine climate. The ice field has 28 exit glaciers, the largest two — San Quintin and San Rafael — nearly reach sea level to the west at the Pacific Ocean. Smaller exit glaciers, like San Valentin and Nef, feed numerous rivers and glacially carved lakes to the east.