The ice sheet covered all of Chile south of Puerto Montt plus the western fringes of Argentine Patagonia.

The ice sheet extended beyond the crest of the Andes into Argentina, but because of the dryness of the climate it did not reach beyond present-day lakes such as the Yagagtoo, Musters, and Colhue Huapi.

With each successive glaciation it is known that the ice has stopped further and further to the west, with aridity always serving as the decisive factor halting glacier spread: it is believed that the east-west precipitation gradients during glacial periods were even steeper than the extremely steep ones of present-day Patagonia.

This is because the flora remaining to the north of the ice were isolated by the Atacama Desert and were able to speciate easily wherever suitable microclimates occurred.

However, there are indications that during the last deglaciation (17,500 years ago), the rapid melting of the northernmost extension of the Patagonian Ice Sheet resulted in a dramatic release of freshwater to the adjacent ocean, decreasing its salinity[3] and altering its circulation, resulting in significant ecological changes both locally and remotely.