Named after Theodore Winthrop, the body of ice covers 3.5 mile2 (9.1 km2) and has a volume of 18.5 billion feet3 (523 million m3).

[2] Starting at over 14,300 feet (4,400 m) at the Columbia Crest, the glacier heads north and descends steeply over the uneven topography of Rainier.

After passing the Prow, the glaciers split up; the Emmons heads east-northeastward and the Winthrop continues northeast.

As the terrain becomes flatter, the Winthrop glacier becomes heavily rock-covered when it terminates in a forest at about 4,900 ft (1,500 m).

Similar flows have stemmed from the Nisqually, Kautz, and South Tahoma glaciers as well.