The snow and ice that surrounds the small 35-acre crater of Mount Rainier drains to marine water by three different rivers. The northern rim drains to the White, Carbon, and Puyallup Rivers, which all join the main Puyallup stream which enters Puget Sound at Tacoma. Most of the ice and water on the southern side of the peak flows to the Nisqually River, which enters the sound between Tacoma and Olympia. Finally, a small area of the southeastern crater rim marks the head of the Cowlitz River, which flows to the Columbia River at Longview and then the Pacific at Astoria.
The indeterminate spot on Mount Rainier’s crater rim where the Ingraham Glacier begins its journey toward the Cowlitz is notable as the highest elevation in the entire massive Columbia River Basin of over 250,000 square miles, which extends from icefields of the Canadian Rockies to the Tetons of Wyoming. Sadly, this spot is almost diametrically opposite the crater from the highest summit of Rainier, the Columbia Crest.
This spot is also, ironically, about where guided climbs led by RMI up the Disappointment Cleaver route often end. The rationale is often that there is no time to cross the crater to the true summit, and that the view is no better across the rim. But the guides could also mention that this spot is the apex of the largest drainage basin in the northwest.
The spot where the Puyallup and Nisqually basins meet on the crater rim is also indeterminate, but it appears to be close to Columbia Crest. The South Tahoma Glacier has lobes that flow to both river systems, so it is very difficult to draw a watershed line that follows a natural ridge in the area.