Geological Survey Professional Paper 387—B Recent Activity of Glaciers of Mount Rainier, Washington

Puyallup Glacier (figs. 1 and 2 on pl. 4) came to within 250 yards of the present parking area at the end of West Side Road about 120 years ago. During the advance to this point, ice cascaded in tongues down two steep valleys (fig. 3 on pl. 4) and joined, to flow downvalley. The moraines that were left when the glacier receded are low and quite short. Two active rock slides eroded or buried lateral moraines on the steep valley wall north of the Puyallup River. These slides and snow avalanches or a wind storm, or both, destroyed a large area of forest that recently grew on the moraines. A few trees remain on two prominent ridges in the valley bottom on the north side of the river (map on pl. 4).

The 19 trees sampled in four areas (table 5) include most of the large trees on two moraines of Puyallup Glacier. This small number of trees did not permit us to select trees of many different species or of a wide range of trunk diameters. It is not possible, then, to conclude that the oldest sampled trees are among the first to grow after the ice receded. The oldest in areas 1 and 3 indicate that the moraine represents the position from which the northern tongue of Puyallup Glacier started to recede about 1840. Another more conspicuous moraine (area 4, map on pl. 4), visible from the parking area at the end of the closed part of West Side Road (fig. 3 on pl 4), is characterized by many fallen tree trunks, alder shrubs, and a few standing trees. This ridge is upvalley from the 1840 moraine.

These two ridges represent the maximum down valley position of Puyallup Glacier in modern time. Tree ages show that the glacier was not farther downvalley after 1846 than the position of the moraines discussed above (map and fig. 3 on pl. 4).

TABLE 5.—Puyallup Glacier: ages of trees sampled from periglacial features

[Periglacial features : moraines]