The next volcanic eruptions, which may have begun between 25 and 30 million years ago, differed from those of Ohanapecosh time. These volcanoes, somewhere beyond the boundaries of the park, erupted great flows of hot pumice that, being highly mobile, rushed down the flanks of the volcanoes and spread over many square miles of the adjacent regions. The pumice flows were “lubricated” by hot volcanic gas emitted from inside each pumice particle, which buffered it from other particles. Some hot pumice flows were 350 feet deep. The heat still remaining in the pumice after it stopped flowing partly melted the particles to form a hard rock known as welded tuff. Repeated pumice flows buried the hilly landscape and eventually formed a vast volcanic plain. The rocks, which are mostly welded tuffs, are now the Stevens Ridge Formation, which you can see along the highway in Stevens Canyon 1-2 miles west of Box Canyon. You can recognize the welded tuff by its light-gray to white color and its many flattened and sharp-edged inclusions of darker gray pumice (fig. 2). Another period of volcanism followed, of still a different kind, when lava flowed outward from broad low volcanoes. The flows were of two kinds: basalt, the kind now erupted by Hawaiian volcanoes, and andesite, the type erupted by Mount Rainier. Individual flows 50-500 feet thick were stacked on top of one another to a total depth of fully 2,500 feet. We know these rocks as the Fifes Peak Formation. They form many of the cliffs and peaks in the northwestern part of the park. You can examine them in cuts along the Mowich Lake Road between Mountain Meadows and Mowich Lake. The time of the eruption of the Fifes Peak lavas may have been between 20 and 30 million years ago. When the Fifes Peak volcanoes finally became extinct, this part of western Washington changed again. The rocks once more were uplifted and compressed into broad folds parallel to those formed at the end of Ohanapecosh time. The rocks buckled and, in places, broke and shifted thousands of feet along great fractures, or faults. [Illustration: Outcrop of light-gray welded tuff in the Stevens Ridge Formation along the road in Stevens Canyon. The angular dark-gray fragments in the welded tuff are chunks of pumice. (Fig. 2)] About 12 million years ago one or more masses of molten rock, many miles across, pushed upward through the Puget Group and younger rocks. When this molten rock cooled and hardened, it formed granodiorite, a close relative of granite. Although most of the molten rock solidified underground, some of it reached the land surface and formed volcanoes at a few places within the area of Mount Rainier National Park. [Illustration: Granodiorite looks like granite and has a light-gray speckled appearance. The knife is about 3 inches long. (Fig. 3)]