Mammals of Washington, Volume 2 University of Kansas Publications Museum of Natural History — Reading Companion

n and deformation. In the early Pleistocene the five great volcanic cones of the Cascades, Mount Baker, Glacier Peak, Mount Rainier, Mount Adams and Mount St. Helens were formed. In eastern Washington a gentle folding of the Miocene lava flows occurred. The folding took place slowly and the Columbia River in its course along the eastern edge of the Cascades cut through the folds as they formed, making a series of water gaps. Farther south, the Simcoe-Frenchman Hills anticline seems to have arisen more rapidly and the Columbia River was forced eastward before it became impounded and rose over the barrier and plunged down, tearing out the great Wallula Water Gap (Flint, 1938). This gap is a mile wide, eight miles long and, in places, a thousand feet deep. The impounding of the Columbia by the Simcoe-Frenchman Hills anticline resulted in a lake several hundred miles in area. Sediments deposited in this lake form the Ringold formation. The Ringold formation possesses a very early Pleistocene mammalian fauna.

The Pleistocene was a time of great change in the mammalian fauna of the world. Unfortunately the beautiful glacial sequence revealed in Europe and the Mississippi Valley cannot be detected in Washington. In western Washington the deposits of the last continental glaciation and fluvial deposits of the last interglacial period almost everywhere obscure evidence of earlier glaciations. Deposits of an earlier glaciation, named Admiralty by Bretz (1913), have been detected in places. Deposits of greater age, that may represent a still earlier glaciation, have been noted. In eastern Washington the only definite proof of multiple glaciation is of one glaciation preceding the last. This is the Spokane glaciation of Bretz (1923). That multiple glaciation in the sequence reported from the Mississippi Valley affected Washington seems probable. The lack of evidence of a complete sequence is negative evidence. In western Washington the earliest glacial deposits might be beneath the later deposits or they may have been removed or reworked by subsequent glaciations, whereas in eastern Washington they may have been removed by subsequent glaciation and erosion.

The time interval between the two known glaciations appears to have been of greater duration than the Recent. The drift of the earlier period is sometimes found covered by the till of the later glaciation, and preserved by it. The early material is deeply weathered and all save the hardest pebbles and quartzites, for example, are rotten and disintegrate at the touch. In contrast, the later deposits are almost unweathered. Pebbles are hard, and ring when struck. A zone of leaching and oxidation of the finer materials reaches a depth of some 30 inches, below which the till is fresh.

Two names are currently applied to the last continental glaciation of the state of Washington. That west of the Cascade Mountains, studied and described by Bretz (1913), was termed "Vashon." The interglacial cycle preceding it was called "Puyallup." The glaciation of eastern Washington has been called "Wisconsin," after the Mississippi Valley terminology, by several writers. Papers by Flint (1935, 1937) describe and map it.

The Vashon and Wisconsin glaciations probably occupied the same time interval, although this has not certainly been established. In the present report I have used the term "Vashon-Wisconsin" in speaking of the entire period, or the glaciers both east and west of the Cascades together. Vashon, alone, is restricted to western Washington and Wisconsin to eastern Washington.

The Vashon glaciation seems to have consisted of an ice dome centering in Puget Sound (the Puget Glacier of Bretz, 1913) and flooding the lowlands from the Olympic Mountains to the Cascade Mountains. The southern edge of the Puget Glacier was slightly south of the present terminus of Puget Sound. Fingerlike projections of ice were forced up valleys of the western Cascades and the northern and eastern Olympics. Some of these upward moving fingers of ice met and coalesced with valley glaciers descending from the mountains. At the southern edge of the glacier, the Black Hills and Porcupine Hills remained above the ice although partially surrounded by it.

The Wisconsin glacier, according to Flint (1935), was a great piedmont glacier, fed by valley glaciers from the Cascades and Coast Ranges to the west and the Rockies to the east. It extended from the Idaho boundary to the Cascade Mountains. From the Canadian Boundary it sloped down to an approximate elevation of some 6500 feet at Republic and to 2500 feet on the northern edge of the Columbian Plateau which was the southern edge of the glacier. The Kettle River Mountains, in almost the center of the glacier, remained a peninsula or driftless area that divided the glacier into two lobes. The Pend Oreille, Huckleberry and other mountain ranges, formed nunataks, or islands above the ice, at the southern part of the glacier.