species of mammals occurring in Washington decreases rapidly as we go
back in time. The distribution of the modern fauna at the present time
is fairly well known. The distribution of species 100 years ago is less
well understood. This is especially true of certain game species and
carnivores whose distribution has been altered by man. Our knowledge of
the distribution of mammals in the Pleistocene and earlier times is
based on fossil skeletons. Such knowledge must necessarily be meager,
for conditions favorable to fossilization and the preservation of
fossils until their subsequent discovery by man, were not of common
occurrence.
In the Cascades and in eastern Washington, the Miocene was a time of
orogeny and great volcanism. Great flows of lava, 4,000 feet thick in
the Snake River area (Russell, 1893), emerging from fissures in the
Snake River area, formed the Columbian Plateau. The Columbian basalt
slopes inward centripetally from the eastern, northern, and western
margins of the Columbian Plateau with an average descent of 25 feet to
the mile (Flint, 1938). The dip of the lava flows results in the
basalt-marginal course of the Spokane and Columbia rivers today, along
the northern edge of the Columbian Plateau. The earlier part of the
Pliocene was a period of erosion 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.
[Illustration: FIG. 17. Extent of Vashon-Wisconsin ice over
Washington. The Wisconsin and Vashon glaciers have been connected
through the Mount Rainier section of the Cascades because it is
thought that few or no mammalian species lived in the Cascades north
of Mount Rainier while the ice was in place. Data generalized from
Flint (1937), Bretz (1913), Culver (1936) and other sources.]
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.
The behavior of valley glaciers in the northern Cascade Mountains
during Vashon-Wisconsin time, seems to have been variable. Some
depression of the snow line, at least in the north, seems probable.
The Vashon Glacier impinged on the eastern, northern and to some extent
the western, slopes of the Olympic Mountains. Late Pleistocene valley
glaciers in the Olympics, however, seem to have been inconsequential.
The time of the retreat of the Vashon-Wisconsin glaciers is a subject
of special interest to the mammalogist in that it represents time for
invasion and dispersal of species and in that it represents generations
of individuals upon which natural selection might act. It is generally
agreed that a period of approximately ten thousand years has elapsed
since the retreat of the Vashon-Wisconsin glaciers from Washington.
Information on the climate of the state of Washington previous to the
period of the last continental glaciation is understandably meager.
Bretz (1913) considers the Puyallup period a time of excessive
precipitation and erosion. Bits of lignite from Puyallup sediments
seem to be of Douglas fir. Presumably the climate was slightly warmer
and more humid than it is today. Vegetation possibly consisted of
coniferous forests.
With the advance of the Vashon ice, mammals north of the ice border
were all or mostly eliminated. Climatic conditions south of the border
of the ice probably were strongly affected by it. Remains of mammoths
have been found in Vashon till. The presence of many non-boreal species
of mammals in southwestern Washington indicates their persistence
there and that conditions therefore were not intolerable for them.
Probably the climate of southwestern Washington was cool and dry. Fir,
spruce, and Douglas fir may have been the dominant trees. Hansen (1941
A: 209) found evidence from studies of pollen that coniferous forests
were growing in west-central Oregon in late glacial time. These pollen
studies of postglacial peat bogs by Henry P. Hansen give evidence of
postglacial climatic changes. Hansen points out (1941 B, 1941 C) that
climatic changes west of the Cascades were probably slight because of
the influence of the Pacific Ocean. Pollen profiles indicate an early,
cool, dry climate followed by a warmer one and increasing humidity.
The present climate may be considered cool and humid. Most of western
Washington lies in the Humid subdivision of the Transition Life-zone.
[Illustration: FIG. 18. McDowell Lake, Little Pend Oreille Wildlife
Refuge, Stevens County, Washington, September 29, 1939. (Fish and
Wildlife Service photo by Victor B. Scheffer, No. 730.)]
The pre-Wisconsin climate of eastern Washington is unknown. From
the loessial nature of the Palouse Soil (Bryan, 1927), a preglacial
deposit, the area would seem to have been arid, probably a grassland or
a sagebrush desert. If the fossil fauna discovered at Washtuckna Lake,
Adams County, is of this period, the forest conditions of the Blue
Mountains were slightly more extensive than at present. The glacial
climate of the Columbian Plateau in Wisconsin time was probably cool
and arid. Pollen studies by Hansen (1939, 1940) indicate increasing
dryness and warmth since the retreat of the Wisconsin ice. Present-day
climate on the Columbian Plateau is warm and dry. The plateau is
principally a sagebrush desert. The glaciated area to the north is
cooler and more humid, supporting extensive forests of yellow pine and
other conifers.
THE FAUNAS
We have mentioned elsewhere that three different mammalian faunas occur
in Washington. These may be described as follows.
1. THE GREAT BASIN FAUNA. This fauna is best typified by such genera as
_Perognathus_ and _Dipodomys_. Species that, at least in Washington,
are confined to this fauna are:
_Sorex merriami_ _Tamias minimus_
_Myotis thysanodes_ _Perognathus parvus_
_Myotis subulatus_ _Dipodomys ordii_
_Pipistrellus hesperus_ _Onychomys leucogaster_
_Antrozous pallidus_ _Reithrodontomys megalotis_
_Taxidea taxus_ _Lagurus curtatus_
_Marmota flaviventris_ _Lepus californicus_
_Citellus townsendii_ _Sylvilagus nuttallii_
_Citellus washingtoni_ _Sylvilagus idahoensis_
The break between the Great Basin Fauna and the other two faunas is
extremely sharp, probably as a consequence of a sharp break in the
flora.
2. THE PACIFIC COASTAL FAUNA. The mammals of the humid coastal district
range from the Fraser River, British Columbia, southward to the
vicinity of Monterey Bay, California. In Washington typical genera are
_Aplodontia_, _Neurotrichus_ and _Scapanus_. The following species are
typical of the Pacific Coastal Fauna in Washington:
_Neurotrichus gibbsii_ _Tamiasciurus douglasii_
_Scapanus townsendii_ _Sciurus griseus_
_Sorex trowbridgii_ _Clethrionomys californicus_
_Sorex bendirii_ _Microtus townsendii_
_Marmota olympus_ _Microtus oregoni_
_Tamias townsendii_ _Aplodontia rufa_
Some species which range outside this faunal area have strongly marked
races confined to it. _Glaucomys sabrinus oregonensis_ and _Lepus
americanus washingtonii_ are examples. The Pacific Coastal Fauna is a
forest fauna. Like the Great Basin Fauna, it reaches its northern limit
of distribution in Washington and is better represented farther south.
Unlike the Great Basin Fauna, the break between the Pacific Coastal and
the surrounding fauna is not sharp, because forests continue into the
more boreal faunal areas to the north and east. There, some mingling of
coastal and Rocky Mountain faunas occurs.
3. ROCKY MOUNTAIN FAUNA. If this fauna be thought of as including
mammals of the Rocky Mountains of the United States, and also those of
the subarctic faunal area to the east of these mountains in Canada, the
species in Washington are as follows:
_Sorex palustris_ _Synaptomys borealis_
_Microsorex hoyi_ _Phenacomys intermedius_
_Lynx canadensis_ _Clethrionomys gapperi_
_Marmota caligata_ _Microtus richardsoni_
_Citellus lateralis_ _Ochotona princeps_
_Citellus columbianus_ _Lepus americanus_
_Tamias amoenus_ _Rangifer montanus_
_Tamiasciurus hudsonicus_ _Oreamnos americanus_
_Glaucomys sabrinus_
Of the three, the Great Basin Fauna is the most distinct. Only about
twenty species which occur within the Great Basin Faunal Area, occur
also outside of it in one or both of the two other faunal areas. Most
of these twenty are subspecifically different in the Great Basin Faunal
Area as contrasted with one or both of the other areas. Each of the
other two areas has no less than 32 species that are not restricted to
it.
SPECULATION AS TO EMIGRATIONAL HISTORY OF THE MAMMALS
The present fauna of the state of Washington was derived in part from
Asia and in part from native forms. Great changes occurred in early
Pleistocene through emigration. By the late Pleistocene most of the
mammals now occurring in the state of Washington were as they are
today. The greatest changes that seem to have occurred in the late
Pleistocene are the extinctions of numerous groups, locally or totally.
Among the carnivores, Matthew (1902: 321) reports remains of the great
lion, _Felis atrox_, associated with such familiar species as the
badger, cougar, lynx and mountain goat. The great lion was very similar
to the modern African lion but was fully a fourth larger. Associated
with the great lion in the California tar pits are the carnivorous
short-faced bears (_Tremarctotherium_), as large as the Alaskan
brown bears; dire wolves (_Aenocyon_), larger than timber wolves;
and saber-tooth tigers (_Smilodon_). These forms were probably also
present in Washington in the late Pleistocene. Matthew (_loc. cit._)
reports remains of the giant beaver, _Castoroides_, from the Silver
Lake deposit of Oregon. This great beaver, as large as a black bear,
was doubtless a resident of Washington also. Peccaries, camels, bison,
horses and giant ground sloths have been recorded from Pleistocene
deposits of Washington and nearby areas. Of the elephant tribe, the
mastodon and several species of mammoths were present.
These extinct forms have doubtless exerted some influence on the past
distribution of mammals in Washington and possibly have had an effect
on the distribution of members of the living fauna. One species of the
mammoth, at least, existed in Washington in postglacial time. Remains
of this form, _Elephas columbi_, have been found in Vashon till.
The three faunas of Washington can be placed in two categories. One is
Sonoran, essentially a desert type, and occupies the Columbian Plateau.
The other two are forest faunas, predominantly boreal in complexion,
and are closely related. The Rocky Mountain Fauna is found in the Blue
Mountains and in northeastern Washington. The Pacific Coastal Fauna is
found in western Washington.
The ice sheets of Vashon-Wisconsin time descended southward to southern
Puget Sound and to the northern edge of the Columbian Plateau. If the
area of the ice sheet be superimposed on a map of distributional areas
of Washington, it is seen that the area occupied by the Rocky Mountain
Fauna in northeastern Washington is eliminated. Thus, at the maximum
descent of Wisconsin ice, the Rocky Mountain type of mammalian fauna
was found only in extreme southeastern Washington. No point of contact
between the forest fauna of the Rocky Mountains and the fauna of the
Pacific coast exists, anywhere, because desert areas, or at least
barren plains, lie between them from the border of the glaciers south
to Mexico. For the entire period, perhaps thousands of years long,
while the glaciers were in place, the two forest faunas were separated.
Repeated separation of the faunas by successive glaciations is thought
to be responsible for many of the differences now existing between them.
Following the retreat of the ice, the Pacific Coastal Fauna extended
its range northward to the Fraser River and, in part, into the Cascade
Mountains. The Rocky Mountain Fauna invaded northeastern Washington and
boreal Canada, including the Pacific Coast north of the Fraser River.
Certain parts of the Rocky Mountain Fauna also invaded the Cascade
Mountains.
Inasmuch as the Cascades were invaded by species from both faunas, a
detailed analysis of the mammals existing there now seems justified.
Several significant features of the composition of the mammal fauna
of the Cascades are apparent. First, several species typical of the
Pacific Coastal Fauna are present, such as _Neurotrichus gibbsii_,
_Sorex trowbridgii_, _Sorex bendirii_, _Tamias townsendii_, _Microtus
oregoni_ and _Aplodontia rufa_. Each of these species has no close
relatives in the Rocky Mountain Fauna and, save perhaps _Sorex
trowbridgii_, occupies a unique ecological niche and has no counterpart
in the Rocky Mountain Fauna.
A second group includes species with close relatives in both the Rocky
Mountain and Pacific Coastal faunas. This group is remarkable in that it
is composed of either very closely related species or very strongly
differentiated subspecies in each fauna. For example, the golden-mantled
ground squirrel (_Citellus saturatus_) of the Cascade Mountains is
specifically distinct from _Citellus lateralis_. Supposedly the Cascade
form was isolated in the southern Cascades during Vashon-Wisconsin time.
The Douglas squirrel (_Tamiasciurus douglasii_) of the Cascades, which
has a red belly, is the same as the squirrel of the lowlands of western
Washington but is specifically distinct from the red squirrel
(_Tamiasciurus hudsonicus_) of the Rocky Mountain Fauna, which has a
white belly. In the extreme northeastern Cascades the two species come
together. They do not interbreed but seem to compete, for they do not
occur together. The flying squirrel (_Glaucomys sabrinus fuliginosus_)
of the Cascades is only slightly differentiated from other races of the
Rocky Mountain Fauna but is much different, as are all Rocky Mountain
races, from the western Washington subspecies (_Glaucomys s.
oregonensis_). The red-backed mouse of the Cascades is _Clethrionomys
gapperi_, a species distinct from _Clethrionomys californicus_ of
western Washington. The jumping mouse of the Cascades is _Zapus princeps
trinotatus_, the same race that occurs in western Washington. It is
quite distinct from, and has previously been considered a species
separate from, the races of the Rocky Mountain Fauna. The snowshoe
rabbit of the Cascades is closely related to other races of the Rocky
Mountain Fauna but is distinct from _L. a. washingtonii_ of western
Washington. The pika (_Ochotona princeps_) of the Cascades was
apparently isolated in the southern part of the range during the
glaciation. After the retreat of the glaciers it extended its range
northward. Competition between two subspecies has resulted in parallel
distributions due to relative body size. The two races freely intergrade
and the differences between them are not so great as in the other forms
mentioned.
The third group of mammalian species of the Cascades is composed of
species typical of the Rocky Mountain Fauna such as: _Marmota caligata_,
_Synaptomys borealis_, and _Orcamnos americanus_. Each has no ecological
counterpart in the Pacific Coastal Fauna. Each is absent from the
Cascades of Oregon.
We interpret the mixture of faunas in the Cascades as follows: The
Vashon-Wisconsin ice sheet was in place for a long period of time,
longer, probably, than the Recent. During this time, forest mammals of
the Pacific Coast were isolated from forest mammals farther east by
glaciers to the north and desert to the east. Changes took place in both
of the separated forest faunas. Certain species, perhaps, such as the
mammoth, became extinct. Other forms were exterminated then or at an
earlier time in one fauna or the other. If _Aplodontia_, _Neurotrichus_
or _Scapanus_ occurred in the Rocky Mountain faunal area, it lived in an
inland area of rigorous climate, and disappeared there because it was
unable to adapt itself to the cold. In the mild climate caused by
proximity of the ocean, mild even in Vashon-Wisconsin time to judge from
evidence yielded by study of fossil pollens, primitive forms such as
moles, the Bendire shrew, and mountain beaver persisted along the coast,
where there were no boreal conditions. Some alpine forms, such as
_Marmota olympus_, _Ochotona princeps brunnescens_ and _Citellus
saturatus_ persisted in the Olympic or Cascade mountains as relic
species. On the whole, however, the glacial divergence resulted in a
boreal forest fauna and a temperate forest fauna.
In addition to change in component species, there were evolutionary
changes in the species themselves. In some these were considerable, as
shown by the differences between related forms of the two faunas. In
most species, however, evolutionary changes have resulted in only
subspecific differences.
Following the retreat of the glaciers and the establishment of
vegetation on the deglaciated areas, movements of the faunas occurred.
The Rocky Mountain Fauna spread northward and westward, to northeastern
Washington and, in Canada to the Pacific, occupying most of the land
exposed by the glaciers. The Pacific Coastal Fauna spread northward only
as far as the relatively slight barrier of the Fraser River. The Cascade
Mountains became a "no-man's land." The pika and golden-mantled ground
squirrel of the southern Cascades spread northward. Boreal Rocky
Mountain forms with no ecologic competitors from the Pacific Coastal
Fauna occupied the Cascades. Also, coastal species with no Rocky
Mountain competitors occupied the Cascades. Nevertheless, some
competition between members of the two faunas ultimately occurred, and
in instances where closely related forms occurred in the two faunas, one
or the other prevailed in the Cascade Range. For example, the Douglas
squirrel and big jumping mouse are now established in that range, but
the relative of each occurring in the Rocky Mountains is present in the
extreme northeastern Cascades. It is possible that in these two cases,
the related form occurring in the Rocky Mountains has just entered the
area and that competition has just begun. With regard to the flying
squirrel, red-backed mouse and snowshoe rabbit, the more boreal Rocky
Mountain representatives have definitely displaced the coastal forms.
Certain mass movements of mammals are popularly believed to have
occurred with the advance of the ice sheets of the Pleistocene. The
boreal birds and plants on higher peaks of the Cascades and the Sierra
Nevada of California are thought to represent relics of faunas that
moved northward. Such mass movements probably did occur and there is
some evidence of their occurrence in Washington. Probably the
pre-Wisconsin flora of coastal British Columbia consisted of coniferous
forest similar to that of western Washington today. If this were the
case, the mammalian species in British Columbia corresponded closely to
those of western Washington. An influx of such a fauna into coastal
Washington would scarcely be evident today if, indeed, it was noticeable
even then. In eastern Washington, forest species forced southward would
come upon the barren, inhospitable plains and deserts of the Columbian
Plateau.