During the period of gigantic mountain building millions of years ago, the ancient peak Mount Si was covered by the Cascades, but never has there been real conformity between the hard primeval rock and the younger volcanic formation. The younger rock slips from time to time, as some earth movement takes place, and the resultant tremendous jar is felt throughout the region.
In the Proterozoic era, the earliest of the four geologic divisions of time, long before the Cascades had risen, an embayment of the primeval sea covered most of the Pacific Northwest region. The Blue Mountains, in the extreme southeastern corner of the present State, have been described by some geologists as a rocky promontory extending into this arm of the sea. Some 300 or more miles to the west of the old coastline, south from what is now Washington, lay an island, or islands, the existence of which has led to the erroneous belief that another continent lay to the west of this one in prehistoric ages.
After hundreds of millions of years, with alternating periods of submersion and dry land, the region was invaded by the sea from the north, in the Paleozoic era. The depositing of silt from adjacent land areas and other natural processes resulted in the filling up of the original embayment to a maximum depth of 30,000 feet. Present deposits of quartz, slate, marble, and schist represent these ancient ones, but greatly altered in structure and recrystallized. Paleozoic rocks found in various places across northern Washington contain valuable fossil specimens of marine life of that period.
During the Mesozoic era, which probably lasted for more than 100,000,000 years, the essential features marking the existing topography were formed. It was during the latter part of this era (Jurassic period), according to John Hodgdon Bradley, that the original uplift of the Sierra Nevada, the Coast Range, the Cascades, and the Klamath Mountains occurred. Also in this period, another great inundation laid down beds of mud and sand that gradually were transformed into the bedrock of the San Juan Islands. Large deposits of magnesite, especially in Stevens County, probably originated at this time. With the making of mountains, great masses of molten rock pressed upward through the earth's crust, and gold, silver and other metals were fused with the rock while in this liquid state. As the Cascades first, and later the Coast Range, were formed, successively they made new coastlines, low-lying barriers to the ocean. The Mesozoic era, the age of reptiles, gave to the world some of its most curious life forms, including the giant dinosaurs; many of these have been unearthed on the San Juan Islands and in other parts of the State. Many marine specimens have been found in the shales and limestones of Stevens County.
The latest era, the Cenozoic, was marked by some of the most dynamic changes of all, including the greatest lava flow in geologic history and the age of ice; it also gave to the region some of its most productive natural resources -- rich soil left by extensive lava flows, the great rivers and bays taking shape during this period, and the rich deposits of coal and other minerals being laid down. Of this era, the last 2,000,000 years constitute the recent epoch, within which came great volcanic eruptions and the period of glaciation. The Tertiary period, enduring for more than 50,000,000 years, was marked by long periods of sedimentation, erosion, and vegetation, alternating with periods of immense volcanic activity.
The western part of the State, except for the highest, or central, part of the Olympic Mountains, was covered with water, and great swampy flats extended along the edge of the present Puget Sound Basin. From these were derived the shales and sandstones, the gold-bearing gravel of Sauk River, the commercial coal deposits. Gradually the see floor was raised, and the Olympics were united with the mainland. Volcanic action, accompanying the building of the Columbian Plateau, brought forth great streams of lava, covering more than 200,000 square miles (estimates vary) in present Washington, Idaho, and Oregon. The weight of hot plastic rock tended to wear away all but the highest bills and to force streams to seek new outlets, with the changing of the watershed. The Columbia River was forced from its old channel into its present one, cut through granitic slopes at the edge of the lava plain.
With the cessation of volcanic activity, in the long periods of sedimentation and erosion, many forms of animal and reptile life inhabited the region. Immense forests arose; petrified logs remain to indicate something of the size and type of these ancient trees. Gingko Petrified Forest was formed by the flow of lava over fallen gingko, trees; ground water creeping through the rock brought quantities of silica which, in the form of quartz, gradually took the place of the wood. Whole stone logs are found, some wonderfully and delicately colored, in the shape of the Asiatic gingko tree.
Toward the close of the Tertiary period, various plateaus and hills were formed -- the Badger Mountains and Waterville Plateau, prominent folds of the Frenchman Hills, and the Spokane Divide. Large basins were created, and the Yakima River cut its way through ridge after ridge, as each in turn arose.
The Quaternary (later Cenozoic) period was one of discordant events that completely changed the topography, producing marked climatic differences between eastern and western Washington. From a chain of vents along the line of the Cascade Mountains, volcanoes discharged great quantities of cinders and ash and exuded molten rock. Temporary cessations of the latter allowed incrusting materials, chiefly andesite, to build up great cones to form such peaks as Baker, St. Helens, Adams, and Rainier. The largest of these was the truncated mass of Mount Rainier. Active as late as the early part of this century and still steaming and emitting gases, this mountain once attained a height of more than 16,000 feet, only to lose 2,000 feet of its peak in an explosion. Other unrelated lava flows occurred at this time throughout the Cascade Mountains.
Later, as the climate turned colder, enormous glaciers slid down from the north to cover the upper part of the State. Elevations were greater than now. Puget Sound was dry. On the lofty Cascade Mountains and the major volcanic peaks, constant snows packed into glaciers that plowed down the slopes.
With a reversion to comparative warmth, melting ice sent debrisladen floods roaming over the Columbian plain, seeking or creating new channels as they rushed down the gradients caused by an earlier tilting. The abandoned rock-walled channels are today known as coulees. The Columbia River, much greater in volume than it is today, was blocked by the Okanogan Ice Lobe at the present site of Coulee Dam. The powerful stream, augmented by the run-off from adjacent and distant glaciers and the sudden draining of large lakes as far east as Montana, excavated a new channel. Abandoned when the retreating glacier allowed it to resume its former course, the old channel is now known as the Grand Coulee. A waterfall, one of the greatest in earth's history, thundered over the cliffs in what is today Dry Falls State Park.
A great lake, named by geologists Lewis Lake, and many minor bodies of water covered large areas of central and eastern Washington. The White Bluffs, 600 feet high and 30 miles long, on the Columbia River in Franklin, Grant, and Benton Counties, were created at this time. The force of the streams stripped sediments from the underlying lava, and these, transported southward, fill the fertile farming areas today. The denuded regions are the Channeled Scablands, more than 2,500 square miles of bare lava intricately channeled by ancient streams, now dry.
The shallow edges of the glaciers in the Puget Sound region, reaching as far south as Tenino, melted quickly, forming "mystery mounds" -- the hundreds of little hummocks and hills of that "mound prairie" region. Vast clay deposits, characteristic of Puget Sound topography south of Admiralty Inlet and Deception Pass, indicate a damming of the melting waters at these points. With the disappearance of the ice dams, the quick run off carved numerous valleys out of the sea bed. When the sea level rose again these became deep harbors and channels bordered by high cliffs.
Fossils found in central Washington beds tell of lush vegetation and abundant animal life -- temperate zone and subtropical flora and fauna -- maintained by the rich lava-formed soil. Fossilized leaves of fig, oak, cypress, elm, and gingko (the Sacred Tree of China) have been uncovered. Sequoia trees grew in several parts of the State.
Rocks along the margins of Puget Sound have revealed marine forms of the recent, or Cenozoic, era. Bones of mammals of this period, including the mammoth, the horse, and the bison, may be seen in the Whitman College Museum at Walla Walla. A skeleton of the mastodon (Elephas Columbi), built up from remains uncovered in the vicinity of Latah near Spokane in 1878, is a highly valued exhibit in the Field Museum in Chicago.