The Geologic History of The Geologic History of Washington State & Washington State &

Kittitas CountyKittitas County

Jana Jones MabryJana Jones Mabry

Geologic History of Geologic History of Washington StateWashington State

Overview of the processes Overview of the processes responsible for the underlying responsible for the underlying geologygeology

Overview of different geologic Overview of different geologic provinces of the stateprovinces of the state

Overview of the geology specific to Overview of the geology specific to the area of Snoqualmie Pass and the area of Snoqualmie Pass and Lake Easton State ParkLake Easton State Park

The Geologic Processes responsible for The Geologic Processes responsible for the landscape features seen in the landscape features seen in

WashingtonWashington

Plate TectonicsPlate Tectonics– VolcanismVolcanism– lava flowslava flows

GlaciationGlaciation– Alpine GlaciersAlpine Glaciers– Massive Flood EventsMassive Flood Events

Weathering and ErosionWeathering and Erosion

Plate TectonicsPlate Tectonics The theory and study of the The theory and study of the

earth that describes the earth that describes the processes of continental processes of continental formation and movements. formation and movements.

It proposes explanations for It proposes explanations for how, why, and when how, why, and when continents are built and continents are built and how they move.how they move.

It is the process responsible It is the process responsible for the physical conveyance for the physical conveyance of materials that form the of materials that form the bedrock geology of bedrock geology of Washington State.Washington State.

VolcanismVolcanism

Three types of volcanic processes are Three types of volcanic processes are associated with Washington Geologyassociated with Washington Geology

– Batholiths and plutonsBatholiths and plutons– Magma trapped and cooled under the surface.Magma trapped and cooled under the surface.

– VolcanoesVolcanoes Magma that escapes through a vent in an explosive Magma that escapes through a vent in an explosive

event or the repeated rise of magma to the surface. event or the repeated rise of magma to the surface.

– Plateau Basalt ProvincesPlateau Basalt Provinces

Glaciation Glaciation

The accumulation and movement of flowing ice.The accumulation and movement of flowing ice. In Washington the most significant glaciers In Washington the most significant glaciers

occurred between 1.6 million years ago to about occurred between 1.6 million years ago to about 10,000 years ago.10,000 years ago.– The glaciers carved sharp features in the high peaksThe glaciers carved sharp features in the high peaks– created glacial troughs, lakes, and ice dams that led to created glacial troughs, lakes, and ice dams that led to

massive flood eventsmassive flood events– deposited glacial debris called till and loess along their deposited glacial debris called till and loess along their

pathspaths

Overview of the Geologic Overview of the Geologic History of Washington StateHistory of Washington State

The oldest rocks in Washington State The oldest rocks in Washington State are part of the 1 billion year old Belt are part of the 1 billion year old Belt

SupergroupSupergroup

The North American The North American Continental Continental Coastline was Coastline was located located approximately 30 approximately 30 miles west of the miles west of the the present day the present day border of Idaho border of Idaho and Washingtonand Washington

The continued addition of material to the The continued addition of material to the North American Continent was through North American Continent was through

the process of Platethe process of Plate TectonicsTectonics

Plate tectonics Plate tectonics conveyed small conveyed small volcanic islands and volcanic islands and fragments of other fragments of other continents called continents called terranes onto the terranes onto the North American North American Continent and Continent and accreted them in the accreted them in the area of the existing area of the existing coastline. coastline.

The first terrane to arrive was the Okanogan The first terrane to arrive was the Okanogan Micro-continent at 190 to 160 million years Micro-continent at 190 to 160 million years

agoago

This micro-continent This micro-continent crushed the coastal crushed the coastal plain that had been plain that had been building for 600 million building for 600 million years (800 to 200 years (800 to 200 myBP) between the myBP) between the North American North American Continent and the Continent and the Okanogan creating an Okanogan creating an area of displaced area of displaced marine sedimentary marine sedimentary materials called the materials called the Kootenay ArcKootenay Arc

The next major addition occurred 90 to 100 The next major addition occurred 90 to 100 million years ago with the arrival of the North million years ago with the arrival of the North

Cascade TerranesCascade Terranes

The North Cascade The North Cascade Terranes are believed Terranes are believed to be made up of a to be made up of a group of 6 different group of 6 different islands.islands.

Each individual terrane Each individual terrane can be distinguished can be distinguished by its unique rock by its unique rock type.type.

These terranes were These terranes were covered later by covered later by volcanic materials and volcanic materials and complicated their complicated their interpretation.interpretation.

The Insular Terrane arrived behind the North The Insular Terrane arrived behind the North Cascade Terranes at about 100 million years Cascade Terranes at about 100 million years

agoago

This terrane is This terrane is believed to have believed to have been two large been two large pieces that pieces that make up the make up the basement rocks basement rocks under the San under the San Juan Islands and Juan Islands and the Blue the Blue MountainsMountains

The last event to add to the Washington coastline was The last event to add to the Washington coastline was approximately 25 million years ago is called the approximately 25 million years ago is called the

Crescent Terrane located in the areas of the Puget Crescent Terrane located in the areas of the Puget Lowlands, Olympic Peninsula and the Willapa HillsLowlands, Olympic Peninsula and the Willapa Hills

The Crescent Terrane is The Crescent Terrane is believed to be a portion of believed to be a portion of ocean crust that was ocean crust that was stranded between an extinct stranded between an extinct trench and the present day trench and the present day trench. Some how more trench. Some how more buoyant rocks were carried buoyant rocks were carried underneath the continental underneath the continental crust, then escaped pushing crust, then escaped pushing the overlying rocks as much the overlying rocks as much as 2 miles above the ocean as 2 miles above the ocean crustcrust

More Changes occurred to the landscape More Changes occurred to the landscape with the eruptions of the Columbia River with the eruptions of the Columbia River Basalt Group between 17.5 to 6 million Basalt Group between 17.5 to 6 million

years agoyears ago

These basalt lava flows These basalt lava flows originated from dike originated from dike swarms and cracks in swarms and cracks in the earth called fissures the earth called fissures in the area where in the area where Washington, Oregon and Washington, Oregon and Idaho come togetherIdaho come together

Lava flowed out onto the Lava flowed out onto the surface in 120 individual surface in 120 individual flows covering 100s of flows covering 100s of square miles of this square miles of this regionregion

Pleistocene ice sheets and glaciers that Pleistocene ice sheets and glaciers that occurred from 2 million to 500 years agooccurred from 2 million to 500 years ago

The area we are in was The area we are in was carved by the glaciers carved by the glaciers and the sharp features and the sharp features on the high peaks are on the high peaks are called aretes, horns, called aretes, horns, cirques and hanging cirques and hanging valleys. valleys.

Many of the lakes were Many of the lakes were created by the glaciers created by the glaciers and glacial outwash and glacial outwash called till and loess called till and loess blanket the region.blanket the region.

The last significant volcanic events to shape The last significant volcanic events to shape the Washington landscape were the birth of the Washington landscape were the birth of

the Cascade Volcanoes between 1 million and the Cascade Volcanoes between 1 million and 75,000 years ago75,000 years ago

Creation of the Cascade Creation of the Cascade Volcanoes was a direct Volcanoes was a direct result of plate tectonics result of plate tectonics and the subduction of the and the subduction of the Fallaron Plate under the Fallaron Plate under the western coast of North western coast of North America. America.

The volcanoes were The volcanoes were created in a progressively created in a progressively northern direction northern direction beginning in Northern beginning in Northern California and now California and now extending into Canada.extending into Canada.

The Cascade Volcanoes of Washington The Cascade Volcanoes of Washington were the icing on the cake that make up were the icing on the cake that make up

the geology of the statethe geology of the state

Plate tectonics and the resulting volcanism Plate tectonics and the resulting volcanism remain the most active and significant geologic remain the most active and significant geologic processes that affect geology of Washington. processes that affect geology of Washington.

The Juan de Fuca Plate, is still subducting The Juan de Fuca Plate, is still subducting under the northern-most portion of the North under the northern-most portion of the North American Continent.American Continent.

It is responsible for the earthquakes we It is responsible for the earthquakes we experience, the changes to the topography, experience, the changes to the topography, and controls the energy flow and climatic and controls the energy flow and climatic conditions of the region. conditions of the region.

The Ice Sheet and Glaciers that have occurred over the past The Ice Sheet and Glaciers that have occurred over the past 2million years have had a significant impact on the topography of 2million years have had a significant impact on the topography of this area.this area.The Yakima Glacier flowed from the Snoqualmie Summit to Thorp The Yakima Glacier flowed from the Snoqualmie Summit to Thorp The three depressions now holding Keechelus, Kachess and Cle The three depressions now holding Keechelus, Kachess and Cle Elum Lakes held glaciers that fed into the main stream Yakima Elum Lakes held glaciers that fed into the main stream Yakima Glacier.It created the U-shaped valley in which the present day Glacier.It created the U-shaped valley in which the present day Yakima River flows and covered the bedrock geology of the Yakima River flows and covered the bedrock geology of the whole area with glacial debris and alluvial (water deposited) whole area with glacial debris and alluvial (water deposited) materialsmaterials..

The Glaciers in this region carved the The Glaciers in this region carved the paths and natural depressions now paths and natural depressions now

used as reservoirs for the south-central used as reservoirs for the south-central regionregion

Lake Easton is a man made lake created where Lake Easton is a man made lake created where the Yakima and Kachess Rivers come together. This the Yakima and Kachess Rivers come together. This reservoir was built 1928 through excavation and reservoir was built 1928 through excavation and removal of the glacial till.removal of the glacial till.Its primary function is to supply water for the Its primary function is to supply water for the agriculture of south-central Washington and a variety agriculture of south-central Washington and a variety of recreational activities to the central region. of recreational activities to the central region.

The view to the east of the park provides a The view to the east of the park provides a glimpse into the rich geologic history of the regionglimpse into the rich geologic history of the region

The Rocks of Central The Rocks of Central Washington and Lake Washington and Lake

EastonEaston Volcanic (Igneous)Volcanic (Igneous)

– Intrusive (cooled Intrusive (cooled underground as underground as batholiths) Granitebatholiths) Granite

Mounts Stewart and SiMounts Stewart and Si

Metamorphic (cooked)Metamorphic (cooked)– Ingalls Tectonic Ingalls Tectonic

ComplexComplex Easton SchistEaston Schist

SedimentarySedimentary– Glacial DebrisGlacial Debris– River DepositsRiver Deposits