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America's Volcanic Past
Washington State

"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994
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Map, Location of Washington State

Volcanic Highlights and Features:
[NOTE: This list is just a sample of various Washington State features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of Washington State.]

  • Washington State
  • Washington State Regions
  • Washington State - Brief Geologic History
  • Washington State's Cascade Range Volcanoes
  • Battle Ground Lake
  • Beacon Rock
  • Columbia Plateau
  • Columbia River Gorge
  • Drumheller Channels
  • Fort Spokane Area
  • Ginkgo Petrified Forest
  • Glacier Peak
  • Goat Rocks Volcanic Field
  • Grand Coulee
  • Horsethief Lake State Park
  • Kamiak Butte
  • Lyons Ferry State Park
  • Mount Adams
  • Mount Baker
  • Mount Rainier
  • Mount Rainier National Park
  • Mount Spokane
  • Mount St. Helens
  • Mount St. Helens National Volcanic Monument
  • North Cascades
  • North Cascades National Park
  • Olympic Mountains
  • Olympic National Park
  • Potholes State Park
  • Steamboat Rock State Park
  • Steptoe Butte State Park
  • Underwood Mountain
  • Wallula Gap
  • Wind Mountain

Washington State

Idaho, Oregon, and Washington:
The States of Idaho, Oregon, and Washington, total 248,730 square miles. The area is geologically and topographically diverse and contains a wealth of scenic beauty, natural resources, and ground and surface water that generally are suitable for all uses. Most of the area is drained by the Columbia River, its tributaries, and other streams that discharge to the Pacific Ocean. Exceptions are those streams that flow to closed basins in southeastern Oregon and northern Nevada and to the Great Salt Lake in northern Utah. The Columbia River is one of the largest rivers in the Nation. The downstream reach of the Columbia River forms most of the border between Oregon and Washington.

Excerpts from:
R.L. Whitehead, 1994, Ground Water Atlas of the United States: Idaho, Oregon, Washington: U.S. Geological Survey HA730-H
Washington State Regions

Cascade Range Region:15
This region is one of the most geologically young and tectonically active in North America. The generally rugged, mountainous landscape of this province provides evidence of ongoing mountain-building. The Pacific Mountain System straddles the boundaries between several of Earth's moving plates -- the source of the monumental forces required to build the sweeping arc of mountains that extends from Alaska to the southern reaches of South America. This province includes the active and sometimes deadly volcanoes of the Cascade Range and the young, steep mountains of the Pacific Border and the Sierra Nevada.

Where the Sierra Nevada ends a chain of explosive volcanic centers, the Cascade volcanoes, begins. The Cascades Province forms an arc-shaped band extending from British Columbia to Northern California, roughly parallel to the Pacific coastline. Within this region, 13 major volcanic centers lie in sequence like a string of explosive pearls. Although the largest volcanoes like Mount St. Helens get the most attention, the Cascades is really made up of a band of thousands of very small, short-lived volcanoes that have built a platform of lava and volcanic debris. Rising above this volcanic platform are a few strikingly large volcanoes that dominate the landscape.

Columbia Plateau:15
The Columbia Plateau province is enveloped by one of the worlds largest accumulations of lava. Over 500,000 square kilometers of the Earth's surface is covered by it. The topography here is dominated by geologically young lava flows that inundated the countryside with amazing speed, all within the last 17 million years. Over 170,000 cubic kilometers of basaltic lava, known as the Columbia River basalts, covers the western part of the province. These tremendous flows erupted between 17-6 million years ago. Most of the lava flooded out in the first 1.5 million years -- an extraordinarily short time for such an outpouring of molten rock. It is difficult to conceive of the enormity of these eruptions. Basaltic lava erupts at no less than about 1100 degrees C. Basalt is a very fluid lava; it is likely that tongues of lava advanced at an average of 5 kilometers/hour -- faster than most animals can run. Whatever topography was present prior to the Columbia River Basalt eruptions was buried and smoothed over by flow upon flow of lava. Over 300 high-volume individual lava flows have been identified, along with countless smaller flows. Numerous linear vents, some over 150 kilometers long, show where lava erupted near the eastern edge of the Columbia River Basalts, but older vents were probably buried by younger flows.

Rocky Mountains:15
The Rockies form a majestic mountain barrier that stretches from Canada through central New Mexico. Although formidable, a look at the topography reveals a discontinuous series of mountain ranges with distinct geological origins. The Rocky Mountains took shape during a period of intense plate tectonic activity that formed much of the rugged landscape of the western United States. Three major mountain-building episodes reshaped the west from about 170 to 40 million years ago (Jurassic to Cenozoic Periods). The last mountain building event, the Laramide orogeny, (about 70-40 million years ago) the last of the three episodes, is responsible for raising the Rocky Mountains.

Washington State - Brief Geologic History

Washington State Geology:14
Washington is uniquely positioned for the study of the geologic and structural setting of western North America. To the southeast, in Oregon and Nevada, extensional features predominate as reflected by basin-and-range terrain. To the east, the Rocky Mountains influence the geology of Idaho. To the north, western British Columbia is characterized by a massive coastal crystalline belt and remnants of the geologic continent Wrangellia. All of these major crustal features of the adjacent regions terminate in Washington. The state's uniqueness is further enhanced by two major geologic conditions. First, Washington is impacted by crustal tectonics as the oceanic Juan de Fuca plate is being forced under the North American continent through a process called subduction. Second, the Columbia Basin in Washington and adjacent Oregon was subjected to one of the greatest outpourings of basalt known in the geologic record. Washington's geology is highly diverse. Rocks of Precambrian age, as well as units from every geologic period, Cambrian to Quaternary, are represented. The area of the state has been subject to continental collisions, metamorphism, intrusion of igneous rocks, volcanism, mountain-building episodes, erosion, and massive flooding events. This diversity has a strong influence on soil productivity, location of mineral deposits, scenic grandeur, and even the climate.

Rocks of Idaho, Oregon, and Washington State:20
The rocks and unconsolidated deposits in Idaho, Oregon, and Washington range in age from pre-Tertiary to Holocene.

Unconsolidated Deposits:20
Unconsolidated deposits extend over large areas and differ considerably in age and grain size. They consist of younger, coarse-grained deposits of chiefly stream or glacial origin and older, fine-grained deposits of chiefly lake, volcanic, or eolian (wind blown) origin. In places, older unconsolidated deposits contain thick beds of volcanic ash; in other places, these deposits contain thin (a few feet to a few tens of feet) flows of basaltic or silicic volcanic rocks. Older unconsolidated deposits usually become increasingly compacted with depth. In southwestern Idaho and southeastern Oregon, older unconsolidated deposits are difficult to distinguish from silicic volcanic rocks where the latter are present as thick beds of ash.

Volcanic Rocks:20
Volcanic rocks range in composition from basaltic rocks that are dense, fine grained, dark colored, and contain large quantities of iron and manganese to silicic volcanic rocks that generally are coarse grained, light colored, and contain large quantities of silica. Some basalt flows on the Snake River Plain in Idaho are less than 2,000 years old, as are some in the Cascade Range in Oregon and Washington. The latest volcanism was the 1980 eruption of Mount St. Helens in south-central Washington.

Pre-Miocene Undifferentiated Rocks:20
Pre-Miocene rocks consist of undifferentiated volcanic rocks, undifferentiated consolidated sedimentary rocks, and undifferentiated igneous and metamorphic rocks that are distributed throughout the three states, principally in the mountainous areas. In some places, the thickness of the volcanic rocks might be as much as about 5,000 feet and that of the consolidated sedimentary rocks might be as much as about 15,000 feet. The thickness of the igneous and metamorphic rocks is unknown. The undifferentiated volcanic rocks, which are present in all three States, are a heterogeneous mixture that ranges from basaltic to rhyolitic in composition and commonly are thick flows. These rocks can be similar to some younger volcanic rocks but usually are more dense and contain few fractures. Undifferentiated consolidated sedimentary rocks, which are present primarily in western Oregon and southwestern Washington, consist chiefly of limestone, dolomite, sandstone, and shale. Because some of these rocks were deposited in a marine environment, they might contain saltwater, particularly west of the Cascade Range in Oregon and Washington. East of the Cascade Range, the aquifers in pre-Miocene rocks generally yield freshwater but locally yield saltwater. The undifferentiated igneous, metamorphic, and sedimentary rocks, which are present in all three States, generally are dense and contain few fractures.

Miocene Volcanic Rocks:20
Miocene basaltic rocks commonly are thick, solid flows that are widespread in southwestern Idaho, eastern Oregon, and south-central Washington. Miocene basaltic-rock aquifers consist primarily of thick basaltic lava flows. The aquifers are most productive in the Columbia Plateau of northeastern Oregon and southeastern Washington where the aquifers are thickest. The maximum thickness of the aquifers is estimated to be as much as about 15,000 feet in the southern part of the Columbia Plateau. These aquifers generally yield freshwater but locally yield saltwater. Most of the fresh ground-water withdrawals are used for agricultural ( primarily irrigation) purposes.

Miocene Basaltic-Rock Aquifers:20
Miocene basaltic-rock aquifers consist primarily of flood-type basaltic lava flows that were extruded from major fissures; some flows extend along former lowlands for about 100 miles. Many of the flows have been folded into anticlines and synclines. Where these folded flows are exposed, the landscape is characterized by prominent ridges formed by the flows. Structural features in the flows include cooling joints (entablature and colonnade), rubble zones, and faults. Many structural features in these flows are similar to structural features in flows that compose most of the Pliocene and younger basaltic-rock aquifers. Open spaces along cooling joints and fractures and in rubble and interflow zones are less common in these flows than in Pliocene and younger basaltic lava flows. In the Miocene basaltic lava flows, some of the open spaces that initially formed during cooling or subsequently formed during folding have been filled with secondary clay minerals, calcite, silica, or unconsolidated alluvial deposits emplaced by streams or in lakes. Except where such fill materials are coarse grained, they tend to decrease markedly the permeability of the Miocene basaltic-rock aquifers.

Pliocene and Younger Volcanic Rocks:20
Pliocene and younger basaltic rocks are present chiefly in the Snake River Plain in Idaho and underlie much of the Cascade Range in Oregon. Pliocene and younger basaltic rocks are chiefly flows but, in many places in the Cascade Range, the rocks contain thick interbeds of basaltic ash, as well as sand and gravel beds deposited by streams. Most of the Pliocene and younger basaltic rocks were extruded as lava flows from numerous vents and fissures concentrated along rift or major fault zones in the Snake River Plain. The lava flows spread for as much as about 50 miles from some vents and fissures. Overlapping shield volcanoes that formed around major vents extruded a complex of basaltic lava flows in some places. Thick soil, much of which is loess, covers the flows in many places. Where exposed at the land surface, the top of a flow typically is undulating and nearly barren of vegetation. The barrenness of such flows contrasts markedly with those covered by thick soil where agricultural development is intensive. The thickness of the individual flows is variable; the thickness of flows of Holocene and Pleistocene age averages about 25 feet, whereas that of Pliocene-age flows averages about 40 feet.

Silicic Volcanic Rocks:20
Silicic volcanic rocks are present chiefly in southwestern Idaho and southeastern Oregon where they consist of thick flows interspersed with unconsolidated deposits of volcanic ash and sand. Silicic volcanic rocks also are the host rock for much of the geothermal water in Idaho and Oregon.


Washington State's Cascade Range Volcanoes

Washington State Volcanoes:14
Washington is home to five major composite volcanoes or stratovolcanoes (from north to south): Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, and Mount Adams. These volcanoes and Mount Hood to the south in Oregon are part of the Cascade Range, a volcanic arc that stretches from southwestern British Columbia to northern California. All Washington volcanoes except Mount Adams have erupted within the last 250 years. However, the volcanoes do not erupt at regular intervals, thus making it difficult to forecast when a given volcano might come to life again. Although worldwide the risks from volcanoes are significantly lower than risks from earthquakes and landslides, the relatively long recurrence interval for volcanic hazards (decades to several centuries) combined with their great potential for destruction make them particularly insidious.
(See Mount Adams, Mount Baker, Glacier Peak, Mount Rainier, and Mount St. Helens below)

Battle Ground Lake

Battle Ground Lake:17
The lake's origin is volcanic, and is believed to have been formed as a "Maar" volcano. This type of volcano is the result of hot lava or magma pushing up near the surface of the earth and then coming into contact with underground water. This is thought to have resulted in a large steam explosion, leaving a crater that later formed a lake. This area was named for a battle that settlers at Fort Vancouver expected to happen in 1855 between U.S. Army soldiers and some Klickitat Indians. The battle never occurred. Captain Strong, the post commander, allowed some Indians to leave the fort on the promise that they would return after burying their chief, who had been accidentally killed. Most fort residents believed a battle would ensue to get the Indians to return, and therefore dubbed the spot "Strong's Battle Ground." The Indians, true to their word, returned peacefully, but the name took hold. Later the area was simply referred to as "Battle Ground."

Beacon Rock

Beacon Rock:17
Beacon Rock is the core of an ancient volcano. The ice-age floods through the Columbia River Gorge eroded the softer material away, leaving this unique geological structure standing by itself on the banks of the Columbia River. Beacon Rock served as a landmark for river travelers for hundreds of years. The Indians knew it marked the last of the rapids on the Columbia River and the beginning of tidal influence from the Pacific Ocean, 150 miles away. Lewis and Clark were the first white men to see the rock. They camped at its base in November of 1805, noting the rock in their journal and giving it its present name. In 1811, Alexander Ross, of the John Jacob Aster expedition, called the rock Inshoack Castle, and it was known as "Castle Rock" until the United States Board of Geographic Names officially restored the title of "Beacon Rock", in 1961. Beacon Rock State Park is located 35 miles east of Vancouver, Washington, on State Route 14, in Skamania County.

Columbia Plateau

Columbia Plateau - Columbia River Gorge7
Between 14 and 16 million years ago, "fissure" volcanic eruptions in eastern Washington, eastern Oregon, and western Idaho produced enormous volumes of molten Columbia River basalt that flowed like water west into the Deschutes-Columbia Plateau province in eastern Washington and northeastern Oregon, with some lava continuing to flow as far west as the Pacific Ocean via the ancestral Columbia River valley. As the basalt cooled and congealed, it formed the columnar cliffs that dominate the landscape today. Erosions by the Columbia River has exposed a particularly spectacular sequence of these rocks in the Columbia River Gorge.

Columbia River Gorge

Columbia River Gorge:8
17-12 million years ago (Miocene) -- During this period, unusual volcanoes, called basalt floods, erupted in eastern Washington and Oregon. These volcanoes were cracks in the earth's crust, several miles long, which poured out floods of liquid molten rock. 41,000 cubic miles (170,000 cubic kilometers) of this lava spread to cover large parts of Oregon and Washington. Out of 270 lava flows that spread across the region, 21 poured through the Gorge forming layers of rock up to 2,000 feet (600 meters) deep.

Drumheller Channels

Drumheller Channels - National Natural Landmark:23
Douglas County - The most spectacular example in the Columbia Plateau Natural Region of "butte-and-basin" scabland, an erosional landscape characterized by hundreds of isolated, steep-sided hills surrounded by a braided network of underfit channels. It represents and illustrates the dramatic modification of the Columbia Plateau volcanic terrain by late Pleistocene catastrophic glacial outburst floods that occurred at a scale remaining unparalleled on earth, either in the geologic record or in historical account. Owner: Federal, State, Private. DESIGNATION DATE: May 1986

Fort Spokane Area

Fort Spokane Area:21
The dark rock that encompasses the Fort Spokane area is basalt. This is hardened lava that came from great fissures on what is now the southern part of the Idaho/Washington border. Beginning approximately 17 million years ago lava flow after lava flow poured onto the landscape of what is now central Washington and northern Oregon. After 11 million years of flows, up to 150 separate lava flows with a combine depth of over 2 miles remain. Most recently wind blown soil, called loess, from the glaciers was deposited on top of the lava flows. Massive floods which roared through central Washington washed away some of this loess. Where the loess remains, the soil is extremely fertile, proving to be excellent for growing wheat, barley, canola and many other crops which you will encounter directly south of Lake Roosevelt. The soil deposits found right along Lake Roosevelt are the result of sediments left from the gigantic Ice Age Floods that came through this area 10,000 to 20,000 years ago.

Ginkgo Petrified Forest

Ginkgo Petrified Forest - National Natural Landmark:23
29 miles east of Ellensburg in Kittitas County. Thousands of logs petrified in lava flows containing an unusually large number of tree species. Logs of the ginkgo tree, rarely found as fossil wood, are located here. Owner: State. DESIGNATION DATE: October 1965

Glacier Peak

Glacier Peak:4,11,18
Glacier Peak (3,213 meters) is a small Cascade Range stratovolcano. Although its summit reaches greater then 3,000 meters above the surrounding valleys, the main cone of Glacier Peak is perched on a high ridge, and the volcanic pile is no more than 500-1,000 meters thick. More than a dozen glaciers occur on the flanks of the volcano, and unconsolidated pyroclastic deposits over 12,000 years old have been largely removed by glaciation. Lava flows locally cap ridges to the northeast of the volcano. While small basaltic flows and cones are found at several points around the flanks of Glacier Peak, the main edifice is largely dacite and andesite. Lava flows extend no more than a few kilometers from the summit. Glacier Peak is probably best known as the source of voluminous tephra eruptions dated to 11,250 years ago. Two tephra layers produced at this time have been identified as far as 800-1,000 kilometers to the east, and are widely used by geologists, anthropologists, and paleoecologists to date late Pleistocene sediments. Also at this time, an extensive valley fill of pumiceous lahars and alluvium was deposited downriver to the west, blocking valleys and affecting drainages as far as 80 kilometers from the volcano. Glacier Peak is not predominantly visible from any major metropolitan centers, and so its attractions, as well as its hazards, tend to be overlooked. Yet, Glacier Peak has produced larger and more explosive eruptions than any other Washington volcano except Mount St. Helens. In the past 14,000 years, Glacier Peak has erupted at least a dozen times, most recently around the eighteenth century. An especially powerful series of eruptions about 13,000 years ago deposited volcanic ash at least as far away as Wyoming.

Goat Rocks Volcanic Field

Goat Rocks:16
The Goat Rocks volcano is a deeply eroded, glaciated volcanic center in an area of wide-spread Pliocene and Pleistocene volcanism along the Cascade crest in southern Washington. Volcanism began approximately 3.2 million years ago with eruption of at least 650 meters of high-silica rhyolite tuff (perhaps a caldera fill), which is exposed on the east flank of the subsequent Goat Rocks volcano. The silicic volcanism ended approximately 3 million years ago, and olivine basalt was locally erupted onto the rhyolitic rocks. Soon thereafter lava flows of high-K2O andesite, dominantly pyroxene phyric but including flows with significant hornblende, formed the Goat Rocks volcano. The volcano was probably build between approximately 2.5 and 0.5 million years ago. Some large volume lava flows moved many kilometers downvalley away from the volcano. The most notable such flow is the 1.0 million-year-old Tieton Andesite, which advanced approximately 80 kilometers eastward down the ancestral Tieton and Naches Rivers, and is the longest known andesite flow on Earth. The Goat Rocks volcano is 70 kilometers west of Yakima and 15 kilometers south of White Pass. Access is by foot along the Pacific Crest trail system from White Pass of several feeder trails east and west of the crest.

Gilbert Peak:16
Gilbert Peak (2,494 meters), the highest point in the area, is capped with hornblende andesite.

Grand Coulee

Grand Coulee:19
Washington has two world-class geologic destinations of stark and eerie beauty that should be on the "must-see" list of any resident. The first, of course, is Mount St. Helens, which is simply the most accessible volcanic, geologic and biological outdoor laboratory on the planet right now. ... The second electrifying feature is Grand Coulee, the basalt canyon that runs south of the dam by the same name. It is the Ice Age bed of the Columbia River. Cliffs remain of an Ice Age waterfall bigger than any in today's world. The coulee is a dramatic reminder of a cyclic flooding that occurred an estimated 40 to 100 times when glacial ice dams repeatedly broke in Western Montana. Each time, about 500 cubic miles of lake water roared across this state in a wall up to 1,000 feet high, at speeds approaching 60 mph, redrawing the surface of the Columbia Plateau. The plateau itself is one of the greatest lava flows on the planet, covering 100,000 square miles.

Grand Coulee:21
Violent events thousands and millions of years ago created the landscape of Coulee Dam and most of eastern Washington. The dark layered rock walls you see as you travel along the lake were built from lava that gushed out of enormous cracks in the earth. Lakeshore sand and gravel terraces are evidence of a more recent event the Ice Age. Prevailing geologic theory suggests that during glaciation, spectacular catastrophic floods raged through this area, carving the canyon of the Grand Coulee and other deep channels.

Grand Coulee - National Natural Landmark:23
Grant County - An illustration of a series of geological events including outpourings of lava, advance and recession of glacial ice, retreat of waterfalls, and the cutting of the Columbia River channel. Owner: Federal, State, Private. DESIGNATION DATE: April 1965

Horsethief State Park

Horsethief Lake State Park:17
Horsethief Lake State Park is a 338-acre camping park with 7,500 feet of freshwater shoreline on the Columbia River. Horsethief Butte dominates the skyline. It stands over the lake like an ancient castle. The lake itself is about 90 acres in size and is actually an impoundment of the Columbia River. The lake was flooded into existence by the reservoir created by The Dalles Dam. For centuries, the park was the site of a Native American village. The Lewis and Clark expedition camped at the village and described its wooden houses in one of their journals. The village was flooded by the waters of The Dalles Dam. Oral history states that the park received its name from workers in the U.S. Army Corps of Engineers who developed the site. The workers thought the terrain was similar to that of horsethief hideouts in popular 1950s Hollywood westerns. The abundance of horses kept on the premises by local Indians apparently gave the workers their inspiration.

Horsethief Butte and Vicinity:17
The Butte and the surrounding Columbia River channel were carved out of basalt rock by floods following the last ice age. The basalt rock resulted from a series of lava flows which emerged from cracks in the earth's crust and blanketed the entire eastern Washington/Oregon region long before the coming of ice-age floods. When viewing the cliffs along the river, notice the stratigraphy highlighted by benches rising up the cliffs. Each of these benches, or layers, represents a different lava flow. Some lava flows were hundreds of feet thick in places.

Kamiak Butte

Kamiak Butte - National Natural Landmark:23
Whitman County - Isolated mountain peaks of older rock surrounded by basalt, rising above the surrounding lava plateau. Part of outliers of Couer d' Alene Mountains of Idaho. Owner: State, County, Private. DESIGNATION DATE: April 1980

Lyons Ferry State Park

Lyons Ferry State Park:17
The rich geologic history of this 1,282-acre park is readily evidenced by basaltic formations that outline the paths of both the Snake and the Palouse rivers. Park visitors drive through rolling hills of agricultural land, broken lava, dry grass and sagebrush for opportunities to wander through what geologists call "the strangest landscape this side of Mars." These "Channeled Scablands" are part of hundreds of square miles of raw, peeled ground that stretch from Spokane west to the Cascades and south to the Snake River.

Mount Adams

Mount Adams:1,10,18
Mount Adams (3,742 meters) stands astride the Cascade Crest some 50 kilometers due east of Mount St. Helens. The towering stratovolcano is marked by a dozen glaciers, most of which are fed radially from its summit icecap. Mount Adams is composed of lava flows and fragmental rocks of basaltic andesite and andesite; numerous satellitic vents on the flanks of the volcano have erupted rocks ranging from basalt to dacite. Most of the main cone is younger than 220,000 years. Mount Adams has produced few eruptions during the past several thousand years. This volcano's most recent activity was a series of small eruptions about 1,000 years ago.

Mount Baker

Mount Baker:3,9,18
Mount Baker (3,285 meters) is the northernmost and most isolated of the Cascade volcanoes in the USA. The andesitic cone rises nearly 2 kilometers above the older metamorphic and sedimentary rocks at its base and it is almost completely covered in glaciers -- hence its original Nooksack Indian name "White Steep Mountain". Mount Baker is a large stratovolcano in northwestern Washington about 30 kilometers east of Bellingham and 25 kilometers south of the International Boundary. The present cone was formed prior to the last major glaciation, which occurred between about 25,000 and 10,000 years ago, and probably is considerably older. The cone overlaps rocks of an earlier eruptive center from which two radiometric dates of about 400,000 years have been obtained. Mount Baker erupted in the mid-1800's for the first time in several thousand years. Activity at steam vents (fumaroles) in Sherman Crater, near the volcano's summit, increased in 1975 and is still vigorous, but there is no evidence that an eruption is imminent.

Mount Rainier -
Mount Rainier National Park

Mount Rainier:13
Mount Rainier is an active volcano that first erupted about half a million years ago. Because of Rainier's great height (14,410 feet above sea level) and northerly location, glaciers have cut deeply into its lavas, making it appear deceptively older than it actually is. Mount Rainier is known to have erupted as recently as in the 1840s, and large eruptions took place as recently as about 1,000 and 2,300 years ago. Mount Rainier and other similar volcanoes in the Cascade Range, such as Mount Adams and Mount Baker, erupt much less frequently than the more familiar Hawaiian volcanoes, but their eruptions are vastly more destructive. Hot lava and rock debris from Rainier's eruptions have melted snow and glacier ice and triggered debris flows (mudflows) - with a consistency of churning wet concrete - that have swept down all of the river valleys that head on the volcano. Debris flows have also formed by collapse of unstable parts of the volcano without accompanying eruptions. Some debris flows have traveled as far as the present margin of Puget Sound, and much of the lowland to the east of Tacoma and the south of Seattle is formed of pre-historic debris from Mount Rainier.

Mount Spokane

Mount Spokane:14
Mount Spokane consists of foliated Cretaceous two-mica granite that intruded Precambrian paragneiss (high-temperature metamorphosed sedimentary rocks).

Mount Spokane State Park:17
Mount Spokane State Park is a 13,919-acre camping park in the Selkirk Mountains. The view at the top of the 5,883-foot elevation includes surrounding states and Canada. The forested park features stands of old-growth timber and granite rock outcroppings. In winter, the park receives 300 inches of snow.

Mount St. Helens -
Mount St. Helens National Volcanic Monument

Mount St. Helens:18
Mount St. Helens is the most frequently active volcano in the Cascades. During the past 4,000 years, it has produced many lahars and a wide variety of eruptive activity, from relatively quiet outflows of lava to explosive eruptions much larger than that of May 18, 1980.

North Cascades -
North Cascades National Park

North Cascades:5
The North Cascades are still rising, shifting, and forming. Geologists believe that these mountains are a collage of terranes, distinct assemblages of rock separated by faults. Fossil and rock magnetism studies indicate that the North Cascades Terranes were formed in other places, some many thousands of miles south of here. Attached to slowly moving plates of oceanic rock, they drifted northward, merging together about 90 million years ago. Exactly when they arrived here is still in question. Colliding with the North American Continent, the drifting rock masses were thrust upwards and faulted laterally into a jumbled array of mountains. The collision broke or sliced the terrane into north to south trending faults that are still evident today. Highway 20 crosses the Straight Creek fault just east of Marblemount. Geologists believe the rocks to the west of the fault slid more than 100 miles north of the slice to the east. The rocks to the east of Straight Creek Fault are gneisses and granites, while those to the west are completely different recrystallized mudstones and sandstones. Over time, these predecessors to today's North Cascades were further faulted and eroded to a nearly level plain. During the past 40 million years, heavier oceanic rocks thrust beneath the edge of this region. Intense heat at great depths caused them to melt. Some of the melt rose to the surface in fiery volcanic eruptions like Mount Baker. The rest crystallized at various depths to form vast bodies of granitic rock. The North Cascades have again pushed upward to majestic heights, exposing the roots of the ancient collision zone. Ice, water, and wind will eventually level the peaks around us, returning them bit by bit to the sea.

Big Bosom Buttes:15
Big Bosom Buttes reveal the remains of a volcanic caldera that erupted about 25-30 million years ago (Oligocene), during the early years of the Cascade Volcanic Arc.

Hannegan Pass:15
The defile of Hannegan Pass is not very volcanolike, but the pass, in fact, has been eroded from the volcanic filling of ancient Hannegan Caldera. The eroded slopes all around are deposits of volcanic ash and breccia deposits that erupted some 4 million years ago and filled a hole in the land created by the collapse of the roof of an emptying magma chamber.

Table Mountain and Kulshan Caldera:15
Under the dark lavas of Table Mountain, and forming white cliffs above Swift Creek, are the older volcanic deposits of Kulshan Caldera. The edge of this large volcanic depression is more or less directly beneath the parking area. The caldera is, about 2.5 miles across. If formed and was filled with volcanic tuff (the rock formed from volcanic ash) about 1.1 million years ago, when the magma chamber beneath it erupted, and its roof collapsed. Volcanologists have identified ash deposits from the Kulshan volcanic eruption as far away as southern Puget Sound.

Olympic Mountains -
Olympic National Park

Olympic Mountains:6
Consider the Olympic Mountains to be an ancient sea floor that has been wedged into the North American Continent and uplifted into the atmosphere by surrounding geologic pressures. As the topmost layer of the sea floor is scraped off and crumpled on to the North American Plate, the lower branch dives beneath Olympic creating heat and pressure that eventually form the volcanoes of the Cascades. The Olympic Mountains are not very high -- Mount Olympus, the highest, is just under 8,000 feet -- but they rise almost from the water's edge and intercept moisture-rich air masses that move in from the Pacific. As this air is forced over the mountains, it cools and releases moisture in the form of rain or snow. At lower elevations rain nurtures the forests while at higher elevations snow adds to glacial masses that relentlessly carve the landscape. The mountains wring precipitation out of the air so effectively that areas on the northeast corner of the peninsula experience a rain shadow and get very little rain. The town of Sequim gets only 17 inches a year, while less than 30 miles away Mount Olympus receives over 220 inches falling mostly as snow. There are about 266 glaciers crowning the Olympics peaks; most of them are quite small in contrast to the great rivers of ice in Alaska. The prominent glaciers are those on Mount Olympus covering approximately ten square miles. Beyond the Olympic complex are the glaciers of Mount Carrie, the Bailey Range, Mount Christie, and Mount Anderson.

Olympic Mountains Formation:6
These mountains have arisen from the sea. For eons, wind and rain washed sediments from the land into the ocean. Over time these sediments were compressed into shale and sandstone. Meanwhile, vents and fissures opened under the water and lava flowed forth, creating huge underwater mountains and ranges called seamounts. The plate(s) that formed the ocean floor inched toward North America about 35 million years ago and most of the sea floor went beneath the continental land mass. Some of the sea floor, however, was scraped off and jammed against the mainland, creating the dome that was the forerunner of today's Olympics. Powerful forces fractured, folded, and over-turned rock formations, which helps explain the jumbled appearance of the Olympics. Radiating out from the center of the dome, streams, and later a series of glaciers, carved peaks and valleys, creating the beautiful, craggy landscape we know today. Ice Age glacial sheets from the north carved out the Strait of Juan Fuca and Puget Sound, isolating the Olympics from nearby landmasses.

Potholes State Park

Potholes State Park:17
The park is located in the area of the West known as "the Scablands." The terrain was formed by large lava flows, followed by huge floods (known as Missoula floods) and winds. Large sand dunes, coulees and lava flows can be visited near the park.

Steamboat Rock State Park

Steamboat Rock:17
Steamboat Rock State Park is a 3,522-acre camping park with 50,000 feet of freshwater shoreline at the north end of Banks Lake. Dominating the landscape is a columnar, basaltic rock with a surface area of 600 acres. Two campground areas and a large day-use area are on sweeping green lawns, protected from winds by tall dramatic poplars. The surrounding areas are carpeted with wildflowers, adding to the gray-green brush of the Scablands. A sandy swimming area and boat launches make the area a favorite for visitors who enjoy water-play and want respite from the hot, summer sun. Steamboat Rock is a long-established area landmark, first used by nomadic Native American tribes and then by early settlers. The military currently uses the area for aircraft flying training missions. The basalt butte rises 800 feet above Banks Lake. It was once an island in the Columbia River bed. When the Columbia returned to its natural course, after centuries of being dammed by ice, the massive rock remained.

Steptoe Butte State Park

Steptoe Butte:22
Steptoe Butte is the type example of a steptoe, an isolated hill or mountain surrounded by lava flows.

Steptoe Butte State Park:17
Steptoe Butte State Park is a 150-acre, 3,612-foot-tall natural monument. Thimble-shaped, the granite butte looms in bald grandeur over the prevailing flat lands.

Steptoe Butte - National Natural Landmark:23
Whitman County - Isolated mountain peaks of older rock surrounded by basalt, rising above the surrounding lava plateau. Part of outliers of Couer d' Alene Mountains of Idaho. Owner: State, County, Private. DESIGNATION DATE: October 1965

Underwood Mountain

Underwood Mountain:24
A shield volcano.

Wallula Gap

Wallula Gap - National Natural Landmark:23
Mainly located in Benton County and extends into Walla Walla County - The largest, most spectacular, and most significant of the several large water gaps through basalt anticlines in the Columbia River basin. Owner: Federal, Municipal, Private. DESIGNATION DATE: August 1980

Wind Mountain

Wind Mountain:24
A quartz diorite intrusion. The Wind Mountain intrusion is a fine-grained plagioclase-phyric quartz diorite, in places with hypersthene and hornblende phenocrysts. The intrusion contains inclusions of Grande Ronde Basalt, and basalt on the west side of Dog Mountain, 3 kilometers farther east (Columbia River Gorge) was hornfelsed by the intrusion. A similar quartz diorite occurs south of the Columbia River at Shellrock Mountain. These shallow bodies, and several others in the area, presumably were related to volcanic activity. K-Ar whole-rock ages of 4.9 +/- 0.1 million years and 6.6 +/- 0.7 million years have been obtained for the Wind Mountain intrusion.

Excerpts from:
1) Hoblitt,, 1987, USGS Open-File Report 87-297
2) Hoblitt,, 1995, USGS Open-File Report 95-273
3) Hyde and Crandell, 1978, USGS Professional Paper 1022-C
4) Mastin and Waitt, 1995, USGS Open-File Report 95-413
5) U.S. National Park Service Website, North Cascades National Park, 2001
6) U.S. National Park Service Website, Olympic National Park, 2000
7) Geologic Sightseeing: Oregon Department of Geology and Mineral Resources Website, 2001
8) U.S. Army Corps of Engineers, Portland District, and the U. S. Department of the Interior, U. S. Geological Survey, The Geologic History of the Columbia River Gorge: Information Brochure
9) Wood, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press
10) Hildreth, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press
11) Beget, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press
12) Crandell, 1971, Postglacial Lahars From Mount Rainier Volcano, Washington: USGS Professional Paper 677
13) Sisson, 1995, History and Hazards of Mount Rainier, Washington: USGS Open-File Report 95-642
14)Washington State Department of Natural Resources Website, 2001, 2002
15) USGS/NPS Geology in the Parks Website, 2001
16) Swanson, 1990, IN: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press
17) Washington State Parks Website, 2000, 2002
18) Dzurisin,, 1997, Living With Volcanic Risk in the Cascades: USGS Fact Sheet 165-97
19) USGS Earthquake Hazards Program, Pacific Northwest Website, 2002
20) Whitehead, R.L., 1994, Ground Water Atlas of the United States: Idaho, Oregon, Washington: U.S. Geological Survey HA730-H
21) U.S. National Park Service, Lake Roosevelt National Recreation Area Website, 2002
22) U.S. National Park Service, Columbia Cascades Cluster Website, 2002
23) U.S. National Park Service, National Natural Landmarks Website, 2003
24) Swanson, D.A.,, 1989, IGC Field Trip T106: Cenozoic Volcanism in the Cascade Range and Columbia Plateau, Southern Washington and Northernmost Oregon: American Geophysical Union Field Trip Guidebook T106, p.21-24.

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06/11/03, Lyn Topinka