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Stratigraphy Theme Key
Rock Properties Theme Key
Basic Rock Type Theme Key
Faults Overlay Key

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Stratigraphy Theme Key

The map based on the following stratigraphic map units is only one way to display geologic data contained within the database. Map units are broadly defined and include many different units that could be displayed individually or grouped under different selection criteria. For this particular map, Columbia River Basalt Group units have been de-emphasized to highlight the patterns of volcanism that followed eruption of the Columbia River Basalt lavas. Note that the unit color depends on the scale: when zoomed in to at least 1:750,000 (when the basemaps can be displayed), the color is semi-transparent to allow basemap information to be visible. When viewing the map, be sure to use the Info Query tool to display more detailed stratigraphic information, including the reference map ID, which provides the original source for the data.

Color	Stratigraphic Unit
	Quaternary surficial deposits – Mostly alluvium, colluvium, and landslide deposits that have formed over the last 1.8 million years. Includes terrace, glacial, and eolian deposits and outburst flood deposits left by the Missoula and Bonneville floods.
	Neogene sedimentary rocks - Mostly late Miocene and Pliocene (11.2 million to 1.8 million years old) tuffaceous sedimentary rocks deposited in ancient streams and lakes. Includes the Mascall, Rattlesnake, Drewsey, Trout Creek and Bully Creek Formations.
	Dalles Group – Late Miocene and Pliocene (11.2 million to 1.8 million years old) sedimentary rocks interbedded with Saddle Mountains Basalt flows near Pendleton. Includes the McKay and Alkali Canyon Formations.
	Idaho Group - Late Miocene and Pliocene (11.2 million to 1.8 million years old) continental sedimentary rocks associated with the large lacustrine systems of western Idaho. Includes the Glenns Ferry Formation.
	Paleogene sedimentary rocks – Paleocene to Oligocene (66.5 to 23.7 million years old) Arkosic sandstone, siltstone, and cobble gravel deposited by ancient rivers and lakes. Includes all Tertiary continental sedimentary rocks that were deposited before the onset of continental margin volcanism. Includes the Herren Formation.
	Late High Cascade Volcanics – Quaternary (1.8 million years to a few thousand years old) lava flows, cinder cones, and stratovolcanoes along the axis of the high Cascade Range. Predominantly basalt and basaltic andesite flows, with minor andesite and dacite flows and volcaniclastic rocks and deposits.
	Quaternary volcanic rocks – Basalt and basaltic andesite lava flows and vent deposits that are Quaternary (less than 1.8 million years old) in age. Includes the Jordan Craters, Saddle Butte, and Diamond Craters lava fields.
	Kivett Volcanics - Late Pliocene and early Pleistocene lava flows and vent deposits. Includes olivine basalt, alkali basalt, and trachyandesite flows that overlie Idaho Group and related sedimentary deposits.
	Early High Cascade Volcanics – Pliocene (5.3 to 1.8 million years old) volcanic rocks that overlie the Western Cascades and are in turn overlain by the Late High Cascades rocks. Predominantly basalt, andesite, and dacite flows, with minor volcaniclastic rocks.
	Neogene volcanic rocks – Disparate series of Miocene to Pliocene (23.8 to 1.8 million years old) basalt, andesite, dacite, rhyolite, and olivine basalt lava flows that erupted from scattered vents following the eruption of the last large rhyolite ash-flows associated with the Lake Owyhee, McDermitt, and Northern Nevada volcanic fields. In some places, such as northern Malheur county, probably includes lava flows that, with more detailed mapping, could be included in the Columbia River Basalt Group. Includes the Jump Creek Rhyolite and Plush and Swisher Mountain tuffs.
	Harney Basin Volcanic Field – Series of rhyolite lava flows, and ash-flow tuffs, that erupted in the late Miocene from calderas and rhyolite eruptive centers centered on Burns, Oregon. Ages of major ash-flows, including the Rattlesnake, Devine Canyon, and Prater Creek range from about 7.5 million years ago to 10 million years ago. Includes associated tuffaceous sedimentary rocks.
	High Lava Plains Volcanic Province – Series of Late Miocene and Pliocene (11.2 million to 1.8 million year old) olivine basalt and andesite lava flows that erupted from vents in the northern Basin and Range Province.
	Powder River Volcanic Field – Series of Middle Miocene and Pliocene (16.4 million to 1.8 million years old) andesite, dacite, olivine basalt, and basanite lava flows that erupted from a number of small volcanoes that were located between La Grande and Baker City. Earliest eruptions are olivine basalt flows that overlie ash-flows erupted from the Lake Owyhee Volcanic Field.
	Strawberry Volcanics - Series of Miocene (23.8 to 5.3 million years old) andesite, dacite, and olivine basalt lava flows that erupted from a number of composite volcanoes near John Day. Extent, stratigraphy and contact relationships with adjoining units remain to be fully determined.
	Columbia River Basalt Group - Most widespread geologic unit in the Pacific Northwest including all mafic lava flows of middle Miocene age that erupted between about 17 million years ago and 15 million years ago. Major formations include the Imnaha Basalt, Steens Basalt, Picture Gorge Basalt, Grande Ronde Basalt, Wanapum Basalt, and Saddle Mountains Basalt. Although mostly basalt or basaltic andesite lava flows, locally includes, in the south central part of the exposure belt, rhyolitic ash-flow tuff and tuffaceous sedimentary rocks. In the north central part of the exposure belt, includes Saddle Mountains Basalt flows as young as 6 million years.
	Lake Owyhee Volcanic Field – Miocene (23.8 to 5.3 million years old) rhyolite lava flows, ash-flow tuffs, and tuffaceous sedimentary rocks that erupted from calderas and rhyolite eruptive centers extending north from the Mahogany Mountain caldera in extreme eastern Oregon to the Dooley Mountain complex south of Baker City. Notable units include the Dinner Creek Wildcat Creek and Leslie Gulch ash-flow tuff, and the Littlefield Rhyolite. Earliest ash-flow is interbedded with Columbia River Basalt Group lava flows.
	Oregon–Idaho Graben – Series of Miocene (23.8 to 5.3 million years old) intricately interbedded olivine basalt, andesite, and dacite lava flows; small ash-flow tuffs, mafic hydrovolcanic deposits, tuffaceous sedimentary rocks, and arkosic sandstone and conglomerate. Includes middle and late Miocene units that unconformably overlie Lake Owyhee Volcanic Field rhyolites.
	McDermitt Volcanic Field – Miocene (23.8 to 5.3 million years old) rhyolite lava flows, ash-flow tuffs, and tuffaceous sedimentary rocks associated with the McDermitt and Whitehorse calderas in extreme southeast Oregon. Notable ash-flows include the tuffs of Oregon Canyon, Long Ridge, Trout Creek Mountains and Whitehorse Creek. Earliest ash-flows are interbedded with Columbia River Basalt Group lava flows.
	Northern Nevada volcanics – Miocene (23.8 to 5.3 million years old) rhyolite lava flows, ash-flow tuffs, and tuffaceous sedimentary rocks that erupted from calderas and rhyolite eruptive centers in northwest Nevada. Age relationships not precisely defined, but includes large Miocene ash-flows that overlie Steens Basalt lava flows.
	John Day-Clarno Group – Eocene to Oligocene (54.8 to 23.8 million years old) Lava flows, ash-flows, mudflow breccia deposits, volcaniclastic sedimentary rocks, and subvolcanic intrusions. Includes John Day and Clarno Formations. Encompasses all Tertiary volcanic rocks that underlie Columbia River Basalt Group units in the Blue Mountains geomorphic province.
	Western Cascades Volcanics – Eocene to Miocene (54.8 to 5.3 million years old) volcanic and volcaniclastic rocks that underlie much of the west slope of the Cascade Range. Includes numerous large ash flow sheets, and the Little Butte Volcanics, Scorpion Mountain volcanics, and Sardine formation.
	Paleogene volcanic rocks – Eocene to Oligocene (57.8 to 23.8 million years old) lava flows, ash-flows, mudflow breccia deposits, volcaniclastic sedimentary rocks, and subvolcanic intrusions. Encompasses all Tertiary volcanic rocks that formed before onset of Columbia River Basalt volcanism in the Basin and Range geomorphic province. Includes the Alvord and Pike Creek formations and the Steens Mountain and Warner Peak volcanics.
	Umpqua Group – Paleocene to Early Eocene (65 to 49 million years old) marine sandstone, conglomerate, shale, and siltstone located mainly in western Oregon. Includes the White Tail Ridge, Tenmile, Bushnell Rock, and Camas Formations.
	Nevadan Intrusives - Mainly tonalite, granodiorite, and granite intrusive complexes that were emplaced during the Nevadan Orogeny, during the late Jurassic and early Cretaceous (259 to 99 million years old). Includes the Bald Mountain and Wallowa batholiths.
	Pueblo Mountain Metamorphic Complex - Mainly Jurassic (206 to 144 million years old) greenstone, phyllite, and chlorite-mica schists. Exposed in the extreme southern part of eastern Oregon, south of Fields.
	Mountain Home Metamorphic Complex – Mainly chlorite and garnet-mica schists exposed near Pendleton that cannot be assigned to any of the northeast Oregon accreted terranes with any degree of certainty. Higher grade metamorphic rocks contain sillimanite and staurolite, age is Paleozoic to Mesozoic (543 to 65 million years old).
	Mitchell Group – Marine sandstone, siltstone, and conglomerate. Includes all Cretaceous (144 to 65 million years old) sedimentary rocks that were deposited after emplacement of early Cretaceous plutons.
	Wallowa Terrane – Island arc volcanic and shallow marine deposits associated with the northernmost of the northeast Oregon accreted terranes. Mainly Permian and Triassic (290 to 206 million years old) in age and includes the Martin Bridge, Hurwal, and Clover Creek formations. Subvolcanic intrusive complexes include the Sparta Complex.
	Baker Terrane – Complexly deformed assemblage of deep ocean floor, island arc, and mélange deposits associated with the central northeast Oregon accreted terrane. Includes rocks of Pennsylvanian, Permian, and Triassic age (323 to 206 million years old). Major formations include the Elkhorn Ridge Argillite and Burnt River Schist.
	Olds Ferry Terrane – Island arc volcanic and associated fore-arc marine deposits associated with the southernmost northeast Oregon terranes. Mainly Triassic and Jurassic (290 to 144 million years old) in age. Major units include the Weatherby, Vester, Fields Creek, and Huntington Formations.
	Grindstone Terrane – Complexly deformed assemblage of deep and shallow water marine and continental deposits associated with the westernmost of the northeast Oregon accreted terranes. Includes rocks of Devonian, Mississippian, Pennsylvanian, Permian, Triassic, and Jurassic age (417 to 65 million years old).
	Info Query popup fields: Terrane Group Formation Member Unit Reference ID

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Rock Properties Theme Key

The Rock Properties theme map shows rock types based on genesis, which can influence grain size, layering, and other geotechnical properties. In addition, the "unit" is a function of how the original author described the lithology; particularly for "metamorphic" vs. "metamorphosed" terms, the original author's usage is retained. A slash (/) between rock types indicates that the "unit" is made of all the rock types listed for the unit. Note that the unit color depends on the scale: when zoomed in to at least 1:750,000 (when the basemaps can be displayed), the color is semi-transparent to allow basemap information to be visible. When viewing the map, be sure to use the Info Query tool to display the geotechnical properties.

Color	Rock Property Lithology Unit
	Intrusive rocks – Formed by the intrusion of magma into pre-existing rocks below the Earth’s surface. When the magma cools deep in the crust, it forms rocks made of interlocking mineral crystals. In this application the term includes only the smaller sizes of intruded rock bodies, like dikes, sills, and stocks.
	Intrusive/metamorphic rocks – A mixed unit of two kinds of rocks formed by the intrusion of magma into the Earth’s crust and by the changes/melting that the magma’s heat makes on the rocks surrounding the intrusion. The melting is not complete everywhere, so many of the rocks are partly intrusive and partly metamorphic.
	Intrusive/plutonic rocks – A mixed unit of two kinds of rocks formed by the intrusion of magma into the Earth’s crust. The plutonic rocks form when a large magma pool cools below the Earth’s surface. The intrusive rocks are the result of the magma’s leakage into cracks in the rocks surrounding the large magma body.
	Intrusive/sedimentary/volcanic rocks – A unit generally found only on small scale (1:100,000 and greater) maps because the scale is too small to show each kind of rock separately. The rocks may be related through being deposited in one place, but they generally have different origins. For example, the products of a volcano that erupts into the ocean may include a central eruption vent (intrusive) and (volcanic) flows and fragments that are then sorted and rounded by the waves into shoreline (sedimentary) rocks that surround the volcano.
	Intrusive/volcanic rocks – A mixed unit of two kinds of rocks formed by the intrusion of magma into cracks in the Earth’s crust and eruption of this magma onto the Earth’s surface. The intrusive rocks form from the cooling of the leftover magma remaining in the crust’s cracks after most of it has pushed to the surface and then erupted to form the volcanic rocks.
	Lava flows – Formed when molten magma flows onto the Earth’s surface as it is erupted as lava. The resulting rocks can have many different characteristics, depending upon the magma/lava’s chemical composition and gas content, and on its interactions as it erupts with lake and stream water.
	Metamorphic rocks – Formed by chemical and crystal changes produced by the actions of temperature, pressure, and stress on pre-existing rocks deep within the Earth’s crust. The amount of change can range from only the slight formation of a few new mineral crystals in the old rock to forming completely recrystallized rocks. Common metamorphic rocks are quartzite, marble, and mica schist.
	Metamorphic/plutonic rocks – A mixed unit of two kinds of rocks formed by the intrusion of magma into the Earth’s crust and by the change that the magma’s heat makes on the pre-existing rocks surrounding the magma pool. Many of these rocks are vary back and forth from one type of rock to another, changing from the coarse interlocking crystals of the plutonic rocks to the layers of mica minerals in the metamorphic rocks.
	Metamorphic/sedimentary/volcanic rocks – A unit generally found only on small scale (1:100,000 and larger) maps because the scale is too small to show each kind of rock separately. The rocks may have the same origin, as in pre-existing sedimentary and volcanic sandstones that have been partially or completely changed and recrystallized by the heat of a nearby magma chamber.
	Metamorphic/volcanic rocks – A mixture of two kinds of rocks that were first erupted from a volcano. Then parts of the volcanic lava flows were changed by the heat and pressure of being buried deep in the Earth’s crust, or by the heat from a nearby pool of magma. For example, parts of the volcanic lava flows in an area may have been changed into metamorphic "greenstones."
	Metamorphosed intrusive rocks – Intrusive rocks that have retained most of their original crystalline character, but have been subtly changed by heat and pressure. Some geologists also like to map only the original rock types of a metamorphic terrain, like mapping a metamorphosed basalt dike, even if the present exposed rock is a metamorphic greenstone.
	Metamorphosed intrusive/plutonic rocks – Related intrusive and plutonic rocks that have retained most of their original crystalline character, but have been subtly changed by heat and pressure. Some geologists also like to map only the original rock types of a metamorphic terrain, like mapping a metamorphosed granite pluton and dikes, even if the present exposed rocks are all metamorphic gneisses.
	Metamorphosed plutonic rocks – Plutonic rocks that have retained most of their original coarsely crystalline character, but have been subtly changed by heat and pressure. Some geologists also like to map only the original rock types of a metamorphic terrain, like mapping a metamorphosed basalt dike, even if the present rock is a metamorphic greenstone.
	Metamorphosed plutonic/sedimentary/volcanic rocks – A unit generally found only on small scale (1:100,000 and larger) maps because the scale is too small to portray each rock type separately. The rocks have retained most of the original characteristics of that rock type, but have been subtly changed by the heat and pressure of metamorphic processes.
	Metamorphosed plutonic/volcanic rocks – Possibly related plutonic and volcanic rocks that have retained most of their original crystal and other characteristics, but have been subtly changed by heat and pressure. Some geologists also like to map only the original rock types of a metamorphic terrain, like mapping a metamorphosed granite pluton and its related rhyolite volcanics, even if the present exposed rocks are all metamorphic gneisses.
	Metamorphosed sedimentary rocks – Sedimentary rocks that have retained most of their layered and fragmental character, but have been subtly changed by heat and pressure—mudstone to phyllite. Some geologists also like to map only the original rock types of a metamorphic terrain, like mapping a metamorphosed limestone, even if the present exposed rock is all marble.
	Metamorphosed sedimentary/volcanic rocks – Possibly related sedimentary and volcanic rocks that have retained most of their original layering, flow shapes, and other characteristics, but that have been subtly changed by heat and pressure. Some geologists also like to map only the original rock types of a metamorphic terrain, like mapping a unit of greenstone and argillite as a metamorphosed basalt flow and its possibly related interlayered mudstone.
	Metamorphosed volcanic rocks – Volcanic rocks that have retained most of their finely crystalline lava flow and/or fragmental characteristics, but have been subtly changed by heat and pressure. Some geologists also like to map only the original rock types of a metamorphic terrain, like mapping a metamorphosed basalt lava flow, even if the present rock is a greenstone.
	Plutonic rocks – Formed by the intrusion of very large pools of magma into the pre-existing rock below the Earth’s surface. When the magma cools deep in the crust it forms large bodies of rocks made of interlocking coarse mineral crystals. In this application the term includes plutons and batholiths that can cover many miles of an area, like the Ashland Pluton in southern Oregon and the Wallowa Batholith in the mountains of eastern Oregon.
	Sediments – Weathered and eroded rock fragments have been transported by air, wind, ice, or landslides and deposited within lakes, stream valleys, deserts, and under glacial ice at some time in the past. In this context these rocks are generally only slightly consolidated, compacted and cemented, like sand, gravel, silt, mud, glacial till, sand dunes, etc. However, they are also no longer associated with the process that originally caused them to be moved and deposited. The sediment grains are generally somewhat rounded and sorted, and range in size from clay to boulders.
	Sedimentary rocks – Rock resulting from the consolidation and cementation of loose sediments, and generally found in layers. The sediments are formed by the transportation and deposition of weathered rock fragments by Earth’s surface processes like streams, landslides, marine tides, etc. The sedimentary rocks are no longer associated with the processes that originally deposited them. They can also be the result of the precipitation of minerals like lime and phosphate by super-concentrated water solutions or in the shells and bones of animals. Common sedimentary rocks are limestone, sandstone, conglomerate, and chert.
	Sedimentary/volcanic rocks – A mixed unit of two kinds of rocks formed when some of the products of a volcanic eruption are weathered, eroded, and changed by the actions of water, ice, wind, or other processes happening on the Earth’s surface. On the islands of Hawaii the ocean waves are eroding the lava flows of the Hawaiian volcanoes, creating nearby black volcanic sand beaches under the cliffs of the lava flows.
	Ultramafic/volcanic rocks – A mixed unit of two kinds of rocks typically formed in the deep ocean at spreading volcanic ridges. Later all the rocks are brought to the Earth’s surface by the collision of the Earth’s continental and oceanic plates. The lava flows that erupted onto the ocean floor are often found today with their ancient "plumbing systems" - the ultramafic intrusive rocks formed beneath the spreading ridges from the same magma that erupted as the volcanoes.
	Ultramafic rocks – The most exotic of the Earth’s rocks, these were formed deep within the Earth’s crust, or as volcanic rocks formed in the deep ocean at volcanic spreading ridges. They are then exposed on the surface through the actions of mountain-building collision of the Earth’s continental and oceanic plates. Generally these rocks are made of only one kind of mineral, which contain high amounts of iron and magnesium elements, like olivine, pyroxene and hornblende.
	Unconsolidated rocks – Weathered and eroded rock fragments that have been transported by air, wind, ice, landslides, and other weather processes of the Earth’s surface. The fragments are presently being deposited within lakes, stream valleys, deserts, and under glacial ice. These rocks are not consolidated, compacted or cemented, and examples are ocean beach sand, alluvial fan gravel, lake silt, glacial till, and swamp mud. The sediment grains are generally at least somewhat rounded and sorted, and range in size from clay to boulders.
	Volcanic rocks – Any product of a volcanic eruption. The resulting rocks can have many different characteristics, depending upon the magma’s original chemical composition and gas content, and on its interaction as it erupts with the water of lakes and streams. These rock units include both lava flows and fragmental rocks. Generally the crystals in these rocks are made of fine interlocking mineral crystals or are glassy, but many of them also contain larger crystals that appear to “float” in the glassy background, and are visible to the naked eye.
	Volcaniclastic rocks – Fragmental rocks formed during a volcanic eruption. The fragments are mainly formed by the force of the volcanic eruption, but some are formed when the volcano’s lava flows interact with water. They are deposited after flying through the air, as in the droplets formed by fountains of lava, or the ash deposits formed when clouds of ash rush down the sides of the volcano. The volcanic rock pieces can range in size from fine ash to house-sized boulders.
	Info Query popup fields: Lithology General Unit Lithology Rock Type Crystal/Grain Size Layering Geotech Properties Reference ID

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Basic Rock Type Theme Key

The Basic Rock Type theme map shows rock types in the most general terms. Note that the unit color depends on the scale: when zoomed in to at least 1:750,000 (when the basemaps can be displayed), the color is semi-transparent to allow basemap information to be visible. When viewing the map, be sure to use the Info Query tool to display more detailed information.

Color	Basic Rock Type
	metamorphic - Formed by the chemical, mineralogical, and structural changes produced on rocks by the actions of temperature, pressure, and stress on pre-existing rocks deep within the Earth’s crust. Metamorphic rocks can also be the result of magma heating the surrounding rocks as it moves up to the Earth’s surface, or by the pressure put on pre-existing rocks when they are deeply buried by younger sediments in basins. The amount of change ranges from only a little change in the original rocks, which retain most of their original characteristics, to completely recrystallized rocks, formed by the cooling of nearly melted rocks. Common metamorphic rock types are: mica schist, gneiss, quartzite, and marble. Both the Klamath Mountains of southwestern Oregon and the Wallowa Mountains of northeastern Oregon contain large areas of metamorphic rocks.
	plutonic – Formed by magma’s intrusion below the Earth’s surface into pre-existing rocks. When large pools of magma slowly cool deep in the crust, they form miles-wide bodies of rocks made of interlocking coarse crystals, commonly called plutons and batholiths, depending on their size. When the magma moves up into the upper part of the crust, on the way to erupting on the surface as a volcano, it forms smaller intrusions, which can range in width from inches to tens of feet. The resulting more plutonic rocks, called dikes and sill, are made up of finer interlocking crystals, and cut across the layers of the pre-existing rocks. Oregon has many examples of plutonic rocks, like the Ashland Pluton in southern Oregon and the Wallowa Batholith forming eastern Oregon’s Wallowa Mountains.
	sedimentary – Rock formed by the consolidation and/or cementation of loose eroded sediments. Generally found in layers, the sedimentary rocks are formed by the transportation and deposition of rock fragments eroded by water, wind, and gravity processes on the Earth’s surface, like streams, landslides, marine tides, etc. They can also be the result of the precipitation of minerals like lime and phosphate by super-concentrated water solutions or in the shells and bones of animals. However, the sedimentary rocks are no longer associated with the processes that originally deposited them. Common sedimentary rocks are limestone, sandstone, and conglomerate. In many areas of Oregon the sedimentary rocks are covered by rocks shed by the volcanic rocks that are up at the tops of cliffs. Sedimentary rock examples are the 45-50 million-year-old sediments that formed deep in the ocean basins and are now uplifted in parts of the Coast Range of western Oregon and the 190 million-year-old limestone and marble of the Oregon Caves National Monument in southern Oregon.
	surficial sediments – Result from the transport and deposit of weathered and eroded rock fragments by air, wind, ice, gravity and other processes of the Earth’s surface. The fragments are presently being deposited within our state’s lakes, stream valleys, deserts, and under glacial ice. The sediment grains are generally rounded and sorted to some extent, and range in particle size from clay to boulders. These rocks are poorly consolidated, compacted, or cemented, if at all. Examples in Oregon include the sands of the Newport beach sand dunes, the silt of the playa lakes of the Harney Basin, the glacial cobbles and gravels in the high mountain valleys of the Wallowa Mountains, and the mud in the bottom of the present-day Willamette River channel.
	"tectonic" – Mixtures of unrelated pre-existing rocks that have been pushed around, mashed together, or reshaped by the large forces generated by collisions of the Earth’s crustal plates. Many of these rocks were originally formed by metamorphic processes in the lowest parts of the Earth’s crust. They were then crushed up against the continental plate edge by its collision with an oceanic plate or with another continental plate. These rocks are broken into large blocks that have little or no original relation to each other or to the rocks that now surround them. Because of their origins deep in the Earth’s crust, tectonic rocks, like serpentinite, gabbro, and greenstone, contain some of the Earth’s most exotic and precious minerals. In Oregon these rocks are found in only two areas, the Klamath Mountains of southwestern Oregon, and the Blue Mountains in the northeast corner of the state.
	volcanic – Any product of a volcanic eruption of magma/lava onto the Earth’s surface. The resulting rocks can have many different characteristics, depending upon the magma/lava’s original chemical composition and gas content and its interaction with water as it erupts. Volcanic rocks include both lava flows and ash, cinder and other fragmental rocks. Generally the background crystals in these rocks are fine-grained to glassy, but many of them also contain larger crystals that are visible to the naked eye and appear to “float” in the glassy background. Oregon’s volcanic history has been a restless one, and the predominant rocks in all parts of the state are volcanic. Volcanic features in Oregon range from the black basalt cliffs in the Columbia River Gorge to the red cinder cones of the Bend area, to the white pumice fields of the area east of Crater Lake.
	Info Query popup fields: General Lithology Type Geology Rock Type Geology General Unit Reference ID

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Faults Key

The Faults overlay shows fault traces and their certainties. When viewing the map, be sure to use the Info Query tool to display more detailed information.

Color	Fault Certainty
	certain (solid line)
	approximate (long dashed line)
	inferred (short dashed line)
	concealed (dotted line)
	Info Query popup fields: Fault Name Fault Type Certainty Direction Reference ID