Periodically, the ice dam would fail, resulting in a large catastrophic flood of ice- and dirt-filled water which rushed across northern Idaho and eastern and central Washington, down the Columbia River, through the Columbia River Gorge, and finally poured into the Pacific Ocean at the mouth of the Columbia River. Flood waters filled the Willamette River Valley, reaching Eugene, Oregon, more than 100 miles away.

When Lake Missoula burst through the ice dam and exploded downstream, it did so at a rate 10 times the combined flow of all the rivers of the world.

Along the floodwaters’ path, more than 50 cubic miles of earth and rock were removed, transported, and much was deposited as new landforms. The floods built gravel bars as tall as 400 feet and moved boulders weighing many tons and deposited them high on the valley walls. Most of the eroded material was carried out onto the floor of the Pacific Ocean, where extensive deposits of flood sediment have been identified hundreds of miles from the current mouth of the Columbia River. According to Geologist Richard Waitt of the U.S. Geological Survey (1985), the various limits on the ice sheet and the floods suggests that Glacial Lake Missoula existed for 2,000 to 2,500 years between 15,300 and 12,700 years ago, creating more than 40 and maybe up towards 60 separate flood events.

"At the end of the last Ice Age, a finger of the Cordilleran ice sheet crept southward into the Idaho panhandle, forming a large ice dam that blocked the mouth of the Clark Fork River, creating a massive lake 2000 feet deep and containing more than 500 cubic miles of water. Glacial Lake Missoula stretched eastward for some 200 miles and contained more water than Lake Erie and Lake Ontario combined. When the highest of these ice dams failed, lake water burst through, shooting out at a rate 10 times the combined flow of all the rivers of the world. This towering mass of water and ice literally shook the ground as it thundered toward the Pacific Ocean, stripping away hundreds of feet of soil and cutting deep canyons—”coulees”—into the underlying bedrock. With flood speeds approaching 65 miles per hour, the lake would have drained in as little as 48 hours. Over time the Cordilleran ice sheet continued moving south and blocked the Clark Fork River again and again, recreating Glacial Lake Missoula. Over approximately 2,500 years, the lake, ice dam and flooding sequence was repeated dozens of times, leaving a lasting mark on the landscape. ... They carved out more than 50 cubic miles of earth, piled mountains of gravel 30 stories high, created giant ripple marks the height of three-story buildings, and scattered 200-ton boulders from the Rockies to the Willamette Valley. Grand Coulee, Dry Falls, Palouse Falls—all were created by these flood waters, as were the Missoula and Spokane ground-water resources, numerous wetlands and the fertile Willamette Valley and Quincy Basin." Source:    U.S. National Park Service website, 2001, "Ice Age Floods", 2005, 2018.

"Quaternary deposits in the gorge are those of the cataclysmic Missoula (or Spokane) floods. The Cordilleran ice sheet from Canada advanced several times during the Pleistocene and covered parts of Washington, Idaho, and Montana. The ice formed dams on the Clark Fork River on the Idaho-Montana border and created glacial Lake Missoula. The lake covered 3,000 square miles of western Montana and held 600 cubic miles of water (Carson and Pogue, 1996). The ice dams failed repeatedly releasing gigantic glacial floods that swept across northern Idaho, through the Spokane Valley, southwestward across eastern Washington, and down the Columbia River Gorge enroute to the Pacific Ocean (Carson and Pogue, 1996). The Missoula floods are the largest known floods on Earth in the last two million years; the flow of water was ten times the combined flow of all the rivers of the world. In eastern Washington, the floods created the Channeled Scablands, an area studied by J. Harlen Bretz in the 1920s. Bretz was the first person to describe these gigantic glacial floods. The flood crest at Wallula Gap on the Columbia River at the Washington-Oregon border was about 1,200 feet as evidenced by glacial erratics that were left stranded on the hillside. The water poured down the Columbia Gorge and widened the valley by cleaning off all the soil and talus up to 1,000 feet elevation as far as The Dalles, Oregon. By the time it reached Crown Point, the surface of the last flood had dropped to about 600 feet elevation (Allen, 1979). There may have been more than 40 major glacial floods (Waitt, 1980) recorded by bedded slack water deposits (rhythmites). The average interval between Missoula floods was about 30 years (Waitt and others, 1994). The last flood occurred 13,000 years ago." Source:    David K. Norman and Jaretta M. Roloff, 2004, "A Self-Guided Tour of the Geology of the Columbia River Gorge -- Portland Airport to Skamania Lodge, Stevenson, Washington", Washington State Division of Geology and Earth Resources, Open File Report 2004-7.

"... up to 250 cubic miles of water and 50 cubic miles of ice and debris were trying to rush through this gap [Wallula Gap] all at the same time. The gap formed a hydrologic dam, a constriction that ponded water in back of it until it all could rush through. This became the first Missoula Flood lake formed in the lower Columbia River system. We call it Lake Lewis after Meriwether Lewis of the Corps of Discovery who came through the area in 1805 on the Lewis and Clark expedition." [Allen, et.al., 2009]

"Up to 264 cubic miles of water were ponded during each of the later, cleaner floods for perhaps a couple of weeks. These temporary lakes covered over 3,000 square miles of the Pasco and Quincy Basins, flooded the Yakima and Walla Walla River Valleys, and went 100 miles up the Snake River. Overall, Lake Lewis stretched about 120 miles from east to west and 60 miles from north to south. It probably was up to 800 feet deep at the Tri-Cities." [Allen, et.al., 2009]

"Lake Condon"   The constriction at The Dalles created "Lake Condon", which covered approximately 1,500 square miles from The Dalles to Umatilla.

"The Columbia River Gorge, starting at The Dalles, became the next hydrologic dam for the Missoula Flood waters, slowing down the flows and forming a second large lake that extended from Wallula Gap to The Dalles. It had a surface area of over 1,500 square miles and covered the present day Umatilla and The Dalles Basins. It rose to an elevation of over 1,000 feet and most likely reached to 1,100 feet (the height of the erosion lines in Wallula Gap). This lake was named to honor Thomas Condon, one of the great pioneers in geology in Oregon. During each flood, soft sediments and the upper basalt flows in the basin on either side of the river were eroded away and reworked in the initial flows." [Allen, et.al., 2009]

"Lake Allison":   The constriction at Kalama created a backwater lake, known as "Lake Allison". This lake filled the Willamette River Valley as far as Eugene, Oregon, over 100 miles away, with a measured height of 400 feet at Oregon City and an estimated height of 380 feet at Eugene. The area covered was approximately 3,000 square miles. The flood waters dumped thick layers of Palouse Silt, making the Willamette Valley one of the most fertile agricultural lands in the country.

"Each flood filled the Willamette Valley as far south as Eugene to nearly 400 feet in elevation, leaving deposits in the valley that consist of layered rhythmites known as Willamette Silt. The floods entered the Willamette Valley through the Oregon City Gap. More than 300 known groups of erratic boulders were dropped by melting icebergs around the margin of ephemeral Lake Allison. The floods also poured west through the Lake Oswego Gap into the Tualatin Valley, filling it to at least 350 feet elevation." [Allen, et.al., 2009]

"The Willamette Silt first described by Allison (1953) is a widespread deposit of bedded sand and silt which overlies several of the younger land surfaces above the flood plains of the present stream in the Valley. It varies in thickness from 150 feet at Newberg to 70 feet in Salem to 20 feet at Irish Bend (south of Corvallis) to a few feet at Eugene. It contains up to 50 rhythmites, like those found in the Walla Walla and Yakima Valleys of Washington. Oregonians can thank Washington for their rich soil in the Willamette Valley, for the Willamette Silts were originally Palouse Silts before the Missoula Floods transported them there." [Allen, et.al., 2009]

• Columbia River Mile (RM) 329 ... Pasco Basin
• RM 313 ... Wallula Gap
• RM 313 ... Twin Sisters (Two Sisters)
• RM 298 ... Hat Rock and Boat Rock
• RM 292 ... Umatilla
• RM 243 ... Arlington
• RM 243 to RM 227 ... Alkali Canyon, Jones Canyon, Blalock Canyon, and Philippi Canyon
• RM 218 ... John Day River
• RM 216 ... John Day Dam Gap
• RM 210 and RM 205 ... Stonehenge and Maryhill Museum
• RM 204 ... Deschutes River
• RM 203 ... Miller Island
• RM 200 ... Fairbanks Gap
• RM 194 ... Horsethief Butte
• RM 189 ... The Dalles
• RM 186 ... Turbulence-cut Bench Lines
• RM 185 to RM 181 ... Rowena Gap/Ortley Gap
• RM 181 ... Kolk Pond, Mayer State Park
• RM 180 ... Klickitat River and Lyle
• RM 180 ... Rowena Crest
• RM 180 ... Mima Mounds
• RM 180 ... Tom McCall Nature Preserve
• RM 175 ... Mosier
• RM 175 to RM 171 ... Bingen Gap
• RM 170 ... White Salmon
• RM 169 ... Hood River
• RM 166 ... Ruthton Point
• RM 160 ... Dog Mountain Gap
• RM 146 ... Bonneville Dam
• RM 142 ... Beacon Rock
• RM 136 ... Multnomah Falls
• RM 132 and RM 129 ... Phoca Rock and Rooster Rock
• RM 129 ... Crown Point
• RM 120 ... Troutdale
• RM 120 to RM 102 ... Willamette River Valley
  • Rocky Butte
  • Willamette Meterorite, West Linn
  • Oregon City
  • Camassia
  • Flood Deposits
  • Glacial Erratic, Multnomah County, Oregon
  • Glacial Erratic, Yamhill County, Oregon
• RM 120 to RM 80 ... Vancouver Basin
  • Lacamas Lake and Round Lake
  • Prune Hill
  • Mill Plain Bar
  • Sand and Gravel
  • Glacial Erratics, Clark County, Washington
  • Glacial Erratic, Ridgefield NWR, Washington
  • Burnt Bridge Creek and Salmon Creek
  • Ripple Marks
  • Ridgefield National Wildlife Refuge
  • Lewis River and the East Fork Lewis River
• RM 86 ... St. Helens, Oregon
• RM 82 ... Woodland, Washington
• RM 71 ... Kalama Gap
• RM 67 ... Longview and Kelso
• RM 50 ... Clatskanie, Oregon
• RM 40 ... Nicolai Ridge and Clatsop Crest
• RM 0 ... Astoria and the Pacific Ocean

Buttes located west of Richland are between 400 to 500 feet elevation.

Missoula Flood heights at the Wallula Gap were measured at 1,250 feet (Allen and Burns, 1986).

The U.S. National Elevation Dataset (2018) lists the Twin Sister's elevation at 449 feet.

The Missoula Flood waters were over 1,200 feet at this point.

Lewis and Clark passed Hat Rock on October 19, 1805, and gave it it's name.

"... SW. 14 miles to a rock in a Lard. resembling a hat just below a rapid at the lower Point of an Island in the Midl: of the river ..." [Clark, October 19, 1805, first draft]

The U.S. National Elevation Dataset (2018) lists Hat Rock's elevation at 469 feet and Boat Rock's elevation at 509 feet. The Missoula Flood waters were over 1,200 feet at this point.

"The John Day valley is mantled by rhythmically bedded sand and silt deposits from its mouth to more than 30 kilometers [approximately 20 miles] upstream. These deposits have not been examined in detail [note, 2009 report], but apparently they were deposited by several Missoula floods that backflooded up the valley, probably by smaller flows that did not overtop the divides here." [O'Connor and Burns, 2009]

Missoula Flood heights at the mouth of the John Day River, located at Columbia River Mile (RM) 218, were measured at 1,140 feet (Allen and Burns, 1986).

"The Nook", rising over 1,000 feet above the waters of Lake Umatilla, is the high point on the right bank of the John Day River. The U.S. National Elevation Dataset (2018) lists it's elevation at 1,270 feet. During maximum Missoula Flood height, only the top 130 feet of The Nook's top was above water.

The height of the Lake Umatilla pool (the reservoir behind the John Day Dam) is 268 feet (full pool, U.S. Army Corps of Engineers, 2018).

Missoula Flood heights at the John Day Dam Gap, were measured at 1,130 feet (Allen and Burns, 1986). Two miles upstream lies the mouth of the John Day River where Missoula Flood heights were measured at 1,140 feet (Allen and Burns, 1986).

According to Allen, et.al. (2009):

"The Columbia River, four miles below the mouth of the John Day, passes through a narrows, now the site of the John Day Dam. ... The floodwaters flowing through these narrows and draining Lake Condon moved at a rate of up to 40 miles per hour." [Allen, et.al., 2009]

According to Allen, et.al. (2009):

"A high bench up to a mile wide was cut into the north wall of the [Columbia River] canyon on which Maryhill Museum and the Stonehenge Monument now rest. Several large ice-rafted erratics have been found here above 800-feet elevation, one of them at 860 feet." [Allen, et.al., 2009]

According to Norman, et.al. (2004):

"Maryhill Museum sits on a bench of nearly flat-lying lava flows of the 14.5-million-year-old Priest Rapids Member of the Wanapum Basalt." [Norman, et.al, 2004]

The U.S. National Elevation Dataset (2018) lists Stonehenge's elevation at 561 feet and Maryhill Museum's elevation at 774 feet.

The U.S. National Elevation Dataset (2018) lists Horsethief Butte's elevation at 492 feet.

The Missoula Floods kolk pond behind the Columbia Gorge Discovery Center was formed by "strong Floods whirlpools plucking out the bedrock" (IAFI Field Trip Guide).

According to the Ice Age Floods Institute (2018):

"... from this viewpoint [Columbia Gorge Discovery Center] a few thin horizontal benches can be seen on the gently dipping hillsides across the river. These benches are also thought to have been cut by turbulent flood waters rushing into Rowena Gap." [Ice Age Floods Institute, 2018]

Missoula Flood heights at the Ortley Gap (Rowena Gap) were measured at 1,000 feet (Allen and Burns, 1986).

According to Allen, et.al, (2009):

"Between The Dalles and Hood River, soil and talus were swept from the valley walls, leaving the series of clean steps we now see on the barren lava flows of Columbia River Basalt. ... The almost vertical 600-foot-high cliffs here were overtopped by at least 200 feet of water which cleaned off much of the overlying The Dalles Formation." [Allen, et.al., 2009]

According to Allen and Burns (1986):

"Between The Dalles and Hood River, soil and talus were swept from the valley walls, leaving the series of clean steps we now see on the barren lava flows of Columbia River Basalt. At many places the accumulations of talus, which one would expect to see after 15,000 years at the base of the cliffs, have yet to form substantial slopes. Just west of Mayer State Park (US 30), the river makes an abrupt turn to the north. This change in the course of the floods caused the cliffs to be undermined so extensively that a great landslide developed, down which the Scenic Highway swings in a series of turns (Rowena Loops)." [Allen and Burns, 1986]

According to Allen, et.al. (2009):

"The almost vertical 600-foot-high cliffs here were overtopped by at least 200 feet of water, which cleaned off much of the overlying The Dalles Formation and left several scabland channels, one of them by the highway containing a small kolk lake. Deposits of sands and gravels from the Missoula Flood waters were spread across the top of this plateau where today one can visit the Rowena Overlook and Tom McCall State Park. In the last 15,000 years, these sand and gravel deposits have been shaped into mima mounds. These deposits are about 30 feet across and five feet high and rest on the barren basalt bedrock." [Allen, et.al., 2009]

The Missoula Floods also left behind small rounded depressions in the basalts which eventually filled with water and are now called "kolk lakes". The trails at Tom McCall pass by two such lakes.

According to Waitt, et.al., (2009):

"West of The Dalles and Rowena Gap we pass the town Mosier in a sysclinal valley. Like the bars at Petersburg and Fairbanks, Missoula flood flow spilling over a divide from Columbia River to Mosier Creek deposited a large delta of southwest-dipping foresets of cobble-pebble gravel and sand." [Waitt, et.al., 2009]

Missoula Flood heights at Bingen Gap were measured at 950 feet (Allen and Burns, 1986).

"From Hood River east, marks of the Missoula floods become evident; the town of White Salmon (Washington side) sits atop a large gravel bar, with scrubbed hillslopes flanking the upstream constriction. Likewise at Lyle, also on the Washington side ... " [O'Connor and Burns, 2009]

According to Waitt, et.al., (2009):

"The north-side town of White Salmon is built upon a large pendant bar in the lee of Bingen Gap. One of the larger bars in [the] Columbia Gorge." [Waitt, et.al., 2009]

[More]

Missoula Flood heights at Hood River, Oregon, were estimated at 925 feet (Allen and Burns, 1986).

Missoula flood deposits form a late Pleistocene capping of sand and silt as thick as 30 meters [100 feet] in some parts of the Hood River Valley (Scott, et.al., 1997).

According to D.K. Norman, et.al. (2004):

"The Hood River Valley was inundated by backwater from the Missoula floods. Newcomb (1969) reported "fine-grained lacustrine deposits" as high as 800 feet, probably slackwater deposits of Missoula floods. The highest ice-rafted erratics in the Hood River Valley are betwen 840 and 880 feet. If this was the maximum stage achieved by the largest flood, the water surface dropped substantially through Bingen Gap (O'Connor and Waitt, 1994)." [Norman, et.al., 2004]

According to Waitt, et.al., (2009):

"Backwater from the Missoula floods inundated Hood River valley, where Newcomb (1969) reported "fine-grained lacustrine deposits" as high as 245 meters (800 feet). High ice-rafted erratics in the Hood River valley lie between 255 and 270 meters (840-880 feet) altitude. If this was the maximum stage achieved by the largest flood, the water surface dropped substantially through Bingen Gap." [Waitt, et.al., 2009]

"The best examples of polished, fluted, and scoured basalt surfaces known at high level in [the] Columbia Gorge are riverward of the Columbia River Gorge Hotel, a 1921 structure on the National Historic Register." [Waitt, et.al., 2009]

Missoula Flood heights at the Dog Mountain Gap were measured at 875 feet (Allen and Burns, 1986).

According to Allen, et.al., (2009):

"At the west end of the Gorge lies an additional large landslide just to the west of Crown Point. Missoula Floodwaters undercut the cliffs on the south side of the river producing a large landslide that transported part of the Crown Point inter-canyon flow of the Columbia River Basalts to the river bottom, still in an upright position. The resulting monolith was ultimately named Rooster Rock. Even today, this landslide continues to creep, as evidenced by the slowly sinking old highway road at its crest. Another large rock (also transported by a Missoula Flood landslide) lies in the middle of the river close to the Cape Horn basalt flow. Lewis and Clark gave it the name of Seal Rock, or Phoca Rock, for the seals that rested there after following the salmon upstream." [Allen, et.al., 2009]

According to Norman and Roloff in their "Self-guided Tour of the Geology of the Columbia River Gorge" (2004, Washington Division of Geology and Earth Resources, OFR 2004-7):

"Rooster Rock is a landslide of a portion of the Crown Point intracanyon fill. You can see the scar where the slide came from on the cliff above. Note the rotated-bedded palagonite cpped by fan-jointed columns and hackly entablature in the slide. Several jumbled blocks are present. Rooster Rock itself is a spire from the entablature." [Norman and Roloff, 2004]

"As the floods emerged from the Gorge at Crown Point Gap which is only two miles wide, they crested above the Vista House at over 700-feet elevation, then plunged down within about three miles to 550-feet elevation, with a width of about five miles." [Allen, Burns, and Burns, 2009]

"... prominent Crown Point (capped by the Vista House) on the south side of the river, formed one of the major constrictions along the entire Missoula Flood route. While flood evidence is sparse in the "green hell" section of the gorge ... the maximum stage of the largest Missoula flood descended from 250 to 270 meters (820 to 860 feet) above sea level upstream of Crown Point to 120 to 150 meters (400 to 500 feet) above sea level in the Portland basin. Flood flow through this section was probably critical with velocities exceeding 35 meters/second (115 feet/second). Hydraulic ponding behind these Columbia River Gorge constrictions probably impeded flow as far upstream as [the] Pasco Basin." [O'Connor and Burns, 2009]

The U.S. National Elevation Dataset (2018) lists Crown Point's elevation at 722 feet.

Missoula Flood heights at the Crown Point Gap, were measured at 700 feet (Allen and Burns, 1986).

Missoula Flood heights at Troutdale, were estimated at 540 feet (Allen and Burns, 1986).

• Willamette River Valley, Rocky Butte ...

  Rocky Butte stood in the path of the Missoula Floods. The rushing flood waters heading down the Willamette Valley eroded the land on the upstream side of the Butte, similar to how a stream erodes the sediment on the upstream side of a rock in its path. Today on the east side of Rocky Butte, Interstate 205 and Interstate 84 follow the broad channels carved by the floods.

  According to Scott (1997):

  "... Rocky Butte, an early Pleistocene basaltic andesite volcano of the Boring Lava. ... During peak flows of the latest Pleistocene Missoula floods, high velocities and turbulence induced by the submerged butte eroded huge scour pits on its upstream side; downstream, gravel bars many kilometers long were deposited. I-84 curves around the south and east sides of the butte in scour pits." [Scott, 1997, Geologic History of Mount Hood Volcano, Oregon, USGS Open-file Report 97-263]

• Willamette Meteorite, West Linn ...

  "The Willamette Meteorite is the largest meteorite ever discovered in the United States. It is now on display in the American Museum of Natural History in New York City. Although the meteorite was discovered on a hilltop in the Willamette Valley, scientists believe the 15.5 ton iron-nickel mass landed on the Cordielleran ice sheet in British Columbia before being carried southward by the advancing ice sheet and floated into the Willamette Valley embedded in an iceberg during Missoula Floods." [Minervini, et.al., 2003]

  "The Willamette Meteorite is the largest ever found in the United States and the sixth largest in the world. This 31,107-pound mass of nickel and iron was found in 1902 on the top of a spur on the east side of the Tualatin Valley two miles northwest of the town of West Linn at an elevation of 380 feet. ... In 1985, Richard Pugh discovered several granite erratics only a few feet from the site of th emeteorite. The meteorite did not fall in Oregon but originally descended onto the ice lobe in the Purcell Trench or farther north on the Cordilleran Ice Sheet in Canada. It moved slowly south down the trench to near Lake Pen Oreille and from there was carried down in an iceberg during one of the Missoula Floods. A park has now been opened in Oregon City with a replica of the meteorite and eight plaques explaining its history and connection to the Missoula Floods." [Allen, Burns, and Burns, 2009]

  The park mentioned above is Fields Bridge Park, now a part of the Ice Age Floods National Geologic Trail.

• Willamette River Valley, Oregon City Water Gap ...

  As Missoula Flood waters rushed down the Columbia River Valley they reached the Kalama Gap constriction at Columbia River Mile 71. The area behind the construction filled with water creating "Lake Allison". Waters of Lake Allison flowed south entering the Willamette Valley through the Oregon City and Lake Oswego Water Gaps, and eventually reached as far south as Eugene, Oregon, over 100 miles south of the Columbia River.

• Willamette River Valley, Camassia ...

  Camassia Nature Preserve is a 26 acre "park" located in West Linn, Oregon, and was named for the common camas (Camassia quamash), which blooms among the basalt blocks in April and early May. The preserve hosts more than 300 plant species.

  According to The Nature Conservancy's Camassia Natural Area's website (2018):

  "The rocky plateau was exposed 12,000- 19,000 years ago when the Bretz Floods poured down the present Columbia River Gorge and far into the Willamette Valley. The floods swept soil and vegetation from parts of the valley and deposited granitic boulders (called "glacial erratics") from as far away as Canada." [The Nature Conservancy website, 2018]

  [More]

• Willamette River Valley, Missoula Flood Deposits ...

  "Each flood filled the Willamette Valley as far south as Eugene to nearly 400 feet in elevation, leaving deposits in the valley that consist of layered rhythmites known as Willamette Silt. ... The Willamette Silt first described by Allison (1953) is a widespread deposit of bedded sand and silt which overlies several of the younger land surfaces above the flood plains of the present streams in the Valley. It varies in thickness from 150 feet at Newberg to 70 feet in Salem to 20 feet at Irish Bend (south of Corvallis) to a few feet at Eugene. ... Oregonians can thank Washington for their rich soil in the Willamette Valley, for the Willamette Silts were originally Palouse Silts before the Missoula Floods transported them there." Source:    John Eliot Allen, Marjorie Burns, and Scott Burns, 2009, "Cataclysms on the Columbia: The Great Missoula Floods", Ooligan Press.

• Willamette River Valley, Glacial Erratic, Multnomah County ...

  As of June 2003, the U.S. Geological Survey's Missoula Flood Glacial Erratic database contained "records of 400 glacial erratics and their locations; however, approximately 28 of these locations are thought to be duplicates". [Minervini, et.al., 2003, USGS OFR-03-408]
  
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• Willamette River Valley, Glacial Erratic, Yamhill County ...

  The "Sheridan Erratic", often called the "Bellevue Erratic", is located on the west side of the Willamette Valley, just off of Oregon Highway 18, and halfway between the Oregon communities of Sheridan and McMinnville. According to Dr. Jim O'Connor in an interview with the Yamhill Valley News-Register" (2005):   "the 90-ton rock, which sits atop a rise about a half mile from the site entrance, probably came in on an iceberg around 15,000 years ago, transported by one of the Missoula floods, the biggest known fresh water floods in history. The erratic rock is at an elevation of 300 feet and the floods probably topped that by 100 feet." The News-Register goes on to say:   "More than 400 ice-rafted rocks have been identified along the flood plain ... they are different in composition from the local bedrock, thus are called "erratic" and the one near Sheridan is the largest known glacial erratic in the Willamette Valley." Geologically the rock is an argillite boulder from Canada and is believed to be 600 million years old. It was originally part of the sea-floor. It once weighed 160 tons and measured nearly 21 x 18 x 5 feet. Today the boulder sits in many pieces with the largest being nearly 18 x 13 x 5 feet, and weighs in at 90 tons. Vandalism and souvenier hunters have taken the rest.
  
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• Vancouver Basin, Lacamas Lake and Round Lake ...

  Lacamas Lake and Round Lake, located just north of Camas, Washington, are two kolk lakes which lie within a Missoula Flood trough created as the massive floods left the Columbia Gorge and surged west, reaching the Kalama Gap constriction, and backing flood waters over the Vancouver Basin and the Willamette Valley.

  According to Evarts and O'Connor (2008):

  "In latest Pleistocene time, huge Columbia River floods from glacial Lake Missoula inundated the Portland Basin, eroding channels such as the Lacamas Lake trough but also leaving immense bars of sand and gravel and a blanket of sand, silt, and clay in slack water areas." [Evarts and O'Connor, 2008]

  According to Allen, et.al. (2009):

  "From Crown Point Gap, the water poured northwestward across the present sites of Washougal and Camas with a depth of nearly 500 feet. It swept up the Washougal and Little Washougal valleys and across the divide past Woodburn Hill north of Washougal into the valley of Lacamas Creek, where it was joined by similar torrent that had surged up Lacamas Creek, scouring out the kolk depression now occupied by Lackamas Lake. Only the upper 100 feet of Woodburn Hill and the upper 200 feet of the higher Prune Hill, west of Camas, stood above the waters. The entire Vancouver plains surface was inundated as far north as Woodland, 35 miles to the northwest, covering over 275 square miles of the basin in Washington." [Allen, et.al., 2009]

• Vancouver Basin, Prune Hill ...

  Prune Hill, a Boring Lava cone, has a high point of 751 feet. The small peak delineates the eastern end of the "Vancouver Basin". Only the upper 200 feet of Prune Hill stood above the Missoula Flood waters. (Allen, et.al., 2009)

  According to Allen, et.al. (2009):

  "As the floodwaters hit Prune Hill (a Boring Lava volcano to the west of Camas), a large pendant bar formed in back of it and extends over five miles to the west. Prune Hill acted like a boulder in the streambed, slowing down the flow, especially downstream, and allowing the load of the water to deposit sediment. (Humans have been mining sediment from Mill Plain Pendant Bar for over 100 years)." [Allen, et.al., 2009]

• Vancouver Basin, Mill Plain Bar ...

  According to Evarts (2006):

  "Mill Plain [east Vancouver, Washington] is the surface of a huge bar deposited by the floods in the lee of Prune Hill at Camas ... These deposits, as thick as 40 meters [130 feet] or more, were apparently deposited by multiple floods (Waitt, 1996). Similar gravel accumulated as a fan west of Proebstel, where floodwaters discharged northwestward through the trough now occupied by Lacamas Lake (Trimble, 1963; Waitt, 1994). Before the floods, Lacamas Creek probably flowed westward to Burnt Bridge Creek but was diverted sharply southeastward to Lacamas Lake by the fan near Proebstel. Well logs indicate that the gravel grades northward to predominantly sand near Hockinson." [Evarts, 2006]

  
  [More]

• Vancouver Basin, Sand and Gravel ...

  The Vancouver and Orchards Geologic Map Quadrangle (O'Connor, et.al., 2016) describe the composition and depth of the Missoula flood gravel deposits.

  Vancouver and Orchards Quadrangles:
  "Gravel facies -- Unconsolidated, gray, stratified, bouldery to cobbly gravel and sand, deposited in thick sheets over older basin-fill deposits on upland areas flanking the Columbia River; organized into prominent, large bar-and-channel complexes on Mill Plain and Fourth Plains. On uplands of Mill Plain and Fourth Plains in the eastern area [map extends to NE 164th], several quarries show more than 59 feet of crudely stratified and poorly sorted coarse gravel and sand, commonly deposited in tall (locally >16 feet), steeply dipping (as much as 35 degrees) foresets; former exposures to west showed similar features. In east part of map area, many rounded boulders exceed 3 feet diameter. Many active and historic quarry exposures in upland areas reveal fining westward, and away, from the Columbia River. On Mill Plain, north-dipping foresets indicate transport by northward flow out of the Columbia valley. Sweeping unconformities visible in large, fresh exposures likely separate deposits of individual floods. Texturally and compositionally variable; most clasts derived from Columbia River Basalt Group but includes blocks of Troutdale Formation and Pliocene to Quaternary volcanic rocks, all probably entrained in the western Columbia River Gorge. On uplands, deposits overlie older basin-fill deposis, but cataclysmic-flood gravel bars step down into the Columbia River valley and locally thicken to the south and west, perhaps to as much as 200 feet thick along I-5 through Vancouver. West of Vancouver, a possibly inset bench may have been deposited by later, smaller floods. Beneath Holocene Columbia River floodplain deposits, cataclysmic-flood gravel coats and partly fills the late-glacial valley, a valley bottom incised at least 230 feet below sea level." [O'Connor, et.al., 2016, Scientific Investigations Map 3357]

• Vancouver Basin, Glacial Erratics ...

  Numerous erratics glacial erratics were ice-rafted and deposited in the Vancouver Basin. Four are "on display" at the Washington State University's Vancouver Campus. One is tucked in a forgotten corner near the Greenhouse, and the other three are located on a slope on the east side of campus. All of the erratics are not in their original location. One was found in a field in east Vancouver, and the other three (which use to be one big erratic) were moved after originally being unearthed during construction of the Science building.
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  Erratic found in east Vancouver, near 162nd Avenue:

  "It all started the winter of 2003, when a flash of white caught a WSU graduate student’s attention as he drove along 162nd Avenue in east Vancouver. Investigating further, he quickly realized he was looking at a granite Missoula Ice Age Flood erratic. The boulder, roughly the size of a park bench, had black and white speckles characteristic of the granite in northern Idaho. This area is made up of basalt, not granite. So granite would have been transported by the Missoula Ice Age Floods. The rock was salvaged from the field where a housing subdivision was being graded and a road was being widened on 162nd Avenue. A small crew of county workers used an excavator to hoist the rock, swinging it onto the back end of a flatbed trailer. The county gave the historic rock to WSU Vancouver for display. It is now located on the east side of the Engineering Building near the entrance to the greenhouse." Source:    "waymarking.com" website, 2018, "WSU's Missoula Ice Age Flood Erratic, Vancouver, Washington.

  
  

  Erratic(s) found at the Science Building:

  "Missoula flood ice-rafted erratics:   Latitude: 45°43'57", Longitude: 122°37'54", Lithology: Granitic, Comments: Three > 3-foot- (1 meter) diameter boulders, derived from a single large erratic found during excavation of Washington State University Science building; original location 45°43'57", 122°38'04"." Source:    O'Connor, et.al., 2016, U.S.G.S. Scientific Investigations Map 3357

  
  

  Erratic, Carty Unit, Ridgefield NWR, Ridgefield, Washington:

  "A granitic boulder is the remnant of cataclysmic Missoula Ice Age floods that occurred about 15,000 years ago." Source:    "waymarking.com" website, 2018, "Erratic, Ridgefield National Wildlife Refuge, Ridgefield, Washington.

• Vancouver Basin, Burnt Bridge Creek and Salmon Creek ...

  Today's Burnt Bridge Creek carved a channel through Missoula Flood deposits and merges into Vancouver Lake on its east side. Four miles north, today's Salmon Creek carved its channel into Missoula Flood deposits. Salmon Creek merges into Lake River at Lake River Mile (RM) 9.

  "From Crown Point Gap, the water poured northwestward across the present sites of Washougal and Camas with a depth of nearly 500 feet. It swept up the Washougal and Little Washougal valleys and across the divide past Woodburn Hill north of Washougal into the valley of Lackamas Creek, where it was joined by a similar torrent that had surged up Lackamas Creek, scouring out the kolk depression now occupied by Lackamas Lake. ... Northwest of Lackamas Lake, one broad channel paralleled the main Columbia River channel courses westward along Burnt Bridge Creek; other split off to the northwest and continued on into Salmon Creek and to the north into the well-develped ridge-and-swale area along Mill Creek." [Allens, Burns, and Burns, 2009]

• Vancouver Basin, Ripple Marks ...

  (to come)

• Vancouver Basin, Ridgefield National Wildlife Refuge ...

  While some areas of the Vancouver Basin received massive deposits of sand and gravel, in other areas the power of the Missoula Flood waters scoured the surface area down to the Columbia River Basalt bedrock, exposing huge outcrops of rock. Cobblestone quarries developed and the resulting "Belgian Blocks" were used in the paving of some Portland streets.

• Vancouver Basin, Lewis River and the East Fork Lewis River ...

  The Washington community of Woodland is located on the Lewis River floodplain, an area once inundated by the massive floodwaters of the Missoula Floods. The Lewis River and its tributary the East Fork Lewis River cut their channels into Missoula Flood deposits.
  
  

  QUATERNARY DEPOSITS. Alluvial Deposits: "During glacial maxima, sea level was as much as 400 feet (120 meters) lower than at present. The Columbia River in response deeply incised its bed, flowing through a narrow valley about two kilometers west of the map area (Ridgefield Quad). The Lewis and East Fork Lewis Rivers presumably also adjusted to lower base level at these times. Late in the last glacial period, huge glacier-outburst floods from Glacial Lake Missoula coursed down the Columbia River valley and hydraulically ponded in the Portland Basin; silt and fine sand that settled out of this temporary lake now cover much of the map area. As sea level rose during the late Pleistocene and Holocene, the late Pleistocene valleys gradually filled with sediment." Cataclysmic-flood deposits: "During the last glacial maximum in late Pleistocene time, an ice dam impounded Glacial Lake Missoula in western Montana. The dam failed repeatedly, releasing floods that coursed down the Columbia River and into the Portland Basin. The sediment-laden floodwaters were hydraulically constricted by the narrow reach of the Columbia River valley north of (downstream from) the Ridgefield quadrangle. The constriction caused temporary ponding in the Portland Basin and tribuatry valleys to levels as high as 400 feet (120 meters). Radiocarbon ages, paleomagnetic measurements, and tephrochronologic data indicate that the last glacial episode of floods occurred chiefly between about 17,000 and 13,000 14C years B.P. Similar episodes of cataclysmic flooding probably occurred earlier in the Quaternary. During each flood, the suspended load of fine sand and silt settled out of the temporarily ponded floodwaters. In the northern Portland Basin, multiple floods collectively built up deposits of laminated micaceous sediments as thick as 100 feet (30 meters). These slack-water deposits (Qfs), which grade almost imperceptively northward from fine sand to silt, now mantle the entire surface of the Ridgefield quadrangle south of the East Fork Lewis River. Partly eroded flood deposits lie north of the river between 200 and 300 feet (60 and 75 meters) elevation, and local unmapped patches of micaceous silt are found at elevations up to 400 feet (120 meters)." Late Pleistocene and Holocene alluvial deposits: "Remnants of a terrace with surface elevations of 110 to 140 feet (33 to 43 meters) lie along the south bank of the Lewis River directly downstream from its confluence with the East Fork Lewis River. The terrace deposits (Qtd) consist of unconsolidated, poorly sorted sandy pebble gravel and lithic sand overlain by micaceous silt of Missoula-floods origin (Qfs). Terrace-gravel clasts are chiefly Tertiary volcanic rocks eroded from the Cascade Range, indicating that the terrace sediment was carried by the Lewis River rather than the Columbia." Source:    R.C. Evarts, 2004, "Geologic Map of the Ridgefield Quadrangle, Clark and Cowlitz Counties, Washington", USGS Scientific Investications Map 2844.

In the St. Helens area the power of the Missoula Flood waters scoured the surface area down to the Columbia River Basalt bedrock where huge outcrops of rock were exposed. These outcrops were later quarried and the resulting "Belgian Blocks" were used in the paving of some Portland streets.

Missoula Flood heights at the Kalama Gap, were measured at 400 feet (Allen and Burns, 1986).

"Glacial Lake Missoula, impounded by the Purcell Trench lobe of the late Pleistocene Cordilleran Icesheet, repeatedly breached its ice dam, sending floods as large as 2,500 cubic kilometers [290 cubic miles] racing across the Channeled Scabland and down the Columbia River valley to the Pacific Ocean. Peak discharges for some floods exceeded 20 million cubic meters per second. At valley constrictions along the flood route, floodwaters temporarily ponded behind each narrow zone. One such constriction at Kalama Gap -- northwest of Portland -- backed water 120-150 meters [400-500 feet] high in the Portland basin, and backflooded 200 kilometers [125 miles] south into Willamette Valley. Dozens of floods backed up into the Willamette Valley, eroding "scabland" channels, and depositing giant boulder gravel bars in areas of vigorous currents as well as bedded flood sand and silt in backwater areas. Also, large chunks of ice entrained from the breached glacier dam rafted hundreds of "erratic" rocks, leaving them scattered among the flanking foothills and valley bottom." Source:    Minervini, J.M., O'Connor, J.E., and Wells, R.E., 2003, "Maps showing inundations depths, ice-rafted erratics, and sedimentary facies of late Pleistocene Missoula Floods in the Willamette Valley, Oregon", U.S. Geological Survey Open-file Report 03-408.

According to Allen, et.al. (2009):

"[Between Portland and Astoria] there were two major constrictions in the Columbia River Valley, at Kalama and at Clatskanie. ... Floodwaters remained near the 400-foot contour level through Kalama, but then began to fall. After the Kalama narrows, the water was reduced to 275 feet deep at Clatskanie and near sea level at Astoria. Woodland and St. Helens were both beneath 400 feet of water. Interpolating between Kalama and Clatskanie suggests that both Kelso and Longview were at least 300 feet below the surface of the floods." [Allen, et.al., 2009]

According to Allen, et.al. (2009):

"Nicolai Ridge opposite Cathlamet, Washington is an outstanding example of a basalt ridge undercut by flood erosion resulting from an abrupt north bend of the course of the river. Abnormal steepening continues for another five miles on the south side of the river to Aldrich Point." [Allen, et.al., 2009]

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