Cordilleran Ice Sheet

The Cordilleran ice sheet was a major ice sheet that periodically covered large parts of North America during glacial periods over the last ~2.6 million years. This included the following areas:

The ice sheet covered up to 2.5 million square kilometres at the Last Glacial Maximum and probably more than that in some previous periods, when it may have extended into the northeast extremity of Oregon and the Salmon River Mountains in Idaho. It is probable, though, that its northern margin also migrated south due to the influence of starvation caused by very low levels of precipitation.

At its eastern end the Cordilleran ice sheet merged with the Laurentide ice sheet at the Continental Divide, forming an area of ice that contained one and a half times as much water as the Antarctic ice sheet does today. At its western end it is currently understood that several small glacial refugia existed during the last glacial maximum below present sea level in the now-submerged Hecate Strait and on the Brooks Peninsula in northern Vancouver Island. However, evidence of ice-free refugia above present sea level north of the Olympic Peninsula has been refuted by genetic and geological studies since the middle 1990s. The ice sheet faded north of the Alaska Range because the climate was too dry to form glaciers.

Unlike the Laurentide ice sheet, which is believed to have taken as much as eleven thousand years to fully melt, it is believed the Cordilleran ice sheet, except for areas that remain glaciated today, melted very quickly, probably in four thousand years or less. This rapid melting caused such floods as the overflow of Lake Missoula and shaped the topography of the extremely fertile Inland Empire of Eastern Washington.

Map missoula floods
Southern edge of the ice sheet. It extended north along the Pacific coast and covered the Alaska Peninsula.

Sea levels during glaciation

Because of the weight of the ice, the mainland of northwest North America was so depressed that sea levels at the Last Glacial Maximum were over a hundred metres higher than they are today (measured by the level of bedrock).

However, on the western edge at the Haida Gwaii (formerly known as the Queen Charlotte Islands), the lower thickness of the ice sheet meant that sea levels were as much as 170 metres lower than they are today, forming a lake in the deepest parts of the strait. This was because the much greater thickness of the centre of the ice sheet served to push upwards areas at the edge of the continental shelf in a glacial forebulge. The effect of this during deglaciation was that sea levels on the edge of the ice sheet, which naturally deglaciated first, initially rose due to an increase in the volume of water, but later fell due to rebound after deglaciation. Some underwater features along the Pacific Northwest were exposed because of the lower sea levels, including Bowie Seamount west of the Haida Gwaii which has been interpreted as an active volcanic island throughout the last ice age.

These effects are important because they have been used to explain how migrants to North America from Beringia were able to travel southward during the deglaciation process due purely to the exposure of submerged land between the mainland and numerous continental islands. They are also important for understanding the direction evolution has taken since the ice retreated.

Even today, the region is notable for its rapid changes in sea level, which, however, have little effect on most of the coast due to the numerous fjords.

See also


  • Hidy, A. J., Gosse, J. C., Froese, D. G., Bond, J. D., and Rood, D. H. (2013). A latest Pliocene age for the earliest and most extensive Cordilleran Ice Sheet in northwestern Canada. Quaternary Science Reviews 61:77-84. [1]
  • Gwaii Haanas National Park Reserve and Haida Heritage Site
  • Clarke, T.E., D.B. Levin, D.H. Kavanaugh and T.E. Reimchen. 2001. Rapid Evolution in the Nebria Gregaria Group (Coleoptera: Carabidae) and the Paleogeography of the Queen Charlotte Islands. Evolution 51:1408–1418
  • Brown, A. S., and H. Nasmith. 1962. The glaciation of the Queen Charlotte Islands. Canadian Field-Naturalist 76:209–219.
  • Byun, S. A., B. F. Koop, and T. E. Reimchen. 1997. North American black bear mtDNA phylogeography: implications for morphology and the Haida Gwaii glacial refugium controversy. Evolution 51:1647–1653.
  • Richard B. Waitt, Jr., and Robert M. Thorson, 1983. The Cordilleran Ice Sheet in Washington, Idaho, and Montana. IN: H.E. Wright, Jr., (ed.), 1983, Late-Quaternary Environments of the United States, Volume 1: The Late Pleistocene (Stephen C. Porter (ed.)): University of Minnesota Press, 407p., Chapter 3, p.53-70. Abstract
  • Holder, K., Montgomerie, R., and V.L. Friesen. 1999. A test of the glacial refugium hypothesis using patterns of mitochondrial and nuclear DNA sequence variation in the rock ptarmingan (Lagopus mutus). Evolution 53(6):1936–1950. [2]
  • Warner, B.G., Mathewes, R.W., and J.J. Clague. 1982. Ice-free conditions on the Queen Charlotte Islands, British Columbia, at the height of late Wisconsin glaciation. Science 218(4573):675–6770. [3]
Bitter Lake (Seattle)

For the neighborhood, see Bitter Lake, Seattle.Bitter Lake is a small lake in northwest Seattle, Washington, USA.

The lake covers 19 acres (77,000 m²), with a mean depth of 16 feet (5 m) and a maximum depth of 31 feet (9 m). Until 1913, a sawmill was located at its southwest corner. Tannic acid from logs dumped into the lake gave its water a bitter taste and the lake itself a name. The Duwamish called the lake "Blackcaps on the Sides" (Lushootseed: cHálqWadee), denoting the blackcap (Rubus leucodermis) plants that grew along the shores.It is a glacial lake, its basin having been dug 15,000 years ago by the Puget Lobe of the Cordilleran Ice Sheet, which also created Lake Washington, Union, Green and Haller Lakes.The Seattle-to-Everett Interurban streetcar reached the lake in 1906, and the Bitter Lake neighborhood was annexed by Seattle in 1954.The lake is situated between Greenwood Avenue North to the west, Linden Avenue North to the east, North 137th Street to the north, and North 130th Street to the south. Bitter Lake drains through a piped outlet at its southeast end that eventually flows into Lake Union.

Boulder Park

Boulder Park National Natural Landmark, along with the nearby McNeil Canyon Haystack Rocks and Sims Corner Eskers and Kames natural landmarks, illustrate well-preserved examples of classic Pleistocene ice stagnation landforms that are found in Washington. These landforms include numerous glacial erratics and haystack rocks that occur near and on the Withrow Moraine, which is the terminal moraine of the Okanogan ice lobe.

Canadian Cascade Arc

The Canadian Cascade Arc, also called the Canadian Cascades, is the Canadian segment of the North American Cascade Volcanic Arc. Located entirely within the Canadian province of British Columbia, it extends from the Cascade Mountains in the south to the Coast Mountains in the north. Specifically, the southern end of the Canadian Cascades begin at the Canada–United States border. However, the specific boundaries of the northern end are not precisely known and the geology in this part of the volcanic arc is poorly understood. It is widely accepted by geologists that the Canadian Cascade Arc extends through the Pacific Ranges of the Coast Mountains. However, others have expressed concern that the volcanic arc possibly extends further north into the Kitimat Ranges, another subdivision of the Coast Mountains, and even as far north as Haida Gwaii (formerly known as the Queen Charlotte Islands).

Over the last 29 million years, the Canadian Cascade Arc has been erupting a chain of volcanoes along the British Columbia Coast. At least four volcanic zones in British Columbia are related to Cascade Arc volcanism. This includes a large volcanic plateau in The Interior and three linear volcanic belts on The Coast. They were formed during different geological periods, separated by millions of years, and occur in three regions referred to as the back-arc, main-arc and fore-arc. The youngest of the three belts has been sporadically active over the last 4.0–3.0 million years, with the latest eruption having taken place possibly in the last 1,000 years. About 2,350 years ago, a major explosive eruption occurred, sending a massive ash column into the atmosphere. This is recognized as the largest volcanic eruption throughout Canada within the last 10,000 years.

In historical times, the Canadian Cascade Arc has been considerably less active than the American portion of the volcanic arc. It also has no records of historical eruptions. Nevertheless, the volcanic arc poses a threat to the surrounding region. Any volcanic hazard—ranging from landslides to eruptions—could pose a significant risk to humans and wildlife. Even though there are no historical eruptions in the Canadian Cascade Arc, eruptive activity is very likely to resume; if this were to happen, relief efforts would be quickly organized. Teams such as the Interagency Volcanic Event Notification Plan (IVENP) are prepared to notify people threatened by volcanic eruptions.

Channeled Scablands

The Channeled Scablands at one time were a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods within the southeastern part of the U.S. state of Washington. The channeled scablands were scoured by more than 40 cataclysmic floods during the Last Glacial Maximum and innumerable older cataclysmic floods over the last two million years. These cataclysmic floods were repeatedly unleashed when a large glacial lake repeatedly drained and swept across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. The last of the cataclysmic floods occurred between 18,200 and 14,000 years ago.Geologist J Harlen Bretz defined "scablands" in a series of papers written in the 1920s as lowlands diversified by a multiplicity of irregular channels and rock basins eroded into basalt. Flood waters eroded the loess cover, creating large anastomizing channels that exposed bare basalt and creating butte-and-basin topography. The buttes range in height from 30 to 100 m, while the rock basins range from 10 m in width up to the 11 km long and 30 m deep Rock Lake. Bretz further stated, "The channels run uphill and downhill, they unite and they divide, they head on the back-slopes and cut through the summit; they could not be more erratically and impossibly designed."The debate on the origin of the Scablands that ensued for four decades became one of the great controversies in the history of earth science. The Scablands are also important to planetary scientists as perhaps the best terrestrial analog of the Martian outflow channels.

Dry Falls

Dry Falls is a 3.5-mile-long (5,600 m), 5.5 km in width, scalloped precipice with four major alcoves, in central Washington scablands. This cataract complex is on the opposite side of the Upper Grand Coulee from the Columbia River, and at the head of the Lower Grand Coulee, northern end of Lenore Canyon. According to the current geological model, catastrophic flooding channeled water at 65 miles per hour through the Upper Grand Coulee and over this 400-foot (120 m) rock face at the end of the last ice age. It is estimated that the falls were five times the width of Niagara, with ten times the flow of all the current rivers in the world combined.Nearly twenty thousand years ago, as glaciers moved south through North America, an ice sheet dammed the Clark Fork River near Sandpoint, Idaho. Consequently, a significant portion of western Montana flooded, forming the gigantic Lake Missoula. About the same time, Glacial Lake Columbia was formed on the ice-dammed Columbia River behind the Okanogan lobe of the Cordilleran Ice Sheet. Lake Columbia's overflow – the diverted Columbia River – drained first through Moses Coulee and as the ice dam grew, later through the Grand Coulee.

Eventually, water in Lake Missoula rose high enough to float the ice dam until it gave way, and a portion of this cataclysmic flood spilled into Glacial Lake Columbia, and then down the Grand Coulee. It is generally accepted that this process of ice-damming of the Clark Fork, refilling of Lake Missoula and subsequent cataclysmic flooding happened dozens of times over the years of the last Ice Age.This sudden flood put parts of Idaho, Washington, and Oregon under hundreds of feet of water in just a few days. These extraordinary floods greatly enlarged the Grand Coulee and Dry Falls in a short period. The large plunge pools at the base of Dry Falls were created by these floods.

Once the ice sheet that obstructed the Columbia melted, the river returned to its normal course, leaving the Grand Coulee and the falls dry. Today, this massive cliff can be viewed from the Dry Falls Interpretive Center, part of Sun Lakes-Dry Falls State Park, and located on Route 17 near the town of Coulee City. Admission is free, although a Discover Pass is required for parking.

Glacial Lake Columbia

Glacial Lake Columbia was the lake formed on the ice-dammed Columbia River behind the Okanogan lobe of the Cordilleran Ice Sheet when the lobe covered 500 square miles (1,300 km2) of the Waterville Plateau west of Grand Coulee in central Washington state during the Wisconsin glaciation. Lake Columbia was a substantially larger version of the modern-day lake behind the Grand Coulee Dam. Lake Columbia's overflow – the diverted Columbia River – drained first through Foster Coulee, and as the ice dam grew, through first Moses Coulee, and finally, the Grand Coulee.

Ice Age Floods National Geologic Trail

The Ice Age Floods National Geologic Trail or Ice Age Floods Trail is designated as the first National Geologic Trail in the United States. It will consist of a network of routes connecting facilities that will provide interpretation of the geological consequences of the Glacial Lake Missoula floods of the last glacial period that began about 110,000 years ago.

Lake Missoula

Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago. The lake measured about 7,770 square kilometres (3,000 sq mi) and contained about 2,100 cubic kilometres (500 cu mi) of water, half the volume of Lake Michigan.The Glacial Lake Missoula National Natural Landmark is located about 110 kilometres (68 mi) northwest of Missoula, Montana, at the north end of the Camas Prairie Valley, just east of Montana Highway 382 and Macfarlane Ranch. It was designated as a National Natural Landmark in 1966 because it contains the great ripples (often measuring 25 to 50 feet (7.6 to 15.2 m) high and 300 feet (91 m) long) that served as a strong supporting element for J Harlen Bretz's contention that Washington State's Channeled Scablands were formed by repeated cataclysmic floods over only about 2,000 years, rather than through the millions of years of erosion that had been previously assumed.The lake was the result of an ice dam on the Clark Fork caused by the southern encroachment of a finger of the Cordilleran Ice Sheet into the Idaho Panhandle (at the present day location of Clark Fork, Idaho, at the east end of Lake Pend Oreille). The height of the ice dam typically approached 610 metres (2,000 ft), flooding the valleys of western Montana approximately 320 kilometres (200 mi) eastward. It was the largest ice-dammed lake known to have occurred.The periodic rupturing of the ice dam resulted in the Missoula Floods – cataclysmic floods that swept across eastern Washington and down the Columbia River Gorge approximately 40 times during a 2,000 year period. The cumulative effect of the floods was to excavate 210 cubic kilometres (50 cu mi) of loess, sediment and basalt from the channeled scablands of eastern Washington and to transport it downstream. These floods are noteworthy for producing canyons and other large geologic features through cataclysms rather than through more typical gradual processes.

In addition, Middle and Early Pleistocene Missoula flood deposits have been documented to comprise parts of the glaciofluvial deposits, informally known as the Hanford formation that are found in parts of the Othello Channels, Columbia River Gorge, Channeled Scabland, Quincy Basin, Pasco Basin, and the Walla Walla Valley. The age of these deposits is demonstrated by the presence of multiple interglacial calcretes interbedded in these glaciofluvial deposits, sequences of sediments with normal and reverse magnetostratigraphy, optically stimulated luminescence dating, and unconformity truncated clastic dikes. Based upon these criteria, Quaternary geologists estimated that the oldest of the Pleistocene Missoula floods happened before 1.5 million years ago. The older Pleistocene glaciofluvial deposits within the Hanford formation are fragmentary in nature because they have been repeatedly eroded and largely removed by subsequent Missoula floods. Because of the fragmentary nature of older glaciofluvial deposits, the exact number of older Missoula floods, which are known as Ancient Cataclysmic Floods, that occurred during the Pleistocene cannot be estimated with any confidence. Although Lake Missoula likely was the source of many of the Ancient Cataclysmic Floods, the fragmentary nature of the older deposits within the Hanford formation makes precise determination of the precise origin of the floods that deposited them very difficult.

Lake Peace

Lake Peace was a post ice-age glacial lake in what is now the Peace River basin in northeastern British Columbia and northwestern Alberta. It formed approximately 14,000 BCE, after the Last Glacial Maximum, as the Laurentide Ice Sheet and Cordilleran Ice Sheet began to melt and retreat,

and may have played an important role as an easily navigatable section of an inland human migration routefrom Asia to the Americas. It remains unclear how long the lake lasted, or if it was drained in a glacial lake outburst flood, similar to the Missoula Floods that occurred on the southern margins of these same ice sheets.

Laurentide Ice Sheet

The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square kilometers, including most of Canada and a large portion of the northern United States, multiple times during the Quaternary glacial epochs, from 2.588 ± 0.005 million years ago to the present.The last advance covered most of northern North America between c. 95,000 and c. 20,000 years before the present day and, among other geomorphological effects, gouged out the five Great Lakes and the hosts of smaller lakes of the Canadian Shield. These lakes extend from the eastern Northwest Territories, through most of northern Canada, and the upper Midwestern United States (Minnesota, Wisconsin, and Michigan) to the Finger Lakes, through Lake Champlain and Lake George areas of New York, across the northern Appalachians into and through all of New England and Nova Scotia.

At times, the ice sheet's southern margin included the present-day sites of northeastern coastal towns and cities such as Boston and New York City and Great Lakes coastal cities and towns as far south as Chicago and St. Louis, Missouri, and then followed the present course of the Missouri River up to the northern slopes of the Cypress Hills, beyond which it merged with the Cordilleran Ice Sheet. The ice coverage extended approximately as far south as 38 degrees latitude mid-continent.

Nazko Cone

Nazko Cone is a small potentially active basaltic cinder cone in central British Columbia, Canada, located 75 km west of Quesnel and 150 kilometers southwest of Prince George. It is considered the easternmost volcano in the Anahim Volcanic Belt. The small tree-covered cone rises 120 m above the Chilcotin-Nechako Plateau and rests on glacial till. It was formed in three episodes of activity, the first of which took place during the Pleistocene interglacial stage about 340,000 years ago. The second stage produced a large hyaloclastite scoria mound erupted beneath the Cordilleran Ice Sheet during the Pleistocene. Its last eruption produced two small lava flows that traveled 1 km to the west, along with a blanket of volcanic ash that extends several km to the north and east of the cone.

Pacific Cordillera (Canada)

The Pacific Cordillera (Canada) is a top-level physiographic region of Canada. This cordillera is part of the North American Cordillera. The mountain ranges in this region were covered during the Pleistocene by the Cordilleran Ice Sheet. The extent of the Cordilleran ice sheet gives perspective on the geographic extent of this region, extending from coastal mountains in Alaska, south through most of the Yukon and British Columbia, bordered by the Rocky Mountains to the East, to stretch its margin beyond the Canada–United States border with five extensive lobes reaching into the mountain valleys of Montana and Washington.The Cordillera mountains were formed by the collision of tectonic plates and stray islands from the far East coast, causing the crust to buckle forming the mountains that we know today. This is the youngest of the three primary geographic regions of Canada, the others being the Canadian Shield and Great Plains. This designation is peculiar to Canada because the country's intramontane plateaus are narrow and may be considered together with adjoining ranges.

Well known mountain ranges can be found at the Pacific Cordillera, including the famous Rocky Mountain range, and the coastal mountain range stretching across British Columbia. Such places are major tourist attractions and are basis of economy for the province of British Columbia.

Rocky Prairie

Rocky Prairie is a prairie that is about 90 kilometers (56 miles) southwest of Seattle, Washington, United States of America, and about 15 kilometers (10 miles) south of Washington's capital city of Olympia.

Old Highway 99 runs through Rocky Prairie. The part of the prairie west of the highway is called West Rocky Prairie. Both the west and east sides of the prairie have various plant and animal species. Many of the plant species are flowering plants. Both sides also have areas of Mima mounds (not to be confused with the Mima mounds at Mima Mounds Natural Area Preserve about 10.5 kilometers or 6.5 miles to the west).

There are various public and private property owners who own different parts of Rocky Prairie. Some of the major land owners on the west side of the prairie are the Washington State Department of Fish and Wildlife and the Port of Tacoma. A major land owner on the east side of the prairie is Thurston County.

In West Rocky Prairie, the property that belongs to the Washington State Department of Fish and Wildlife is called the West Rocky Prairie Unit. The size of the property is 810 acres (328 hectares). Part of the property is wooded, and part of it is in the prairie. The West Rocky Prairie Unit has over 300 acres (120 hectares) of woods, 360 acres (145 hectares) of wetlands, 40 acres (15 hectares) of Quercus garryana (Garry oak trees), and 300 acres (120 hectares) of Mima Mounds.

Vashon Glaciation

The Vashon Glaciation, Vashon Stadial or Vashon Stade is a local term for the most recent period of very cold climate in which during its peak, glaciers covered the entire Puget Sound and Strait of Juan de Fuca as well as present day Seattle, Tacoma, Olympia and other surrounding areas in the western part of present day Washington (state) of the United States of America. This occurred during a cold period around the world known as the last glacial period. This was the most recent cold period of the Pleistocene Ice Age. The Pleistocene Glaciation is the ice age that the planet is currently in and has been in for the last 2.58 million years. It is the time period in which the arctic ice sheets have existed. The Pleistocene Ice Age is part of an even longer ice age called the Late Cenozoic Ice Age, which began 33.9 million years ago and is ongoing. It is the time period in which the Antarctic ice cap has existed.

The Vashon Glaciation lasted from about 19,000 - 16,000 BP (Before Present - present defined as January 1, 1950 for this scale). The Cordilleran Ice Sheet was an ice sheet that covered present-day southern Alaska and parts of western Canada. During the Vashon Glaciation, the Cordilleran Ice Sheet advanced into the Puget Sound region out of present-day British Columbia.

The Cordilleran, Laurentide, Innuitian, and the currently existing Greenland Ice Sheet all made up the North American ice sheet complex, which covered present day Canada and much of the northern U.S. This cold glaciated time for North America was called the Wisconsin glaciation. The Fraser Glaciation began when the Cordilleran Ice Sheet advanced from the mountains of British Columbia.

Volcanic history of the Northern Cordilleran Volcanic Province

The volcanic history of the Northern Cordilleran Volcanic Province presents a record of volcanic activity in northwestern British Columbia, central Yukon and the U.S. state of easternmost Alaska. The volcanic activity lies in the northern part of the Western Cordillera of the Pacific Northwest region of North America. Extensional cracking of the North American Plate in this part of North America has existed for millions of years. Continuation of this continental rifting has fed scores of volcanoes throughout the Northern Cordilleran Volcanic Province over at least the past 20 million years (see Geology of the Pacific Northwest) and occasionally continued into geologically recent times.Eruptive activity in the Northern Cordilleran Volcanic Province throughout its 20 million year history has been mainly the production of alkaline lavas, including alkaline basalts. A range of alkaline rock types not commonly found in the Western Cordillera are regionally widespread in the Northern Cordilleran Volcanic Province. These include nephelinite, basanite and peralkaline phonolite, trachyte and comendite lavas. The trachyte and comendite lavas are understood to have been created by fractionation of mainly alkali basalt magma in crustal reservoirs. An area of continental rifting, such as the Northern Cordilleran Volcanic Province, would aid the formation of high-level reservoirs of capable size and thermal activity to maintain long-lived fractionation.In the past 15 million years, at least four large volcanoes have formed their way through dense igneous and metamorphic composed bedrock of this part of North America. This includes Hoodoo Mountain, the Mount Edziza volcanic complex, Level Mountain and Heart Peaks, which are primarily located in northwestern British Columbia. Most notable of these is the 7.5 million year old Mount Edziza volcanic complex, which has had more than 20 eruptions in the past 10,000 years. The only activity present in the Northern Cordilleran Volcanic Province has been occasional earthquakes and constant boiling of hot springs. However, a high potential exists for renewed eruptive activity that could threaten life and property in the volcanic zone.

Wedgwood Rock

Wedgwood Rock is a glacial erratic (known to geologists as the Wedgwood Erratic) near the neighborhood of Wedgwood in Seattle, Washington. Its mineral composition matches that of Mount Erie, on Fidalgo Island in Skagit County, Washington, 55 mi (89 km) north. Prior to the establishment of the Wedgwood neighborhood, the erratic was known first as Lone Rock and later simply as Big Rock. Transported to its site by the Puget Lobe of the Cordilleran Ice Sheet during the Vashon Glaciation more than 14,000 years ago, it was a landmark for Native Americans in what was once a dense forest.

Today, the rock sits in a residential neighborhood on 28th Avenue NE, near NE 72nd Street, still surrounded by trees and brush, and kept clear by local residents.

Wisconsin glaciation

The Wisconsin Glacial Episode, also called the Wisconsinan glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cordillera; the Innuitian ice sheet, which extended across the Canadian Arctic Archipelago; the Greenland ice sheet; and the massive Laurentide ice sheet, which covered the high latitudes of central and eastern North America. This advance was synchronous with global glaciation during the last glacial period, including the North American alpine glacier advance, known as the Pinedale glaciation. The Wisconsin glaciation extended from approximately 75,000 to 11,000 years ago, between the Sangamonian Stage (known globally as the Eemian stage) and the current interglacial, the Holocene. The maximum ice extent occurred approximately 25,000–21,000 years ago during the last glacial maximum, also known as the Late Wisconsin in North America.

This glaciation radically altered the geography north of the Ohio River. At the height of the Wisconsin Episode glaciation, the ice sheet covered most of Canada, the Upper Midwest, and New England, as well as parts of Idaho, Montana, and Washington. On Kelleys Island in Lake Erie or in New York City's Central Park, the grooves left in rock by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, North America's northernmost point that remained south of the continental ice sheets. During much of the glaciation, sea level was low enough to permit land animals, including humans, to occupy Beringia (the Bering Land Bridge) and move between North America and Siberia. As the glaciers retreated, glacial lakes were breached in great floods of water such as the Kankakee Torrent, which reshaped the landscape south of modern Chicago as far as the Ohio and Mississippi Rivers.

Withrow, Washington

Withrow is an unincorporated community in Douglas County, Washington, United States.Named for a cattleman named J.J. Withrow, Withrow lies at the base of the Withrow Moraine and Jameson Lake Drumlin Field is a National Park Service designated privately owned National Natural Landmark located in Douglas County, Washington state, United States. Withrow Moraine is the only Ice Age terminal moraine on the Waterville Plateau section of the Columbia Plateau. It lies on the terminal moraine for the Okanogan lobe of the Cordilleran Ice Sheet, which flowed southward through the Okanogan trough from the Interior Plateau of British Columbia blocking the course of the Columbia River and ending on the elevations of the Waterville Plateau.

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