Mountain Ranges, Deserts and Landforms of United States

Geography

The Rocky Mountains are the easternmost portion of the expansive North American Cordillera. They are often defined as a network stretching from the Liard River in British Columbia south to the headwaters of the Pecos River, a tributary of the Rio Grande, in New Mexico. The Rockies vary in width from 110 to 480 kilometers (70 to 300 miles). The greater Rocky Mountain system functions as a collective network of dozens of distinct subranges divided by high basins and wide rolling tablelands. The Rocky Mountains contain the highest peaks in central North America. The range's highest peak is Mount Elbert in Colorado at 4,401 meters (14,440 feet) above sea level. Mount Robson in British Columbia, at 3,954 m (12,972 ft), is the highest peak in the Canadian Rockies.

Geology

The rocks in the Rocky Mountains were formed before the mountains were raised by tectonic forces. The oldest rock is Precambrian metamorphic rock that forms the core of the North American continent. There is also Precambrian sedimentary argillite, dating back to 1.7 billion years ago. During the Paleozoic, western North America lay underneath a shallow sea, which deposited many kilometers of limestone and dolomite.

In the southern Rockies, near present-day Colorado, these ancestral rocks were disturbed by mountain building approximately 300 million years ago, during the Pennsylvanian. This mountain-building produced the Ancestral Rocky Mountains. They consisted largely of Precambrian metamorphic rock forced upward through layers of the limestone laid down in the shallow sea.

Ecology and climate

There are a wide range of environmental factors in the Rocky Mountains. The Rockies range in latitude between the Liard River in British Columbia (at 59° N) and the Rio Grande in New Mexico (at 35° N). Prairie occurs at or below 550 meters (1,800 ft), while the highest peak in the range is Mount Elbert at 4,400 meters (14,440 ft). Precipitation ranges from 250 millimeters (10 in) per year in the southern valleys to 1,500 millimeters (60 in) per year locally in the northern peaks. Average January temperatures can range from −7 °C (20 °F) in Prince George, British Columbia, to 6 °C (43 °F) in Trinidad, Colorado. Therefore, there is no single monolithic ecosystem for the entire Rocky Mountain Range.

Instead, ecologists divide the Rockies into a number of biotic zones.

History

Since the last great ice age, the Rocky Mountains were home first to indigenous peoples including the Apache, Arapaho, Bannock, Blackfoot, Cheyenne, Coeur d'Alene, Kalispel, Crow Nation, Flathead, Shoshone, Sioux, Ute, Kutenai (Ktunaxa in Canada), Sekani, Dunne-za, and others. Paleo-Indians hunted the now-extinct mammoth and ancient bison (an animal 20% larger than modern bison) in the foothills and valleys of the mountains.

Geography

The Great Basin physiographic section of the Basin and Range Province contains the Great Basin, but extends into eastern Oregon, southern Idaho, and the Colorado River watershed and the northwest corner of Arizona. The Basin and Range region is the product of geological forces stretching the Earth's crust, creating many north–south trending mountain ranges. These ranges are separated by flat valleys or basins. These hundreds of ranges make Nevada the most mountainous state in the country.

The Great Basin's two most populous metropolitan areas are the Reno-Sparks metropolitan area to the west and the Salt Lake City centered Wasatch Front to the east (with the latter being significantly more populous than the former).

Geology

The Great Basin includes valleys, basins, lakes and mountain ranges of the Basin and Range Province.

The basin and range topography is the result of extension and thinning of the lithosphere, which is composed of crust and upper mantle. Extensional environments like the Basin and Range are characterized by listric normal faulting, or faults that level out with depth. Opposing normal faults link at depth producing a horst and graben geometry, where horst refers to the upthrown fault block and graben to the down dropped fault block.

Sediment build-up over thousands of years filled the down-faulted basins between ranges and created relatively flat lacustrine plains from Pleistocene lake beds of the Great Basin.

Climate

The climate varies throughout the Great Basin by elevation, latitude, and other factors. Higher elevations tend to be cooler and receive more precipitation. The western areas of the basin tend to be drier than the eastern areas because of the rain shadow of the Sierra Nevada. Most of the basin experiences a semi-arid or arid climate with warm summers and cold winters. However, some of the mountainous areas in the basin are high enough in elevation to experience an alpine climate. Due to the region's altitude and aridity, most areas in the Great Basin experience a substantial diurnal temperature variation.

Ecology

The hydrographic Great Basin contains multiple deserts and ecoregions, each with its own distinctive set of flora and fauna. The ecological boundaries and divisions in the Great Basin are unclear.

The Great Basin overlaps four different deserts: portions of the hot Mojave and Colorado (a region within the Sonoran Desert) Deserts to the south, and the cold Great Basin and Oregon High Deserts in the north. The deserts can be distinguished by their plants: the Joshua tree and creosote bush occur in the hot deserts, while the cold deserts have neither. The cold deserts are generally higher than the hot and have more even spread of precipitation throughout the year.

Geography

There are several larger mountain ranges in the Chihuahuan Desert, including the Sierra Madre, the Sierra del Carmen, the Organ Mountains, the Franklin Mountains, the Sacramento Mountains, the Chisos Mountains, the Guadalupe Mountains, and the Davis Mountains. These create "sky islands" of cooler, wetter, climates adjacent to, or within the desert, and such elevated areas have both coniferous and broadleaf woodlands, including forests along drainages and favored exposures. The lower elevations of the Sandia–Manzano Mountains, the Magdalena–San Mateo Mountains, and the Gila Region partly border the Chihuahuan Desert and partly border other ecoregions that are not deserts.

Climate

The desert is mainly a rain shadow desert because the two main mountain ranges which bound the desert, the Sierra Madre Occidental to the west and the Sierra Madre Oriental to the east, block most moisture from the Pacific Ocean and the Gulf of Mexico, respectively. Climatically, the desert mostly has an arid, mesothermal climate with one rainy season in the late summer and smaller amounts of precipitation in early winter, the mean daily temperature of the coldest month warmer than 0 °C (32 °F). The majority of rain falls between late June and early October during the North American Monsoon, when moist air from the Gulf of Mexico and the Sea of Cortez penetrates into the region, or much less frequently, when a tropical cyclone moves inland and stalls.

Geography

This province is bounded by the Rocky Mountains in Colorado and by the Uinta Mountains and Wasatch Mountains branches of the Rockies in northern and central Utah. It is also bounded by the Rio Grande rift, Mogollon Rim, and the Basin and Range Province (at the Hurricane Fault). Isolated ranges of the Southern Rocky Mountains, such as the San Juan Mountains in Colorado and the La Sal Mountains in Utah, intermix into the central and southern parts of the Colorado Plateau.

As the name implies, the High Plateaus Section is, on average, the highest section. North-south trending normal faults that include the Hurricane, Sevier, Grand Wash, and Paunsaugunt separate the section's component plateaus.

Geology

One of the most geologically intriguing features of the Colorado Plateau is its remarkable stability. Relatively little rock deformation such as faulting and folding has affected this high, thick crustal block within the last 600 million years or so, although there are some newer features such as the Waterpocket Fold of Capitol Reef (estimated 50–70 million years old). In contrast, provinces that have suffered severe deformation surround the plateau. Mountain building thrust up the Rocky Mountains to the north and east and tremendous, earth-stretching tension produced the Basin and Range Province to the west and south. Sub ranges of the Southern Rocky Mountains are scattered throughout the Colorado Plateau.

Human history

The Ancestral Puebloan People lived in the region from roughly 2000 to 700 years ago. A party from Santa Fe led by Fathers Dominguez and Escalante, unsuccessfully seeking an overland route to California, made a five-month out-and-back trip through much of the Plateau in 1776–1777. Despite having lost one arm in the American Civil War, U.S. Army Major and geologist John Wesley Powell explored the area in 1869 and 1872. Using wooden oak boats and small groups of men, the Powell Geographic Expedition charted this largely unknown region of the United States for the federal government.

Construction of the Hoover Dam in the 1930s and the Glen Canyon Dam in the 1960s changed the character of the Colorado River.

Climate

The Sonoran desert has an arid subtropical climate and is considered to be the most tropical desert in North America. In the lower-elevation portions of the desert, temperatures are warm year-round, and rainfall is infrequent and irregular, often less than 90 mm (approx. 3.5") annually. The Arizona uplands are also warm year-round, but they receive 100–300 mm (approx. 4–12") of average annual rainfall, which falls in a more regular bi-seasonal pattern.

According to the Köppen climate classification system, the majority of the Sonoran Desert has a hot desert climate (BWh).

Location

The Sonoran desert wraps around the northern end of the Gulf of California, from Baja California Sur (El Vizcaíno Biosphere Reserve in central and Pacific west coast, Central Gulf Coast subregion on east to southern tip), north through much of Baja California, excluding the central northwest mountains and Pacific west coast, through southeastern California and southwestern and southern Arizona to western and central parts of Sonora.

It is bounded on the west by the Peninsular Ranges, which separate it from the California chaparral and woodlands (northwest) and Baja California desert (Vizcaíno subregion, central and southeast) ecoregions of the Pacific slope.

Geography

The Coast Mountains consists of three subdivisions known as the Pacific Ranges, the Kitimat Ranges, and the Boundary Ranges. The Pacific Ranges are the southernmost subdivision of the Coast Mountains, extending from the lower stretches of the Fraser River to Bella Coola. Included in this subdivision are four of the five major coastal icecaps in the southern Coast Mountains. These are the largest temperate-latitude icecaps in the world and fuel a number of major rivers. Other than logging and a large ski resort at the resort town of Whistler, most of the land in the range is completely undeveloped. Mount Waddington, the highest mountain of the Coast Mountains, lies in the Waddington Range of the Pacific Ranges.

Geology

The Coast Mountains consist of deformed igneous and metamorphosed structurally complex pre-Tertiary rocks. These originated in diverse locations around the globe: the area is built of several different terranes of different ages with a broad range of tectonic origins. In addition, oceanic crust under the Pacific Ocean is being subducted at the southern portion of the range to form a north–south line of volcanoes called the Garibaldi Volcanic Belt, a northern extension of the Cascade Volcanoes in the northwestern United States, and contains the most explosive young volcanoes in Canada. Further north the northwesterly structural trend of the Coast Mountains lies partly in a large continental rift responsible for the creation of several volcanoes.

Geography

The Cascades extend northward from Lassen Peak (also known as Mount Lassen) in northern California to the confluence of the Nicola and Thompson rivers in British Columbia. The Fraser River separates the Cascades from the Coast Mountains in Canada, as does the Willamette Valley from the upper portion of the Oregon Coast Range. The highest volcanoes of the Cascades, known as the High Cascades, dominate their surroundings, often standing twice the height of the nearby mountains. They often have a visual height (height above nearby crestlines) of one mile or more. The highest peaks, such as the 14,411-foot (4,392 m) Mount Rainier, dominate their surroundings for 50 to 100 miles (80 to 161 km).

Geology

The Cascade Range is made up of a band of thousands of very small, short-lived volcanoes that have built a platform of lava and volcanic debris. Rising above this volcanic platform are a few strikingly large volcanoes, like Mount Hood and Mount St. Helens, that dominate the landscape.

The Cascade volcanoes define the Pacific Northwest section of the Ring of Fire, an array of volcanoes that rim the Pacific Ocean. The Ring of Fire is also known for its frequent earthquakes. The volcanoes and earthquakes arise from a common source, namely subduction. In this case, the dense Juan de Fuca Plate plunges beneath the North American Plate at the Cascadia subduction zone.

Ecology

Forests of large, coniferous trees (western red cedars, Douglas-firs, western hemlocks, firs, pines, spruces, and others) dominate most of the Cascade Range. Cool, wet winters and warm, dry summers (largely a result of oceanic influence) favor evergreen species, whereas mild temperatures and rich soils promote fast and prolonged growth.

As a traveler passes through the Cascade Range, the climate first gets colder, then warmer and drier east of the crest. Most of the Cascades' lower and middle elevations are covered in coniferous forest; the higher altitudes have extensive meadows as well as alpine tundra and glaciers. The southern part of the Cascades are within the California Floristic Province, an area of high biodiversity.

History

Before European exploration, First Nations tribes named many peaks, including "Seekseekqua" for Mount Jefferson (Oregon), "M'laiksini Yaina" for Mount McLoughlin, "Tahoma", the Lushootseed name for Mount Rainier, and "Louwala-Clough", meaning "smoking mountain" for Mount St. Helens.

In early 1792, British navigator George Vancouver explored Puget Sound and gave English names to the high mountains he saw. Mount Baker was named for Vancouver's third lieutenant, Joseph Baker, although the first European to see it was Manuel Quimper, who named it la gran montaña del Carmelo ("Great Mount Carmel") in 1790. Mount Rainier was named after Admiral Peter Rainier.

History

The name "Alaskan Range" appears to have been first applied to these mountains in 1869 by naturalist W. H. Dall. The name eventually became "Alaska Range" through local use. In 1849 Constantin Grewingk applied the name "Tschigmit" to this mountain range. A map made by the United States General Land Office in 1869 calls the southwestern part of the Alaska Range the "Chigmit Mountains" and the northeastern part the "Beaver Mountains". However, the Chigmit Mountains are now considered part of the Aleutian Range.

Starting in the mid-1880s to early 1900s, early non-native explorers traversed various sections of the Alaska Range. The first recorded expedition was in the Eastern Alaska Range led by H. T. Allen in 1885.

Description

The range forms a generally east–west arc with its northernmost part in the center, and from there trending southwest towards the Alaska Peninsula and the Aleutian Islands, and trending southeast into British Columbia and the Pacific Coast Ranges. The mountains act as a high barrier to the flow of moist air from the Gulf of Alaska northwards, and thus have some of the harshest weather in the world. The heavy snowfall also contributes to a number of large glaciers, including the Cantwell, Castner, Black Rapids, Susitna, Yanert, Muldrow, Eldridge, Ruth, Tokositna, and Kahiltna Glaciers. Four major rivers cross the Alaska Range, including the Delta and Nenana Rivers in the center of the range and the Nabesna and Chisana Rivers to the east.

Geography

The Sierra Nevada lies primarily in Central and Eastern California, with the Carson Range, a small but historically important spur, extending into Nevada. West-to-east, the Sierra Nevada's elevation increases gradually from 500 feet (150 m) in the Central Valley to more than 14,000 feet (4,300 m) atop the highest peaks of its crest 50 to 75 miles (80 to 121 km) to the east. The east slope forms the steep Sierra Escarpment. Unlike its surroundings, the range receives a substantial amount of snowfall and precipitation due to orographic lift.

The Sierra Nevada's irregular northern boundary stretches from the Susan River and Fredonyer Pass to the North Fork Feather River.

Climate and meteorology

The climate of the Sierra Nevada is influenced by the Mediterranean climate of California. During the fall, winter and spring, precipitation in the Sierra ranges from 20 to 80 in (510 to 2,030 mm) where it occurs mostly as snow above 6,000 ft (1,800 m). Precipitation is highest on the central and northern portions of the western slope between 5,000 and 8,000 feet (1,500 and 2,400 m) elevation, due to orographic lift. Above 8,000 feet (2,400 m), precipitation diminishes on the western slope up to the crest, since most of the precipitation has been wrung out at lower elevations. Most parts of the range east of the crest are in a rain shadow, and receive less than 25 inches of precipitation per year.

Ecology

The western foothill zone, 1,000–2,500 ft (300–760 m), with grassland, oak-grass savanna and chaparral-oak woodland. Gray pine (also known as Foothill pine) is intermixed with the oak woodland.

The Pinyon pine-Juniper woodland, 5,000–7,000 ft (1,500–2,100 m) east side only.

The Sierra Nevada lower montane forest (indicator species: Ponderosa pine, Jeffrey pine), 2,500–7,000 ft (760–2,130 m) west side, 7,000–9,000 ft (2,100–2,700 m) east side. This biotic zone is notable for containing giant sequoia.

The Sierra Nevada upper montane forest (indicator species: Lodgepole pine, Red fir) 7,000–9,000 ft (2,100–2,700 m) west side, 9,000–10,500 ft (2,700–3,200 m) east side.

The alpine region at greater than 10,500 ft (3,200 m), and greater than 11,500 ft (3,500 m) east side.

History

Archaeological excavations placed Martis people of Paleo-Indians in northcentral Sierra Nevada during the period of 3,000 BCE to 500 CE. The earliest identified sustaining indigenous people in the Sierra Nevada were the Northern Paiute tribes on the east side, with the Mono tribe and Sierra Miwok tribe on the western side, and the Kawaiisu and Tübatulabal tribes in the southern Sierra. Today, some historic intertribal trade route trails over mountain passes are known artifact locations, such as Duck Pass with its obsidian arrowheads.

Geography

The base of the Alaska Peninsula extends outward from the end of the Alaska Range.

The Aleutian Range is a very active volcanic mountain range which runs along the entire length of the peninsula. Within it lie Wildlife Refuges, including the Katmai National Park and Preserve, the Aniakchak National Monument and Preserve and the Becharof National Wildlife Refuge, the Alaska Peninsula National Wildlife Refuge, and the Izembek National Wildlife Refuge. The most active volcano along the volcanic mountain range is Pavlof Volcano which is more than 8,251 feet (2,515 meters)(see also: Aleutian Arc).

Climate

Average annual precipitation ranges from 24–65 in (610–1,650 mm). Coastal areas are subject to intense storms, wind, and rain. Winter temperatures average between 12 and 34 °F (−11 and 1 °C), and in summer between 43 and 59 °F (6 and 15 °C). Frosts can occur any day of the year at higher elevations. The climate can be compared to that of parts of Scotland, the Aleutian Islands, Iceland, and Tierra del Fuego.

Geography

Although the term "Blue Ridge" is sometimes applied exclusively to the eastern edge or front range of the Appalachian Mountains, the geological definition of the Blue Ridge province extends westward to the Ridge and Valley area, encompassing the Great Smoky Mountains, the Great Balsams, the Roans, the Blacks, and other mountain ranges. In North Carolina, two lower elevation ranges to the east, referred to as foothills, are also often included as "spurs" of the Blue Ridge: the Brushy Mountains and the South Mountains. In Virginia, the Southwest Mountains are an anticlinal range that similarly parallels the Blue Ridge.

The Blue Ridge extends as far south as Mount Oglethorpe in Georgia and as far north into Pennsylvania as South Mountain.

Geology

Most of the rocks that form the Blue Ridge Mountains are ancient granitic charnockites, metamorphosed volcanic formations, and sedimentary limestone. Recent studies completed by Richard Tollo, a professor and geologist at George Washington University, provide greater insight into the petrologic and geochronologic history of the Blue Ridge basement suites. Modern studies have found that the basement geology of the Blue Ridge is made of compositionally unique gneisses and granitoids, including orthopyroxene-bearing charnockites. Analysis of zircon minerals in the granite completed by John Aleinikoff at the U.S. Geological Survey has provided more detailed emplacement ages.

History

Native American nations including the Siouan Manahoacs, the Haudenosaunee Confederacy, and the Shawnee hunted and fished at the foot of the Blue Ridge Mountain Range before colonial contact. A German physician-explorer, John Lederer, first reached the crest of the Blue Ridge in 1669 and again the following year; he also recorded the Virginia Siouan name for the Blue Ridge (Ahkonshuck).

At the Treaty of Albany negotiated by Virginia Lieutenant Governor Alexander Spotswood with the Haudenosaunee between 1718 and 1722, the Haudenosaunee ceded lands they had conquered south of the Potomac River and east of the Blue Ridge to the Virginia Colony.

Geography and ecology

The Seward Peninsula has several distinct geologic features. The Devil Mountain Lakes on the northern portion of the peninsula are the largest maar lakes in the world and part of the Espenberg volcanic field. They were formed over 21,000 years ago as the result of an underground steam explosion. The Killeak Lakes and White Fish Lake are also volcanic maar lakes of notable size on the northern Seward Peninsula. Four mountain ranges line the southern side of the peninsula, the most prominent being the Kigluaik (or Sawtooth) Mountains. The highest point in the range and the peninsula is the peak of 4,714 ft (1,437 m) Mount Osborn. Other mountain ranges on the Seward Peninsula include the Bendeleben Mountains, Darby Mountains, and York Mountains.

Geography

The Ouachitas are a major physiographic province of Arkansas and Oklahoma and are generally grouped with the Arkansas River Valley. Together with the Ozark Plateaus, the Ouachitas form the U.S. Interior Highlands, one of few mountainous regions between the Appalachians and Rockies.

The Ouachitas are dominated by pine, oak, and hickory. The shortleaf pine (Pinus echinata) and post oak (Quercus stellata) thrive in dry, nutrient-poor soil and are common in upland areas. The maple-leaf oak (Quercus acerifolia) is found at only four sites worldwide, all of which are in the Ouachitas. Some native tree species, such as the eastern red-cedar (Juniperus virginiana), are colonizers of human-disturbed sites.

The Ouachita National Forest covers approximately 1.8 million acres of the Ouachitas.

Geology

The Ouachitas are formed by a thick succession of highly deformed Paleozoic strata constituting the Ouachita Fold and Thrust Belt, which crops out for approximately 220 miles (350 km) in western Arkansas and southeastern Oklahoma. In a general sense, the Ouachitas are considered an anticlinorium because the oldest known rocks are located towards the center of the outcrop area. The Ouachitas continue in the subsurface to the Black Warrior Basin of Alabama and Mississippi where they plunge towards the Appalachian Mountains. To the southwest, the Ouachitas join with the Marathon area of west Texas where rocks of the Ouachita Fold and Thrust Belt are briefly exposed.

Unlike many ranges in the United States, the Ouachitas are mostly east-west trending.

History

The mountains were home to the Ouachita tribe, for which they were named. Later French explorers translated the name to its present spelling. The first recorded exploration was in 1541 by Hernando de Soto. Later, in 1804, President Jefferson sent William Dunbar and Dr. George Hunter to the area after the Louisiana Purchase. Hot Springs National Park became one of the nation's first parks in 1832. The Battle of Devil's Backbone was fought here at the ridge of the same name in 1863. In August 1990, the U.S. Forest Service discontinued clearcutting as the primary tool for harvesting and regenerating short leaf, pine and hardwood forests in the Ouachita National Forest.

Tourism

The Ouachita Mountains contain the Ouachita National Forest, Hot Springs National Park and Lake Ouachita, as well as numerous state parks and scenic byways mostly throughout Arkansas. They also contain the Ouachita National Recreation Trail, a 223-mile-long (359 km) hiking trail through the heart of the mountains. The trail runs from Talimena State Park in Oklahoma to Pinnacle Mountain State Park near Little Rock. It is a well maintained, premier trail for hikers, backpackers, and mountain bikers (for only selected parts of the trail).

History

1805, the Corps of Discovery, led by Meriwether Lewis and William Clark and aided by Sacajawea of the Shoshone tribe, crossed the Bitterroot Range several times. Lewis first crossed the mountains at Lemhi Pass on August 12, then returned across the pass to meet Clark. The entire expedition then crossed the pass to the Salmon River valley, and the next month entered the Bitterroot Valley from the south via either Lost Trail Pass or Chief Joseph Pass. It then crossed Lolo Pass to the west. In June 1806 the Corps of Discovery was then led by 5 members of the Nez Percé back across the Bitterroot Range, from west to east. The Bitterroots also presented a massive problem for the expedition, ending their hope of finding an all water Northwest Passage.

Geography

Though the five lakes lie in separate basins, they form a single, naturally interconnected body of fresh water, within the Great Lakes Basin. As a chain of lakes and rivers, they connect the east-central interior of North America to the Atlantic Ocean. From the interior to the outlet at the Saint Lawrence River, water flows from Superior to Huron and Michigan, southward to Erie, and finally northward to Lake Ontario. The lakes drain a large watershed via many rivers and contain approximately 35,000 islands. There are also several thousand smaller lakes, often called "inland lakes", within the basin.

Geology

It has been estimated that the foundational geology that created the conditions shaping the present day upper Great Lakes was laid from 1.1 to 1.2 billion years ago, when two previously fused tectonic plates split apart and created the Midcontinent Rift, which crossed the Great Lakes Tectonic Zone. A valley was formed providing a basin that eventually became modern day Lake Superior. When a second fault line, the Saint Lawrence rift, formed approximately 570 million years ago, the basis for Lakes Ontario and Erie was created, along with what would become the Saint Lawrence River.

The Great Lakes are estimated to have been formed at the end of the Last Glacial Period (the Wisconsin glaciation ended 10,000 to 12,000 years ago), when the Laurentide Ice Sheet receded.

Climate

Köppen climate classification Dfa (in southern areas) and Dfb (in northern parts) with varying influences from air masses from other regions including dry, cold Arctic systems, mild Pacific air masses from the west, and warm, wet tropical systems from the south and the Gulf of Mexico. The lakes have a moderating effect on the climate; they can also increase precipitation totals and produce lake effect snowfall.

The Great Lakes can have an effect on regional weather called lake-effect snow, which is sometimes very localized. Even late in winter, the lakes often have no icepack in the middle. The prevailing winds from the west pick up the air and moisture from the lake surface, which is slightly warmer in relation to the cold surface winds above.

Ecology

Historically, the Great Lakes, in addition to their lake ecology, were surrounded by various forest ecoregions (except in a relatively small area of southeast Lake Michigan where savanna or prairie occasionally intruded). Logging, urbanization, and agriculture uses have changed that relationship. In the early 21st century, Lake Superior's shores are 91% forested, Lake Huron 68%, Lake Ontario 49%, Lake Michigan 41%, and Lake Erie, where logging and urbanization has been most extensive, 21%. Some of these forests are second or third growth (i.e. they have been logged before, changing their composition).

Geology

About 1 billion years ago, a mass of magma rose to the surface through a much older mantle, cooling to form what is now known as the Precambrian Pikes Peak Granite. Over the next 500 million years, the granite eroded with no sedimentation forming over this first uplift, resulting in a local expression of the Great Unconformity. At about 500–300 million years ago, the region began to sink and sediments began to deposit in the newly formed accommodation space. Eroded granite produced sand particles that began to form strata, layers of sediment, in the sinking basin. Sedimentation would continue to take place until about 300 million years ago.

Geography

The peninsula extends about 150 miles (240 km) southwest from the Chugach Mountains, south of Anchorage. It is separated from the mainland on the west by Cook Inlet and on the east by Prince William Sound. Most of the peninsula is part of the Kenai Peninsula Borough. Athabaskan and Alutiiq Native groups lived on the peninsula for thousands of years prior to colonization during the Russian America era.

The glacier-covered Kenai Mountains run along the southeast spine of the peninsula along the coast of the Gulf of Alaska. Much of the range is within Kenai Fjords National Park. The northwest coast along the Cook Inlet is flatter, dotted with numerous small lakes. Several larger lakes extend through the interior of the peninsula, including Skilak Lake and Tustumena Lake.

Natural resources and economy

The peninsula also has natural gas, petroleum, and coal deposits, as well as abundant commercial and personal-use fisheries. Tourism is a major industry, along with outfitting and guiding services for hunters and fishers. The Kenai Peninsula is known as "Alaska's Playground". Kenai National Wildlife Refuge encompasses nearly two million acres of the peninsula.

Description

The Rim is an escarpment defining the southwestern edge of the Colorado Plateau. Its central and most spectacular portions are characterized by high cliffs of limestone and sandstone, namely the Kaibab Limestone and Coconino Sandstone cliffs. The escarpment was created by erosion and faulting, creating canyons such as Fossil Creek Canyon and Pine Canyon. The name Mogollon comes from Don Juan Ignacio Flores Mogollón, the Spanish Governor of New Mexico from 1712 to 1715.

Much of the land south of the Mogollon Rim lies 4,000 to 5,000 feet (1,200 to 1,500 m) above sea level, with the escarpment rising to about 8,000 ft (2,400 m). Extensive Ponderosa pine forests are found both on the slopes of the Rim and on the plateau to the north.

Hydrology

The Mogollon rim drains an extensive area, and has numerous springs and creeks (perennial and intermittent) draining from it. The Verde Valley alone may have more than 820 natural springs, many of which originate from surface precipitation and subsurface waters of the Mogollon rim. Springs along the Mogollon rim can occur in almost all local rock types and the ground water flow system may be highly complex and spring water flow may be highly variable. Average annual precipitation along the Mogollon rim is also somewhat variable by location and elevation, some high areas along the edge of the rim and in high elevation canyons may receive in excess of 30-35 inches (762-889mm) of annual precipitation.

Geography

The range lies north of Dawson City, and is crossed by the Dempster Highway.

The area was first surveyed by William Ogilvie and the range subsequently named after him.

The best known mountain peaks of the Ogilvie Mountains are located within Tombstone Territorial Park.

The highest mountain within the range is Mount Frank Rae, at 2,362 m (7,749 ft) in elevation.

Geology

The geology of the Black Hills is complex. A Tertiary mountain-building episode is responsible for the uplift and current topography of the Black Hills region. This uplift was marked by volcanic activity in the northern Black Hills. The southern Black Hills are characterized by Precambrian granite, pegmatite, and metamorphic rocks that comprise the core of the entire Black Hills uplift. This core is rimmed by Paleozoic, Mesozoic, and Cenozoic sedimentary rocks. The stratigraphy of the Black Hills is laid out like a target, as it is an oval dome, with rings of different rock types dipping away from the center.

The 'bull's eye' of this target is called the granite core.

History

Although the written history of the region begins with the Sioux domination of the land over the native Arikara tribes, researchers have carbon-dating and stratigraphic records to analyze the early history of the area. Scientists have been able to utilize carbon-dating to evaluate the age of tools found in the area, which indicate a human presence that dates as far back as 11,500 BC with the Clovis culture.

The Black Hills have been inhabited by numerous indigenous groups over the centuries. The Ponca, Arikara, and Mandan were among the earliest recorded inhabitants, and were later displaced by the Kiowa, Plains Apache, and Shoshone. Those groups had largely left the area by around 1800 and returned only occasionally for trading or raids on other groups.

Tourism and economy

The region is home to Mount Rushmore National Memorial, Wind Cave National Park, Jewel Cave National Monument, Black Elk Peak, Custer State Park (the largest state park in South Dakota, and one of the largest in the US), Bear Butte State Park, Devils Tower National Monument, and the Crazy Horse Memorial. The Black Hills also hosts the Sturgis Motorcycle Rally each August. The rally was started in 1940 and the 65th Rally in 2005 saw more than 550,000 bikers visit the Black Hills. It is a key part of the regional economy.

The South Dakota Centennial Trail is a hiking and mountain biking trail which opened in 1989 to celebrate the 100th anniversary of South Dakota becoming a state.

Climate

The Great Salt Lake Desert experiences a desert climate with hot summers and cold winters. The desert is an excellent example of a cold desert climate. The elevation, 4,250 feet above sea level, makes temperatures cooler than lower elevation deserts, such as the Mojave. The high elevation and aridity cause temperatures to drop sharply after sunset. Summer nights are comfortably cool. Winter highs are generally above freezing, and winter nights are cold, with temperatures often dropping below freezing.

History

During Jedediah Smith's 1826-27 expedition, Robert Evans nearly died while crossing the desert, and in the 1840s, westward emigrants used the Hastings Cutoff through 130 miles (210 km) of Great Salt Lake desert to reduce the distance to California. The 1846 Donner Party's difficulties in making the crossing contributed to their becoming snowbound in the Sierra Nevada. Howard Stansbury explored the desert in 1849. In 1956, I-80 replaced the Wendover Cut-off across the desert, including a straight east-west section for ~50 miles (80 km) between the Cedar Mountains to the east and Wendover on the Utah/Nevada border. Following a railway completed across the Bonneville Salt Flats in 1910, the flats were first used as a speedway in 1914.

Description

Several small mountain ranges occupy the edges of the desert, such as the Cedar Mountains, Lakeside Mountains, Silver Island Mountains, Hogup Mountains, Grassy Mountains, and Newfoundland Mountains. On the western edge of the desert, just across the border in Nevada, stands Pilot Peak in the Pilot Range.

The desert is cool during the winter and includes unusual plants adapted to the dry conditions. Most of the desert receives less than 8 inches (200 mm) of annual precipitation. The salt crust covering the desert reforms yearly when the rain evaporates. The military's Utah Test and Training Range is in the northern portion of the desert.

Geography and climate

The Llano Estacado lies at the southern end of the Western High Plains ecoregion of the Great Plains of North America; it is part of what was once called the Great American Desert. The Canadian River forms the Llano's northern boundary, separating it from the rest of the High Plains. To the east, the Caprock Escarpment, a precipitous cliff about 300 feet (100 m) high, lies between the Llano and the red Permian plains of Texas; while to the west, the Mescalero Ridge demarcates the eastern edge of the Pecos River valley. The Llano has no distinct southern boundary, instead blending into the Edwards Plateau near Big Spring, Texas.

Geology

When the weather is dry, they are dusty, round, gray, usually unvegetated flats, as observed from the highway. But after a High Plains thunderstorm, water quickly fills the ponds, only later soaking into the underlying porous sandstones just below the surface to add to the groundwater in the Ogallala aquifer. Early pioneers depended dearly on water from these surface ponds for themselves and their livestock, considering how few streams are on the High Plains. But rains didn't always come, and the ponds dried up frequently. The 20th century has witnessed a concerted effort to tap the more reliable Ogallala water sands.

History

In the early 18th century, the Comanches expanded their territory into the Llano Estacado, displacing the Apaches who had previously lived there. The region became part of the Comancheria, a Comanche stronghold until the final defeat of the tribe in the late 19th century. The Comanche war trail extended from Llano Estacado to the Rio Grande into Chihuahua, "the trail ran southwesterly through Big Spring to the Horsehead Crossing of the Pecos River, then forked southward to the Comanche Springs where it divided, one part of the trail crossing the great river near Boquillas and the other at Presidio."

Rachel Plummer, while a captive of the Comanche in 1836, mentioned the "table lands between Austin and Santa Fe".

Economy

The economy of the Llano Estacado is predominantly agricultural, with farming of various crops prevalent, as is cattle ranching. Oil and gas production is also intense throughout the Llano Estacado making it one of the most productive petrochemical areas in the United States.

Overuse of the aquifer in the past has persuaded some farmers to return to dryland crops, leading to less rainwater reaching the playas.

"Cotton, grain sorghum, corn, wheat, peanuts, sunflowers, grapes, vegetables, and cattle produced in the region literally go around the world. Their economic impact on our area is in the billions of dollars... and the availability of water is a key factor influencing the region's agribusiness economy."

History

This glacier was advancing in 1890 when viewed by John Muir, and had a large calving front. By 1963, the glacier had advanced 5.6 km (3.5 mi). In 1948, the Taku Fjord had been completely filled in with glacial sediment and the glacier no longer calved. From 1948–1986, the glacier had a positive glacier mass balance driving the advance. From 1987–2009, the glacier has had a slightly negative mass balance, not enough to end the advance, but if it continues will soon slow it.

The icefield, like many of its glaciers, reached its maximum glaciation point around 1700 and has been in retreat since. Much of the icefield is contained within the Tongass National Forest. Since 1948, the Juneau Icefield Research Program has monitored glaciers of the Juneau Icefield.

Natural history

The bedrock consists primarily of limestone, with elevations ranging between 100 and 3000 ft. Caves are numerous.

The landscape of the plateau is mostly savanna scattered with trees. It mostly lacks deep soil suitable for farming, though the soil type is fertile mollisol, so some cotton, grain sorghum, and oats are grown. For the most part, though, the thin soil and rough terrain areas are primarily grazing regions, with cattle, sheep, and goats (Angora and meat types) predominant. Several rivers cross the region, which generally flow to the south and east through the Texas Hill Country toward the Gulf of Mexico; springs occur (in wet years), but permanent surface water supplies are sparse throughout the area, except for man-made reservoirs.

Human history

First, it was used and wandered about by Jumano and Coahuiltecan groups, then the Apacheria extended into the Southern Plains by the forerunners of the Lipan and Mescalero Apaches. After the expulsion of the Apachean groups from the plains by the Comanche, this area was dominated by the Penateka band of the Southern Comanche.

History

Settled by indigenous cultures thousands of years ago, the islands were selected by Spanish colonists as sites for founding of colonial missions. Historically the Spanish influenced the Guale and Mocama chiefdoms by establishing Christian missions in their major settlements, from St. Catherine's Island south, past the Sea Islands, to Fort George Island (at present-day Jacksonville, Florida).

Both chiefdoms extended to the coastal areas on the mainland. The Mocama Province included territory to the St. Johns River in present-day Florida. The mission system ended under pressure of repeated raids by English South Carolina colonists and Indian allies. Spain ceded its territory of Florida to Great Britain in 1763.

Geography

The Grand Canyon is a river valley in the Colorado Plateau that exposes uplifted Proterozoic and Paleozoic strata, and it is also one of the six distinct physiographic sections of the Colorado Plateau province. Even though it is not the deepest canyon on land in the world (Kali Gandaki Gorge in Nepal is much deeper), the Grand Canyon is known for its visually overwhelming size and its intricate and colorful landscape. Geologically, it is significant because of the thick sequence of ancient rocks that are well preserved and exposed in the walls of the canyon. These rock layers record much of the early geologic history of the North American continent.

Uplift associated with mountain formation later moved these sediments thousands of feet upward and created the Colorado Plateau.

Geology

The Grand Canyon is part of the Colorado River basin, which has developed over the past 70 million years. For more than 150 years, scientists have gathered data, proposed new ideas, and debated sometimes contentious theories about the geologic origins of the Grand Canyon and the Colorado River. Formation of the Grand Canyon and the Colorado River may involve a complex history in which multiple factors and geologic processes have interacted over time and in different locations.

In the most recent round of "old river" vs. "young river" controversy, researchers have challenged estimates that had placed the age of the canyon at 5–6 million years. The research has aroused considerable controversy because it suggests a substantial departure from prior widely supported scientific consensus.

Climate change

Due to the increase of greenhouse gases, temperatures have steadily risen making recent years the warmest in the century-long record. Temperatures have increased in Arizona by 2.1 degrees Fahrenheit since 1895. From 1916 to 2014, naturalized streamflow in the Upper Colorado River Basin decreased by 16.5%, in spite of a slight increase of +1.4% in annual precipitation over the same period.

Increases in temperature correlate to increased evaporation, loss of reflective snow, and decreases in snowpack, reducing available water in the Colorado River by an estimated 9.3% per degree Celsius of warming.

Over the last 30 years, the South Rim of the Grand Canyon has averaged 13.4 inches of rainfall per year, while the North Rim has averaged 24 inches.

Biology and ecology

There are approximately 1,737 known species of vascular plants, 167 species of fungi, 64 species of moss, and 195 species of lichen found in Grand Canyon National Park. This variety is largely due to the 8,000 foot (2,400 m) elevation change from the Colorado River up to the highest point on the North Rim. Grand Canyon boasts a dozen endemic plants (known only within the Park's boundaries) while only ten percent of the Park's flora is exotic.

Climate

While other Alaskan ranges to the south and closer to the coast can receive 250 inches (640 cm) to 500 inches (1,300 cm) of snow, the average snow precipitation on the Brooks Range is reported at 30 inches (76 cm) to 51 inches (130 cm). Due to a changing climate, between the years 1969–2018 the Eastern and Western portions of the Brooks Range have experienced a 17.2% increase in annual precipitation.

As measured at the Anaktuvuk Pass weather station (elevation 770 metres (2,530 ft)), the average summer temperatures are 16 °C (61 °F) as a high and 3 °C (37 °F) as a low. During the winter the average high is −22 °C (−8 °F) while the average low is −30 °C (−22 °F). Polar amplification is a force experienced in this region as global temperatures are rising.

Ecology

The Brooks Range forms the northernmost drainage divide in North America, separating streams flowing into the Arctic Ocean and the North Pacific. The range roughly delineates the summer position of the Arctic front. It represents the northern extent of the tree line, with little beyond isolated balsam poplar stands occurring north of the continental drainage divide. Trembling aspen and white spruce also occur north of the Brooks Range, though they are limited to sites that have been disturbed by human activity. Southern slopes have some cover of black spruce, Picea mariana, marking the northern limit of those trees. As the global mean temperature increases, tree line has been observed to move further north, changing the boundaries of where these trees are found.

History

Bob Marshall explored the North Fork Koyukuk River area of the range in 1929. He named Mount Doonerak, explaining "the name Doonerak I took from an Eskimo word which means a spirit or, as they would translate it, a devil." Marshall described the mountain as, a "towering, black, unscalable-looking giant, the highest peak in this section of the Brooks Range."

Geography

The Malaspina Glacier actually comprises Seward Glacier, Agassiz Glacier, and Marvine/Hayden Glacier, which converge as they spill out from the Saint Elias Mountains onto the coastal plain facing the Gulf of Alaska between Icy Bay and Yakutat Bay. Officially, these three glaciers are classified independently, such that Malaspina Glacier does not technically exist. The three glaciers are almost always referred to together, though sometimes only the largest primary piedmont lobe is referred to as Malaspina Glacier. This notable feature is actually part of Seward Glacier, with Agassiz Glacier contributing the secondary piedmont lobe to the west, and Marvine/Hayden Glacier constituting the smallest and most eastern lobe.

History

Radar data and aerial photographs dating back to 1972 provide evidence that the Malaspina-Seward glacier system lost about 20 m (66 ft) of its thickness between 1980 and 2000; because the glacier is so large, that amount of shrinkage was sufficient to contribute 0.5% of the rise in the global sea level.

Geography

The Harding Icefield is over 700 square miles (1,800 km2) in its entirety (although, if one were to count its glaciers which descend from the icefield in all directions, the icefield measures in at over 1,100 square miles (2,800 km2)) The icefield spawns up to 40 glaciers of all types. Some of the more notable glaciers include the Tustumena Glacier, Exit Glacier, and McCarty Glacier. The Exit Glacier, however, is the most accessible of the glaciers, being reached by a spur road off of the Seward Highway.

The icefield is also one of four remaining icefields in the United States and is the largest contained entirely within the United States. The icefield itself receives over 400 inches (10 m) of snow each year.

History

Residents of Seward, Alaska, generally ignored the huge icefield west of town before 1922. The construction of the Spruce Creek trail that year, however, made it possible to view the upper portions of the icecap, and President Harding's promise to visit the territory was sufficient to bestow his name on the feature. Between the mid-1920s and the early 1930s, the increasing popularity of aviation had given a lucky few the opportunity to soar over the icefield. Up to this point, however, settlers had walked only on the icefield's margins.

In early 1936, a 27-year-old Swiss immigrant and future state senator named Yule Kilcher disembarked in Seward.

Geography and geology

The Wasatch Range's origins are rooted in the Sevier Orogeny. As the Farallon plate subducted under the North American plate between the Jurassic and Paleogene, the regional stress regime became a maximum striking east to west. This horizontal compression caused thin skinned imbricated thrust faults resulting in as much as 50% crustal shortening of the western North American Plate. The Wasatch anticlinorium represented the furthest eastern margins of these Sevier origin imbricated thrusts. Once the Farallon plate had largely subducted, the NW moving Pacific plate latched onto the North American Plate, causing a change in regional stress.

Ecology

The Wasatch Range is part of the Wasatch and Uinta Mountains Level 3 Ecoregion, a temperate coniferous forest. Common trees include Douglas fir (Pseudotsuga menziesii), subalpine fir (Abies bifolia), Engelmann spruce (Picea engelmannii), Colorado blue spruce (Picea pungens), and quaking aspen (Populus tremuloides). Gambel oak (Quercus gambelii) is common on the foothills of the range from just south of Brigham City in the north, to the southern extension of the Wasatch Range. It is not found in the northern portion of the Range. Ponderosa pine (Pinus ponderosa), while abundant elsewhere in Utah is not common in this mountain range, except in plantations in Big Cottonwood Canyon southeast of Salt Lake City and in Logan Canyon, east of Logan.

Overview

Since the earliest days of European settlement, most of Utah's population has chosen to settle along the range's western front, where numerous rivers exit the mountains. For early settlers, the mountains were a vital source of water, timber, and granite. Today, 85% of Utah's population lives within 15 miles (24 km) of the Wasatch Range, mainly in the valleys just to the west. This westside concentration is known as the Wasatch Front and has a population just shy of 3 million. Salt Lake City lies between the Wasatch Range and the Great Salt Lake.

The range's highest point — 11,928 feet (3,636 m) — is Mount Nebo, a triple peak rising above Nephi, at the southern end of the range.

Geography

The Black Rock Desert region is in northwestern Nevada and the northwestern Great Basin. The playa extends for approximately 100 mi (160 km) northeast from the towns of Gerlach and Empire, between the Jackson Mountains to the east and the Calico Hills to the west.

The Black Rock Desert is separated into two arms by the Black Rock Range. It lies at an elevation of 3,907 ft (1,191 m) and has an area of about 1,000 sq mi (2,600 km2).

There are several possible definitions of the extent of the Black Rock Desert. Often, people refer only to the playa surface. Sometimes, terrain which can be seen from the playa is included. The widest definition of the Black Rock Desert region is the watershed of the basin that drains into the playa.

History

More than ~15,000 years ago (15 tya), the Humboldt River flowed to the Smoke Creek–Black Rock Desert sub-basin, and during the recession of Lake Lahontan, the river diverted to the Carson Desert sub-basin. During the highest Lahontan water level (~12.7 kya), the lakebed was under about 500 ft (150 m) of water, under which sediment accumulated to form a flat lakebed.

Great Basin tribes inhabited the area approximately 10,000 B.P., and a Frémont Expedition encountered the site in 1843, but the Fortieth Parallel Survey (1867) conducted the first official exploration. In the late 1840s, Peter Lassen led California Trail emigrants through the desert's Applegate-Lassen Cutoff, an arduous route that took them hundreds of miles away from the gold lands of California.

Geology

The St. Francois Mountains in the northeastern Ozarks are the eroded remnants of an ancient range which form the geological core of the highland dome. The igneous and volcanic rocks of the St. Francois Mountains are the exposed remains of a Proterozoic mountain range hundreds of millions of years old. The remaining hills are the exposed portion of an extensive terrane (the Spavinaw terrane in part) of granitic and rhyolitic rocks dating from 1.485 to 1.350 bya that stretches from Ohio to western Oklahoma. The core of the range existed as an island in the Paleozoic seas. Reef complexes occur in the sedimentary layers surrounding this ancient island.

Ecology and conservation

Formal conservation in the region began when the Ozark National Forest was created by proclamation of President Theodore Roosevelt in 1908 to preserve 917,944 acres (3,714.79 km2) across five Arkansas counties. Another 608,537 acres (2,462.66 km2) were added the following year. The initial forest included area as far south as Mount Magazine and as far east as Sylamore.

In 1939, Congress established Mark Twain National Forest at nine sites in Missouri. Wildlife management areas were founded in the 1920s and 1930s to restore populations to viable numbers. In the 1930s and 1940s Aldo Leopold, Arthur Carhart and Bob Marshall developed a "wilderness" policy for the Forest Service.

Regional economy

The Ozarks contain ore deposits of lead, zinc, iron and barite. Many of these deposits have been depleted by historic mining activities, but much remains and is currently being mined in the Lead Belt of southeastern Missouri. Historically, the lead belt around the Saint Francois Mountains and the Tri-State district lead-zinc mining area around Joplin, Missouri, have been important sources of metals. Mining practices common in the early 20th century left significant abandoned underground mine problems and heavy metal contamination in topsoil and groundwater in the Tri-State district.

Much of the area supports beef cattle ranching, and dairy farming is common across the area.