California is a state in the Pacific Region of the United States. With 39.6 million residents, California is the most populous U. S. the third-largest by area. The state capital is Sacramento; the Greater Los Angeles Area and the San Francisco Bay Area are the nation's second and fifth most populous urban regions, with 18.7 million and 9.7 million residents respectively. Los Angeles is California's most populous city, the country's second most populous, after New York City. California has the nation's most populous county, Los Angeles County, its largest county by area, San Bernardino County; the City and County of San Francisco is both the country's second-most densely populated major city after New York City and the fifth-most densely populated county, behind only four of the five New York City boroughs. California's $3.0 trillion economy is larger than that of any other state, larger than those of Texas and Florida combined, the largest sub-national economy in the world. If it were a country, California would be the 5th largest economy in the world, the 36th most populous as of 2017.
The Greater Los Angeles Area and the San Francisco Bay Area are the nation's second- and third-largest urban economies, after the New York metropolitan area. The San Francisco Bay Area PSA had the nation's highest GDP per capita in 2017 among large PSAs, is home to three of the world's ten largest companies by market capitalization and four of the world's ten richest people. California is considered a global trendsetter in popular culture, innovation and politics, it is considered the origin of the American film industry, the hippie counterculture, fast food, the Internet, the personal computer, among others. The San Francisco Bay Area and the Greater Los Angeles Area are seen as global centers of the technology and entertainment industries, respectively. California has a diverse economy: 58% of the state's economy is centered on finance, real estate services and professional, scientific and technical business services. Although it accounts for only 1.5% of the state's economy, California's agriculture industry has the highest output of any U.
S. state. California is bordered by Oregon to the north and Arizona to the east, the Mexican state of Baja California to the south; the state's diverse geography ranges from the Pacific Coast in the west to the Sierra Nevada mountain range in the east, from the redwood–Douglas fir forests in the northwest to the Mojave Desert in the southeast. The Central Valley, a major agricultural area, dominates the state's center. Although California is well-known for its warm Mediterranean climate, the large size of the state results in climates that vary from moist temperate rainforest in the north to arid desert in the interior, as well as snowy alpine in the mountains. Over time and wildfires have become more pervasive features. What is now California was first settled by various Native Californian tribes before being explored by a number of European expeditions during the 16th and 17th centuries; the Spanish Empire claimed it as part of Alta California in their New Spain colony. The area became a part of Mexico in 1821 following its successful war for independence but was ceded to the United States in 1848 after the Mexican–American War.
The western portion of Alta California was organized and admitted as the 31st state on September 9, 1850. The California Gold Rush starting in 1848 led to dramatic social and demographic changes, with large-scale emigration from the east and abroad with an accompanying economic boom; the word California referred to the Baja California Peninsula of Mexico. The name derived from the mythical island California in the fictional story of Queen Calafia, as recorded in a 1510 work The Adventures of Esplandián by Garci Rodríguez de Montalvo; this work was the fifth in a popular Spanish chivalric romance series that began with Amadis de Gaula. Queen Calafia's kingdom was said to be a remote land rich in gold and pearls, inhabited by beautiful black women who wore gold armor and lived like Amazons, as well as griffins and other strange beasts. In the fictional paradise, the ruler Queen Calafia fought alongside Muslims and her name may have been chosen to echo the title of a Muslim leader, the Caliph. It's possible.
Know ye that at the right hand of the Indies there is an island called California close to that part of the Terrestrial Paradise, inhabited by black women without a single man among them, they lived in the manner of Amazons. They were robust of body with great virtue; the island itself is one of the wildest in the world on account of the craggy rocks. Shortened forms of the state's name include CA, Cal. Calif. and US-CA. Settled by successive waves of arrivals during the last 10,000 years, California was one of the most culturally and linguistically diverse areas in pre-Columbian North America. Various estimates of the native population range from 100,000 to 300,000; the Indigenous peoples of California included more than 70 distinct groups of Native Americans, ranging from large, settled populations living on the coast to groups in the interior. California groups were diverse in their political organization with bands, villages, on the resource-rich coasts, large chiefdoms, such as the Chumash and Salinan.
Trade, intermarriage a
In modern mapping, a topographic map is a type of map characterized by large-scale detail and quantitative representation of relief using contour lines, but using a variety of methods. Traditional definitions require a topographic map to show both man-made features. A topographic survey is published as a map series, made up of two or more map sheets that combine to form the whole map. A contour line is a line connecting places of equal elevation. Natural Resources Canada provides this description of topographic maps:These maps depict in detail ground relief, forest cover, administrative areas, populated areas, transportation routes and facilities, other man-made features. Other authors define topographic maps by contrasting them with another type of map. However, in the vernacular and day to day world, the representation of relief is popularly held to define the genre, such that small-scale maps showing relief are called "topographic"; the study or discipline of topography is a much broader field of study, which takes into account all natural and man-made features of terrain.
Topographic maps are based on topographical surveys. Performed at large scales, these surveys are called topographical in the old sense of topography, showing a variety of elevations and landforms; this is in contrast to older cadastral surveys, which show property and governmental boundaries. The first multi-sheet topographic map series of an entire country, the Carte géométrique de la France, was completed in 1789; the Great Trigonometric Survey of India, started by the East India Company in 1802 taken over by the British Raj after 1857 was notable as a successful effort on a larger scale and for determining heights of Himalayan peaks from viewpoints over one hundred miles distant. Topographic surveys were prepared by the military to assist in planning for battle and for defensive emplacements; as such, elevation information was of vital importance. As they evolved, topographic map series became a national resource in modern nations in planning infrastructure and resource exploitation. In the United States, the national map-making function, shared by both the Army Corps of Engineers and the Department of the Interior migrated to the newly created United States Geological Survey in 1879, where it has remained since.1913 saw the beginning of the International Map of the World initiative, which set out to map all of Earth's significant land areas at a scale of 1:1 million, on about one thousand sheets, each covering four degrees latitude by six or more degrees longitude.
Excluding borders, each sheet was up to 66 cm wide. Although the project foundered, it left an indexing system that remains in use. By the 1980s, centralized printing of standardized topographic maps began to be superseded by databases of coordinates that could be used on computers by moderately skilled end users to view or print maps with arbitrary contents and scale. For example, the Federal government of the United States' TIGER initiative compiled interlinked databases of federal and local political borders and census enumeration areas, of roadways and water features with support for locating street addresses within street segments. TIGER was used in the 1990 and subsequent decennial censuses. Digital elevation models were compiled from topographic maps and stereographic interpretation of aerial photographs and from satellite photography and radar data. Since all these were government projects funded with taxes and not classified for national security reasons, the datasets were in the public domain and usable without fees or licensing.
TIGER and DEM datasets facilitated Geographic information systems and made the Global Positioning System much more useful by providing context around locations given by the technology as coordinates. Initial applications were professionalized forms such as innovative surveying instruments and agency-level GIS systems tended by experts. By the mid-1990s user-friendly resources such as online mapping in two and three dimensions, integration of GPS with mobile phones and automotive navigation systems appeared; as of 2011, the future of standardized, centrally printed topographical maps is left somewhat in doubt. Topographic maps have multiple uses in the present day: any type of geographic planning or large-scale architecture; the various features shown on the map are represented by conventional symbols. For example, colors can be used to indicate a classification of roads; these signs are explained in the margin of the map, or on a separately published characteristic sheet. Topographic maps are commonly called contour maps or topo maps.
In the United States, where the primary national series is organized by a strict 7.5-minute grid, they are called topo quads or quadrangles. Topographic maps conventionally show land contours, by means of contour lines. Contour lines are curves. In other words, every point on the marked line of 100 m elevation is 100 m above mean sea level; these maps show
Sierra Nevada (U.S.)
The Sierra Nevada is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies in Nevada; the Sierra Nevada is part of the American Cordillera, a chain of mountain ranges that consists of an continuous sequence of such ranges that form the western "backbone" of North America, Central America, South America and Antarctica. The Sierra runs 400 miles north-to-south, is 70 miles across east-to-west. Notable Sierra features include the largest alpine lake in North America; the Sierra is home to three national parks, twenty wilderness areas, two national monuments. These areas include Yosemite and Kings Canyon National Parks; the character of the range is shaped by its ecology. More than one hundred million years ago during the Nevadan orogeny, granite formed deep underground; the range started to uplift four million years ago, erosion by glaciers exposed the granite and formed the light-colored mountains and cliffs that make up the range.
The uplift caused a wide range of elevations and climates in the Sierra Nevada, which are reflected by the presence of five life zones. Uplift continues due to faulting caused by tectonic forces, creating spectacular fault block escarpments along the eastern edge of the southern Sierra; the Sierra Nevada has a significant history. The California Gold Rush occurred in the western foothills from 1848 through 1855. Due to inaccessibility, the range was not explored until 1912; the Sierra Nevada lies in Central and Eastern California, with a small but important spur extending into Nevada. West-to-east, the Sierra Nevada's elevation increases from 1,000 feet in the Central Valley to heights of about 14,000 feet at its crest 50–75 miles 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.
It represents where the granitic bedrock of the Sierra Nevada dives below the southern extent of Cenozoic igneous surface rock from the Cascade Range. It is bounded on the west by California's Central Valley and on the east by the Basin and Range Province; the southern boundary is at Tehachapi Pass. Physiographically, the Sierra is a section of the Cascade-Sierra Mountains province, which in turn is part of the larger Pacific Mountain System physiographic division; the California Geological Survey states that "the northern Sierra boundary is marked where bedrock disappears under the Cenozoic volcanic cover of the Cascade Range." The range is drained on its western slope by the Central Valley watershed, which discharges into the Pacific Ocean at San Francisco. The northern third of the western Sierra is part of the Sacramento River watershed, the middle third is drained by the San Joaquin River; the southern third of the range is drained by the Kings, Kaweah and Kern rivers, which flow into the endorheic basin of Tulare Lake, which overflows into the San Joaquin during wet years.
The eastern slope watershed of the Sierra is much narrower. From north to south, the Susan River flows into intermittent Honey Lake, the Truckee River flows from Lake Tahoe into Pyramid Lake, the Carson River runs into Carson Sink, the Walker River into Walker Lake. Although none of the eastern rivers reach the sea, many of the streams from Mono Lake southwards are diverted into the Los Angeles Aqueduct which provides water to Southern California; the height of the mountains in the Sierra Nevada increases from north to south. Between Fredonyer Pass and Lake Tahoe, the peaks range from 5,000 feet to more than 9,000 feet; the crest near Lake Tahoe is 9,000 feet high, with several peaks approaching the height of Freel Peak. Farther south, the highest peak in Yosemite National Park is Mount Lyell; the Sierra rises to 14,000 feet with Mount Humphreys near Bishop, California. Near Lone Pine, Mount Whitney is at 14,505 feet, the highest point in the contiguous United States. South of Mount Whitney, the elevation of the range dwindles.
The crest elevation is 10,000 feet near Lake Isabella, but south of the lake, the peaks reach to only a modest 8,000 feet. There are several notable geographical features in the Sierra Nevada: Lake Tahoe is a large, clear freshwater lake in the northern Sierra Nevada, with an elevation of 6,225 ft and an area of 191 sq mi. Lake Tahoe lies between a spur of the Sierra. Hetch Hetchy Valley, Yosemite Valley, Kings Canyon, Kern Canyon are examples of many glacially-scoured canyons on the west side of the Sierra. Yosemite National Park is filled with notable features such as waterfalls, granite domes, high mountains and meadows. Groves of Giant Sequoia
Kings Canyon National Park
Kings Canyon National Park is an American national park in the southern Sierra Nevada, in Fresno and Tulare Counties, California. Established in 1890 as General Grant National Park, the park was expanded and renamed to Kings Canyon National Park on March 4, 1940; the park's namesake, Kings Canyon, is a rugged glacier-carved valley more than a mile deep. Other natural features include multiple 14,000-foot peaks, high mountain meadows, swift-flowing rivers, some of the world's largest stands of giant sequoia trees. Kings Canyon is north of and contiguous with Sequoia National Park, the two are jointly administered by the National Park Service as the Sequoia and Kings Canyon National Parks; the majority of the 461,901-acre park, drained by the Middle and South Forks of the Kings River and many smaller streams, is designated wilderness. Tourist facilities are concentrated in two areas: Grant Grove, home to General Grant and Cedar Grove, located in the heart of Kings Canyon. Overnight hiking is required to access most of the park's backcountry, or high country, which for much of the year is covered in deep snow.
The combined Pacific Crest Trail/John Muir Trail, a backpacking route, traverses the entire length of the park from north to south. General Grant National Park was created to protect a small area of giant sequoias from logging. Although John Muir's visits brought public attention to the huge wilderness area to the east, it took more than fifty years for the rest of Kings Canyon to be designated a national park. Environmental groups, park visitors and many local politicians wanted to see the area preserved. After President Franklin D. Roosevelt expanded the park in 1940, the fight continued until 1965, when the Cedar Grove and Tehipite Valley dam sites were annexed into the park; as visitation rose post–World War II, further debate took place over whether the park should be developed as a tourist resort, or retained as a more natural environment restricted to simpler recreation such as hiking and camping. The preservation lobby prevailed and today, the park has only limited services and lodgings despite its size.
Due to this and the lack of road access to most of the park, Kings Canyon remains the least visited of the major Sierra parks, with just under 700,000 visitors in 2017 compared to 1.3 million visitors at Sequoia and over 4 million at Yosemite. Kings Canyon National Park, located on the western slope of the Sierra Nevada to the east of the San Joaquin Valley, is divided into two distinct sections; the smaller and older western section centers around Grant Grove – home of many of the park's sequoias – and has most of the visitor facilities. The larger eastern section, which accounts for the majority of the park's area, is entirely wilderness, contains the deep canyons of the Middle and South Forks of the Kings River. Cedar Grove, located at the bottom of the Kings Canyon, is the only part of the park's vast eastern portion accessible by road. Although most of the park is forested, much of the eastern section consists of alpine regions above the tree line. Snow free only from late June until late October, the high country is accessible via foot and horse trails.
The Sequoia-Kings Canyon Wilderness encompasses over 768,000 acres in Kings Canyon and Sequoia National Parks, or nearly 90 percent of their combined area. In addition to Sequoia National Park on the south, Kings Canyon is surrounded by multiple national forests and wilderness areas; the Sierra National Forest, Sequoia National Forest and Inyo National Forest border it on the northwest and east, respectively. The John Muir Wilderness wraps around much of the northern half of the park, the Monarch Wilderness preserves much of the area between the park's two sections. Kings Canyon is characterized by some of the steepest vertical relief in North America, with numerous peaks over 14,000 feet on the Sierra Crest along the park's eastern border, falling to 4,500 feet in the valley floor of Cedar Grove just ten miles to the west; the Sierran crest forms the eastern boundary of the park, from Mount Goethe in the north, down to Junction Peak, at the boundary with Sequoia National Park. Several passes cross the crest into the park, including Bishop Pass, Taboose Pass, Sawmill Pass, Kearsarge Pass.
All of these passes are above 11,000 feet in elevation. There are several prominent subranges of the Sierra around the park; the Palisades, along the park's eastern boundary, have four peaks over 14,000 feet including the highest point in the park, 14,248 feet NAVD 88 at the summit of North Palisade. The Great Western Divide extends through the south-central part of the park and has many peaks over 13,000 feet, including Mount Brewer; the Monarch Divide, stretching between the lower Middle and South Forks of the Kings, has some of the most inaccessible terrain in the entire park. In the northwest section of the park are other steep and rugged ranges such as the Goddard Divide, LeConte Divide and Black Divide, all of which are dotted with high mountain lakes and separated by deep chasms. Most of the mountains and canyons, as in other parts of the Sierra Nevada, are formed in igneous intrusive rocks such as granite and monzonite, formed at least 100 million years ago due to subduction along the North American–Pacific Plate boundary.
However, the Sierra itself is a young mountain range, no more than 10 million years old. Huge tectonic forces along the western edge of the Great Basin forced the local crustal block to tilt and uplift, crea
Fresno County, California
Fresno County the County of Fresno, is a county located in the central portion of the U. S. state of California. As of January 1, 2018, the population was 1,007,229; the county seat is the fifth-largest city in California. Fresno County comprises the Fresno, CA Metropolitan Statistical Area, part of the Fresno-Madera, CA Combined Statistical Area, it is located in north of Bakersfield. The area now known as Fresno County was the traditional homeland of Yokuts and Mono peoples, was settled by Spaniards during a search for suitable mission sites. In 1846, this area became part of the United States as a result of the Mexican War. Fresno County was formed in 1856 from parts of Mariposa and Tulare counties. Fresno is Spanish for "ash tree" and it was in recognition of the abundance of the shrubby local Ash, Fraxinus dipetala, growing along the San Joaquin River that it received its name. Parts of Fresno County's territory were given to Mono County in 1861 and to Madera County in 1893; the original county seat was along the San Joaquin River in Millerton, but was moved to the growing town of Fresno on the newly built Southern Pacific Railroad line after a flood destroyed much of the town.
The settling of Fresno County was not without its conflicts, land disputes, other natural disasters. Floods caused immeasurable damage elsewhere and fires plagued the settlers of Fresno County. In 1882, the greatest of the early day fires wiped out an entire block of the city of Fresno, was followed by another devastating blaze in 1883. At the same time residents brought irrigation and extensive agriculture to the area. Moses Church developed the first canals, called "Church Ditches," for irrigation; these canals allowed extensive cultivation of wheat. Francis Eisen, leader of the wine industry in Fresno County began the raisin industry in 1875, when he accidentally let some of his grapes dry on the vine. A. Y. Easterby and Clovis Cole developed extensive grain and cattle ranches; these and other citizens laid the groundwork for the cultivation of Fresno County – now one of the nation's leading agricultural regions. In more recent times cotton became a major crop in Fresno and the southern San Joaquin Valley, but recent drought and lower demand have lessened cotton's importance to the local economy.
The discovery of oil in the western part of the county, near the town of Coalinga at the foot of the Coast Ranges, brought about an economic boom in the 1900s though the field itself was known at least as early as the 1860s. By 1910, Coalinga Oil Field, the largest field in Fresno County, was the most richly productive oil field in California; the Coalinga field continues to produce oil, is the eighth-largest field in the state. More than thirty structures in Fresno County are on the National Register of Historic Places, including the Fresno Water Tower, which once held over 250,000 US gallons of water for the city of Fresno, the Meux Home, Kearney Mansion Museum. According to the U. S. Census Bureau, the county has a total area of 6,011 square miles, of which 5,958 square miles is land and 53 square miles is water. Major watercourses are the San Joaquin River, Kings River, Delta-Mendota Canal, Big Creek, Friant Kern Canal, Helm Canal and Madera Canal, it is bordered on the west on the east by the Sierra Nevada.
It is the center of a large agricultural area, known as the most agriculturally rich county in the United States. The county withdrew 3.7 billion US gallons of fresh water per day in 2000, more than any other county in the United States. Fresno County is part of the Madera AVA wine region. Fresno was named after two particular ash trees that grew near the town of Minkler on the Kings River, one of, still alive and standing. Giant Sequoia National Monument Kings Canyon National Park Sequoia National Forest Sierra National Forest A number of minerals have been discovered in the county, including macdonaldite, walstromite, verplanckite, muirite and kampfite; the 2010 United States Census reported that Fresno County had a population of 930,450. The racial makeup of Fresno County was 515,145 White, 49,523 African American, 15,649 Native American, 89,357 Asian, 1,405 Pacific Islander, 217,085 from other races, 42,286 from two or more races. Hispanic or Latino of any race were 468,070 persons. 46.0% of Fresno County's population is of Mexican descent.
As of the census of 2000, there were 799,407 people, 252,940 households, 186,669 families residing in the county. The population density was 134 people per square mile. There were 270,767 housing units at an average density of 45 per square mile; the racial makeup of the county was 54.3% White, 5.3% Black or African American, 1.6% Native American, 8.1% Asian, 0.1% Pacific Islander, 25.9% from other races, 4.7% from two or more races. 44.0% of the population were Hispanic or Latino of any race. 7.5% were of German ancestry according to Census 2000. 59.3% spoke English, 31.5% Spanish and 3.1% Hmong as their first language. There were 252,940 households ou
A summit is a point on a surface, higher in elevation than all points adjacent to it. The topographic terms acme, apex and zenith are synonymous; the term top is used only for a mountain peak, located at some distance from the nearest point of higher elevation. For example, a big massive rock next to the main summit of a mountain is not considered a summit. Summits near a higher peak, with some prominence or isolation, but not reaching a certain cutoff value for the quantities, are considered subsummits of the higher peak, are considered part of the same mountain. A pyramidal peak is an exaggerated form produced by ice erosion of a mountain top. Summit may refer to the highest point along a line, trail, or route; the highest summit in the world is Everest with height of 8844.43 m above sea level. The first official ascent was made by Sir Edmund Hillary, they reached the mountain`s peak in 1953. Whether a highest point is classified as a summit, a sub peak or a separate mountain is subjective; the UIAA definition of a peak is.
Otherwise, it's a subpeak. In many parts of the western United States, the term summit refers to the highest point along a road, highway, or railroad. For example, the highest point along Interstate 80 in California is referred to as Donner Summit and the highest point on Interstate 5 is Siskiyou Mountain Summit. A summit climbing differs from the common mountaineering. Summit expedition requires: 1+ year of training, a good physical shape, a special gear. Although a huge part of climber’s stuff can be left and taken at the base camps or given to porters, there is a long list of personal equipment. In addition to common mountaineers’ gear, Summit climbers need to take Diamox and bottles of oxygen. There are special requirements for crampons, ice axe, rappel device, etc. Geoid Hill – Landform that extends above the surrounding terrain Nadir Summit accordance Peak finder Summit Climbing Gear List
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, the natural hazards that threaten it; the organization has four major science disciplines, concerning biology, geography and hydrology. The USGS is a fact-finding research organization with no regulatory responsibility; the USGS is a bureau of the United States Department of the Interior. The USGS employs 8,670 people and is headquartered in Reston, Virginia; the USGS has major offices near Lakewood, Colorado, at the Denver Federal Center, Menlo Park, California. The current motto of the USGS, in use since August 1997, is "science for a changing world." The agency's previous slogan, adopted on the occasion of its hundredth anniversary, was "Earth Science in the Public Service." Since 2012, the USGS science focus is directed at six topical "Mission Areas", namely Climate and Land Use Change, Core Science Systems, Ecosystems and Minerals and Environmental Health, Natural Hazards, Water.
In December 2012, the USGS split the Energy and Minerals and Environmental Health Mission Area resulting in seven topical Mission Areas, with the two new areas being: Energy and Minerals and Environmental Health. Administratively, it is divided into six Regional Units. Other specific programs include: Earthquake Hazards Program monitors earthquake activity worldwide; the National Earthquake Information Center in Golden, Colorado on the campus of the Colorado School of Mines detects the location and magnitude of global earthquakes. The USGS runs or supports several regional monitoring networks in the United States under the umbrella of the Advanced National Seismic System; the USGS informs authorities, emergency responders, the media, the public, both domestic and worldwide, about significant earthquakes. It maintains long-term archives of earthquake data for scientific and engineering research, it conducts and supports research on long-term seismic hazards. USGS has released the UCERF California earthquake forecast.
As of 2005, the agency is working to create a National Volcano Early Warning System by improving the instrumentation monitoring the 169 volcanoes in U. S. territory and by establishing methods for measuring the relative threats posed at each site. The USGS National Geomagnetism Program monitors the magnetic field at magnetic observatories and distributes magnetometer data in real time; the USGS collaborates with Canadian and Mexican government scientists, along with the Commission for Environmental Cooperation, to produce the North American Environmental Atlas, used to depict and track environmental issues for a continental perspective. The USGS operates the streamgaging network for the United States, with over 7400 streamgages. Real-time streamflow data are available online. National Climate Change and Wildlife Science Center implements partner-driven science to improve understanding of past and present land use change, develops relevant climate and land use forecasts, identifies lands and communities that are most vulnerable to adverse impacts of change from the local to global scale.
Since 1962, the Astrogeology Research Program has been involved in global and planetary exploration and mapping. In collaboration with Stanford University, the USGS operates the USGS-Stanford Ion Microprobe Laboratory, a world-class analytical facility for U--Pb geochronology and trace element analyses of minerals and other earth materials. USGS operates a number of water related programs, notably the National Streamflow Information Program and National Water-Quality Assessment Program. USGS Water data is publicly available from their National Water Information System database; the USGS operates the National Wildlife Health Center, whose mission is "to serve the nation and its natural resources by providing sound science and technical support, to disseminate information to promote science-based decisions affecting wildlife and ecosystem health. The NWHC provides information, technical assistance, research and leadership on national and international wildlife health issues." It is the agency responsible for surveillance of H5N1 avian influenza outbreaks in the United States.
The USGS runs 17 biological research centers in the United States, including the Patuxent Wildlife Research Center. The USGS is investigating collaboration with the social networking site Twitter to allow for more rapid construction of ShakeMaps; the USGS produces several national series of topographic maps which vary in scale and extent, with some wide gaps in coverage, notably the complete absence of 1:50,000 scale topographic maps or their equivalent. The largest and best-known topographic series is the 7.5-minute, 1:24,000 scale, quadrangle, a non-metric scale unique to the United States. Each of these maps covers an area bounded by two lines of latitude and two lines of longitude spaced 7.5 minutes apart. Nearly 57,000 individual maps in this series cover the 48 contiguous states, Hawaii, U. S. territories, areas of Alaska near Anchorage and Prudhoe Bay. The area covered by each map varies with the latitude of its represented location due to convergence of the meridians. At lower latitudes, near 30° north, a 7.5-minute quadrangle contains an area of about 64 square miles.
At 49° north latitude, 49 square miles are contained within a quadrangle of that size. As a unique non-metric map scale, the 1:24,000 scale requires a separate and specialized romer scale for pl