[17], When the North American Plate on its slow journey westwards encountered the Pacific Plate approximately 250 million years ago during the Paleozoic, the latter began to subduct under the North American continent. To the north it is bordered by the watershed of the Tuolumne River, the other major river draining Yosemite National Park. Moraines are made up of pieces of rock that are shattered by frost action, embedded in the glaciers & brought down the valley. [26], In the early 19th century, several military expeditions sent by Spanish colonists from coastal California traveled into the Central Valley. The California Gold Rush brought many people into California and some settled in towns along the lower Merced River. Glaciers such as Classen, Godley and Douglas now all have new glacial lakes below their terminal locations due to the glacial retreat over the past 20 years. [15], Of the 127 bird species found along the Merced River, only 35 occur along the entire length of the river. Glaciated landscapes are formed by a combination of erosion, transportation and deposition processes. Many depositional landforms result from sediment deposited or reshaped by Those that fall on the sides of the glacier form lateral moraines. The Lake McClure gauge, located at the former mining town of Bagby, is probably the most accurate gauge for flows overall. The lowermost, the Crocker-Huffman Diversion Dam, was built in 1906 and completely blocks the passage of anadromous fish up the Merced River. Anadromous fish species found in the lower river are chinook salmon, Pacific lamprey and striped bass. Later, when the glaciers retreated leaving behind their freight of crushed rock and sand (glacial drift), they created characteristic depositional landforms.Examples include glacial moraines, eskers, and kames. Common species of bird throughout the basin include ruby-crowned kinglet, cedar waxwing, American robin, yellow-rumped warbler, tree swallow and European starling, and several endangered species, including white-tailed kite and Swainson's hawk. Lateral moraines are those formed at the side of the ice flow, and terminal moraines were formed at the foot, marking the maximum advance of the glacier. The meltwater at the snout of the glacier deposits its load of sediment over the outwash plain, with larger boulders being Before irrigation started in the Central Valley and dams were constructed, the river's natural flow at the mouth was much higher than the current average of 661 cubic feet per second (18.7m3/s), or about 479,000 acre-feet (591,000,000m3) per year. Since the 1970s, the annual chinook run has averaged about 5,300. Kettles are formed when glacial retreat and melting is rapid, and blocks of ice are still buried under till. Irrigation return flows carry pesticides, fertilizer and other pollutants into the river. Quick facts, basic science, and information about snow, ice, and why the cryosphere matters The cryosphere includes all of the snow and ice-covered regions across the planet. [36], Irrigation with water from the Merced River continued to grow substantially until most of the arable land around the river, some 120,000 acres (490km2), was under cultivation. They named the river Rio de Nuestra Seora de la Merced (River of Our Lady of Mercy), who is the patron saint of the diocese of Barcelona and is celebrated on September 24. Fall chinook salmon travel up a fish ladder into the hatchery's pools, which are supplied with water diverted from the Merced River.[15][37]. The Merced River watershed encompasses 1,726 square miles (4,470km2) in the central Sierra Nevada. [6][7] The foothills experience a drier Mediterranean climate, while the San Joaquin Valley floor is dry enough to be considered semi-desert. El Portal Road, constructed through Merced Canyon in 1926, put an end to passenger service on the railway, but operations continued until the mid-1940s, when major flooding occurred, destroying sections of the railroad. Lateral moraines are those formed at the side of the ice flow, and terminal moraines were formed at the foot, marking the maximum advance of the glacier. [3] From its headwaters, the river flows north for a short distance and collects the Lyell Peak Fork. When lateral moraines adjacent to each other join, they create medial moraines, which are also carried down on the surface of the moving ice. Over millions of years, the Merced cut a deep canyon through the softer sedimentary rock, eventually hitting the hard granite beneath. [30] Following the construction of the Central Pacific and Southern Pacific Railroads, many of the river towns on the Merced River were deserted. There are no trails along some segments, including the lower Bridalveil Creek, upper South Fork, and specifically Tenaya Canyon, which is extremely dangerous.[6]. Other types of moraine include ground moraines (till-covered areas forming sheets on flat or irregular topography) and medial moraines (moraines formed where two glaciers meet). This moraine was actually one of several moraines deposited by the four glaciations, which include Medial Moraine and Bridalveil Moraine. These glaciers rose in branches upstream of Yosemite Valley, descending from the Merced River headwaters, Tenaya Canyon and Illilouette Creek. A true fjord is formed when a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock. The first two record flows unaffected by dams and human intervention, but discharge at the mouth is chiefly controlled by New Exchequer Dam. In other words, it is concerned with those geological factors that influence the location, design, construction and maintenance of engineering works. Environmental measures enacted in the late 20th century have had some success in boosting chinook salmon populations, from a record low of 500 fish during several years in the 1950s, to a high of 30,000 in 1984. The Sierra receives heavy snowfall in the winter, which melts in the spring and early summer causing annual flooding. Despite its partial status as a National Wild and Scenic River, the Merced River has many dams and irrigation diversions. [13], According to a study in 2006, there were 37 fish species, 127 bird species, and 140 insect and invertebrate species found in the Merced River watershed. On the south, the Merced watershed borders on the headwaters of the San Joaquin River. Medial moraines are formed when two different glaciers merge and the lateral moraines of each coalesce to form a moraine in the middle of the combined glacier. Upriver of the Merced River confluence with the San Joaquin, the latter river was usually dry, only regaining flow where the Merced River enters. These various areas of the lake have their own names. A V shaped valley is formed due to the erosional work of a river. An outwash plain, also called a sandur (plural: sandurs), sandr or sandar, is a plain formed of glaciofluvial deposits due to meltwater outwash at the terminus of a glacier.As it flows, the glacier grinds the underlying rock surface and carries the debris along. There are many activities within the watershed, including boating, fishing, camping and hiking. Due to differences in climate, there is a large disparity between species found in the upper watershed (above Lake McClure) and along the lower river. The first was Coulterville Road, followed by Big Oak Flat Road, a trading route from Stockton to Merced Canyon. Around 11,000 years ago, the terminus of the glacier was in the Rhne Valley and the glacier's edge reached almost as far as Riederfurka. [27] Moraga's expedition was part of a series of exploratory ventures, funded by the Spanish government, to find suitable sites for missions in the Central Valley and the Sierra Nevada foothills. Lake Constance was formed by the Rhine Glacier during the ice age and is a Zungenbecken or tongue lake. Together, these diversions remove almost half the natural flow of the Merced River, and an even greater proportion during dry years. Drumlins and ribbed moraines are also landforms left behind by retreating glaciers. Originally built to generate hydropower, the dam was decommissioned in 1985 but remained standing for a number of years afterward. [18] Extensive layers of marine sedimentary rock that originally made up the ancient Pacific seabed were also pushed up by the rising granite, and the ancestral Merced River formed on this layer of rock. The river first formed as the Sierra Nevada rose about 10 million years ago, and sediment eroded from its canyon helped form the flat floor of the San Joaquin Valley. It is strongly characterised and divided into different areas by end moraines, various glacial snouts and medial moraines. Little Yosemite Valley formed as a result of the underlying rock being harder than that below the Giant Staircase, the cliff wall containing Vernal Fall and Nevada Fall. [24][25] Paiute, of origin from the eastern Sierra near the Mono Lake area, also lived in the upper watershed of the Merced River. The old concrete arch dam, completed in 1926, was flooded out when the new concrete-faced rockfill dam was built in 1967, but occasionally reappears during periods of low water. [19], Over about 80 million years, erosion caused the transportation of massive amounts of alluvial sediment to the floor of the Central Valley, where it was trapped between the California Coast Range on the west and the Sierra Nevada on the east, forming an incredibly flat and fertile land surface. [40] Below this dam is Merced Falls Dam, an irrigation diversion dam. The upper section of the river, defined as the stretch from Lake McClure to the headwaters, has 11 species of fish. The river then turns generally westward for another 3 miles (4.8km), where it snakes through a spectacular narrow gorge between massive, glacially resistant granite cliffs. Today, the Merced River above Lake McClure is completely free-flowing and unobstructed by any dams. As noted in the Preface to the first edition, engineering geology can be defined as the application of Geology to engineering practice. This moraine was actually one of several moraines deposited by the four glaciations, which include Medial Moraine and Bridalveil Moraine. When the ice under the till melts, the till slumps in and forms depressions called kettles. When lateral moraines adjacent to each other join, they create medial moraines, which are also carried down on the surface of the moving ice. Moraines are made up of pieces of rock that are shattered by frost action, embedded in the glaciers & brought down the valley. When two glaciers converge, their inside lateral moraines unite to form a medial moraine. To the east, it is bordered by the Sierra crest which divides it from the endorheic Great Basin watershed of Mono Lake. Following the gold rush, the Ahwahnechee were allowed back into Yosemite Valley, but further incidents prompted a second battalion to drive them out, this time to the Mono Lake area. Triple Peak Fork, Lyell Fork, Sunrise Creek, This page was last edited on 29 October 2022, at 22:52. moraines and erratics. A true fjord is formed when a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock. Moraines. [16] Common insects found along the river include mayflies, stoneflies and caddisflies. Those that fall on the sides of the glacier form lateral moraines. Squirrels, raccoon, jackrabbits, bats, skunks, beavers, mule deer, coyote, bobcat and black bear are among the mammal species found in the middle and upper watershed. This glossary of geography terms is a list of definitions of terms and concepts used in geography and related fields, including Earth science, oceanography, cartography, and human geography, as well as those describing spatial dimension, topographical features, natural resources, and the collection, analysis, and visualization of geographic data.. Related terms may be found in One of these trips, headed by lieutenant Gabriel Moraga, arrived on the south bank of the Merced River on September 29, 1806. Below New Exchequer, the river flows west through a heavily irrigated region of the Central Valley, passing through McSwain and Crocker-Huffman Dams and the cities of Hopeton, Delhi and Livingston. Several cities that did achieve prominence, however, include Merced and Turlock, both located on the railroad.[31]. Depending ond the location of the deposits, moraines can be divided into 4 types: ground moraines, lateral moraines, medial moraines and terminal moraines. In 1808 and 1810, Moraga led further expeditions along the lower Merced River below Merced Canyon, each time coming to nothing. Classified as a "high hazard" structure, it was originally considered for inclusion on the National Register of Historic Places but was deemed too dangerous, and was subsequently removed. After the great flood of 1997, the U.S. Bureau of Reclamation surveyed the dam and found it in danger of failure. Drumlins and ribbed moraines are also landforms left behind by retreating glaciers. Satellite imagery indicates that these lakes are continuing to expand. Depending ond the location of the deposits, moraines can be divided into 4 types: ground moraines, lateral moraines, medial moraines and terminal moraines. The immense lateral moraine that was formed in the process is clearly visible from the moraine trail. Glaciology is an interdisciplinary Earth science that integrates geophysics, geology, physical geography, geomorphology, climatology, meteorology, hydrology, biology, and ecology. Sediments formed in these different environments have different characteristics (particle size and sorting) because of their mode of deposition. The Sierra (or Mountain) Miwok lived in the upper Merced Canyon and in Yosemite Valley, and at the time the first white explorers came to the area, there were about 450 Sierra Miwok split among ten permanent villages. In 1991, a fish hatchery, the Merced River Hatchery, was built beside the Merced River just downstream of the Crocker-Huffman Diversion Dam, the lowermost Merced River dam. [14], There are 26 species of native and introduced fish in the lower Central Valley portion of the river, including Sacramento sucker, smallmouth bass, largemouth bass and carp. [14], Many species of plants are found throughout the middle and upper basin, including California poppy, white alder, Oregon ash, oak, poison oak, bigleaf maple, Indian rhubarb, buttonbush, willow, whiteleaf manzanita, and historically, sugar pine, before heavy logging in the late 19th century. The California Gold Rush in the 1850s saw gradually increasing mining in Merced Canyon and Yosemite Valley. 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