The desert tortoises known as desert turtles, are two species of tortoise native to the Mojave and Sonoran Deserts of the southwestern United States and northwestern Mexico and the Sinaloan thornscrub of northwestern Mexico. G. agassizii is distributed in western Arizona, southeastern California, southern Nevada, southwestern Utah. The specific name agassizii is in honor of Swiss-American zoologist Jean Louis Rodolphe Agassiz. On the basis of DNA, behavioral differences between desert tortoises east and west of the Colorado River, it was decided that two species of desert tortoises exist: Agassiz's desert tortoise and Morafka's desert tortoise. G. morafkai occurs east of the Colorado River in Arizona, as well as in the states of Sonora and Sinaloa, Mexico. This species may be a composite of two species; the new species name is in honor of the late Professor David Joseph Morafka of California State University, Dominguez Hills, in recognition of his many contributions to the study and conservation of Gopherus.
The desert tortoise lives about 50 to 80 years. It spends most of its time in burrows, rock shelters, pallets to regulate body temperature and reduce water loss, it is inactive during most of the year. This inactivity helps reduce water loss during hot periods, whereas winter hibernation facilitates survival during freezing temperatures and low food availability. Desert tortoises can tolerate water and energy imbalances on a daily basis, which increases their lifespans; these tortoises may attain a length of 10 to 14 in, with males being larger than females. A male tortoise has a longer gular horn than a female, his plastron is concave compared to a female tortoise. Males have larger tails, their shells are high-domed, greenish-tan to dark brown in color. Desert tortoises can grow to 4–6 in in height, they can range in weight from.02 to 5 kg. The front limbs are flattened for digging. Back legs are skinnier and long. Desert tortoises can live in areas with ground temperatures exceeding 140 °F because of their ability to dig underground burrows and escape the heat.
At least 95% of their lives are spent in burrows. There, they are protected from freezing winter weather while dormant, from November through February or March. Within their burrows, these tortoises create a subterranean environment that can be beneficial to other reptiles, mammals and invertebrates. Scientists have divided the desert tortoise into two types: Agassiz's and Morafka's desert tortoises, with a possible third type in northern Sinaloan and southern Sonora, Mexico. An isolated population of Agassiz's desert tortoise occurs in the Black Mountains of northwestern Arizona, they live from sandy flats to rocky foothills. They have a strong proclivity in the Mojave Desert for alluvial fans and canyons where more suitable soils for den construction might be found, they range from near sea level to around 3,500 feet in elevation. Tortoises show strong site fidelity, have well-established home ranges where they know where their food and mineral resources are. Desert tortoises inhabit elevations from below mean sea level in Death Valley to 5,300 feet in Arizona, though they are most common from around 1,000 to 3,500 feet.
Estimates of densities vary from less than eight individuals/km2 on sites in southern California to over 500 individuals/km2 in the western Mojave Desert, although most estimates are less than 150 individuals/km2. The home range consists of 10 to 100 acres. In general, males have larger home ranges than females, home range size increases with increasing resources and rainfall. Desert tortoises are sensitive to the soil type, owing to their reliance on burrows for shelter, reduction of water loss, regulation of body temperature; the soil should crumble during digging and be firm enough to resist collapse. Desert tortoises prefer sandy loam soils with varying amounts of gravel and clay, tend to avoid sands or soils with low water-holding capacity, excess salts, or low resistance to flooding, they may consume soil to maintain adequate calcium levels, so may prefer sites with higher calcium content. Desert tortoises spend most of their lives in burrows, rock shelters, pallets to regulate body temperature and reduce water loss.
Burrows are tunnels dug into soil by desert tortoises or other animals, rock shelters are spaces protected by rocks and/or boulders, pallets are depressions in the soil. The use of the various shelter types is related to their climate; the number of burrows used, the extent of repetitive use, the occurrence of burrow sharing are variable. Males tend to occupy deeper burrows than females. Seasonal trends in burrow use are influenced by regional variation. Desert tortoise shelter sites are associated with plant or rock cover. Desert tortoises lay their eggs in nests dug in sufficiently deep soil at the entrance of burrows or under shrubs. Nests are 3 to 10 inches deep. Shelters are important for controlling body temperature and water regulation, as they allow desert tortoises to slow their rate of heating in summer and provide protection from cold during the winter; the humidity within burrows prevents dehydration. Burrows provide protection from predators; the availability of adequate burrow sites influences desert tortoise densities.
The number of burrows used by
Mojave National Preserve
Mojave National Preserve is a United States National Preserve located in the Mojave Desert of San Bernardino County, California, USA, between Interstate 15 and Interstate 40. The preserve was established October 31, 1994, with the passage of the California Desert Protection Act by the US Congress, it was the East Mojave National Scenic Area, under the jurisdiction of the Bureau of Land Management. Mojave National Preserve is vast. At 1,600,000 acres, it is the third largest unit of the National Park System in the contiguous United States. Natural features include the Kelso Dunes, the Marl Mountains and the Cima Dome, as well as volcanic formations such as Hole-in-the-Wall and the Cinder Cone Lava Beds; the preserve encloses Providence Mountains State Recreation Area and Mitchell Caverns Natural Preserve, which are both managed by the California Department of Parks and Recreation. Impressive Joshua tree forests are found in parts of the preserve; the forest covering Cima Dome and the adjacent Shadow Valley is the largest and densest in the world.
The ghost town of Kelso is found in the preserve, with the defunct railroad depot serving as the Visitor Center. The preserve is traversed by 4 wheel drive vehicles traveling on the historic Mojave Road. Climate in the preserve varies greatly. Summer temperatures average 90 °F, with highs exceeding 105 °F. Elevations in the preserve range from 7,929 feet at Clark Mountain to 880 feet near Baker. Annual precipitation varies from 3.37 inches near Baker, to 9 inches in the mountains. At least 25% of precipitation comes from summer thunderstorms. Snow is found in the mountains during the winter; the California Desert Protection Act of 1994 designated a wilderness area within Mojave National Preserve of 695,200 acres. The National Park Service manages the wilderness in accordance with the Wilderness Act, the CDPA, other laws that protect cultural and historic sites in the wilderness; the following climate data is for a higher elevation area in the preserve. See Climate of the Mojave Desert. Mojave Memorial Cross Official website Photo tour of Mojave National Preserve - from USGS
Endemism is the ecological state of a species being unique to a defined geographic location, such as an island, country or other defined zone, or habitat type. The extreme opposite of endemism is cosmopolitan distribution. An alternative term for a species, endemic is precinctive, which applies to species that are restricted to a defined geographical area; the word endemic is from New Latin endēmicus, from Greek ενδήμος, endēmos, "native". Endēmos is formed of en meaning "in", dēmos meaning "the people"; the term "precinctive" has been suggested by some scientists, was first used in botany by MacCaughey in 1917. It is the equivalent of "endemism". Precinction was first used by Frank and McCoy. Precinctive seems to have been coined by David Sharp when describing the Hawaiian fauna in 1900: "I use the word precinctive in the sense of'confined to the area under discussion'...'precinctive forms' means those forms that are confined to the area specified." That definition excludes artificial confinement of examples by humans in far-off botanical gardens or zoological parks.
Physical and biological factors can contribute to endemism. The orange-breasted sunbird is found in the fynbos vegetation zone of southwestern South Africa; the glacier bear is found only in limited places in Southeast Alaska. Political factors can play a part if a species is protected, or hunted, in one jurisdiction but not another. There are two subcategories of endemism: neoendemism. Paleoendemism refers to species that were widespread but are now restricted to a smaller area. Neoendemism refers to species that have arisen, such as through divergence and reproductive isolation or through hybridization and polyploidy in plants. Endemic types or species are likely to develop on geographically and biologically isolated areas such as islands and remote island groups, such as Hawaii, the Galápagos Islands, Socotra. Hydrangea hirta is an example of an endemic species found in Japan. Endemics can become endangered or extinct if their restricted habitat changes, particularly—but not only—due to human actions, including the introduction of new organisms.
There were millions of both Bermuda petrels and "Bermuda cedars" in Bermuda when it was settled at the start of the seventeenth century. By the end of the century, the petrels were thought extinct. Cedars ravaged by centuries of shipbuilding, were driven nearly to extinction in the twentieth century by the introduction of a parasite. Bermuda petrels and cedars are now rare. Principal causes of habitat degradation and loss in endemistic ecosystems include agriculture, urban growth, surface mining, mineral extraction, logging operations and slash-and-burn agriculture
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
A bajada consists of a series of coalescing alluvial fans along a mountain front. These fan-shaped deposits form by the deposition of sediment within a stream onto flat land at the base of a mountain; the usage of the term in landscape description or geomorphology derives from the Spanish word bajada having the sense of "descent" or "inclination". When a stream flows downhill it picks up sediment along with other materials, as that stream emerges from a mountain front the sediment begins to deposit; the coarser sediment falls out closest to the base and the finer sediment grades outwards and deposits in a fan-shape away from the mountain face. The sediment is transported across a pediment into a closed basin where the bajadas grade back into a pediment, making the boundary difficult to distinguish. Bajadas contain playa lakes. Bajadas are common in dry climates where flash floods deposit sediment over time, although they are common in wetter climates where streams are nearly continuously depositing sediment
Alluvial fans are triangular-shaped deposits of water-transported material referred to as alluvium. They are an example of an unconsolidated sedimentary deposit and tend to be larger and more prominent in arid to semi-arid regions; these alluvial fans form in elevated or mountainous regions where there is a rapid change in slope from a high to low gradient. The river or stream carrying the sediment flows at a high velocity due to the high slope angle, why coarse material is able to remain in the flow; when the slope decreases into a plain or plateau, the stream loses the energy it needs to move its sediment. Deposition subsequently occurs and the sediment spreads out, creating an alluvial fan. Three primary zones occur within an alluvial fan which includes the proximal fan, medial fan, the distal fan. Alluvial fans can exist on a wide spectrum of size scale. For example, alluvial fans can be on the order of only a few meters at its base and can be as large as 150 kilometers with a slope of 1.5-25 degrees.
When numerous rivers/streams converge into a single plain, the fans can combine to form a continuous apron. In arid to semi-arid environments, this is referred to as a bajada and in humid climates the continuous fan apron is called piedmont alluvial fans; as a stream's gradient decreases, it drops coarse-grained material. It makes swagger of the channel and forces it to change direction and build up a mounded or shallow conical fan shape; the deposits are poorly sorted. This fan shape can be explained with a thermodynamic justification: the system of sediment introduced at the apex of the fan will tend to a state which minimizes the sum of the transport energy involved in moving the sediment and the gravitational potential of material in the fan. There will be iso-transport energy lines forming concentric arcs about the discharge point at the apex of the fan, thus the material will tend to be deposited about these lines, forming the characteristic fan shape. The sediment that results from erosion in elevated or mountainous regions flows into the primary streams in the region where the streams act as a drainage system and carries the sediment to the alluvial plain.
Due to the high degree of slope, the river/streams are classified as straight channels. Directly at the mouth of the feeder stream in the alluvial plain, the fan is narrow and is still subjected to high energy from the high degree of slope. Once the sediment exits the feeder stream, the sediment is no longer confined to the channel walls. With this unconfinement, the sediments begin to fan out; the alluvial fan becomes wider with increasing distance from the mouth of the canyon. When there is enough space in the alluvial plain for all of the sediment deposits to fan out without contacting other valleys walls or rivers, an unconfined alluvial fan develops. Unconfined alluvial fans allow sediments to fan out and the shape of the fan is not influenced by other topological features; when the alluvial plain is narrow or short parallel to depositional flow, the fan shape is affected. The biggest natural hazard on alluvial fans are floods and debris flows. Floods on alluvial fans are flash floods: they occur with little to no warning have high velocities and sediment-transporting capability, are of short duration.
Debris flows are a type of landslide, defined as a spatially continuous moving mass of water and material, composed of coarse debris. A modern occurrence of an alluvial fan is photographed in Figure 1 in the semi-arid region between the Kunlun and Altun mountain ranges that form the southern border of the Taklamakan Desert in northwest China; this particular fan is 60 kilometers in total length and is of significance because one part of the alluvial fan is still considered active. An alluvial fan is considered active when there is still a sediment source continually feeding the fan sediment. One portion of the fan has flowing streams that are continually depositing sediment and the fan is still prograding into the alluvial plain; the feeder channels consist of straight channels as well as instances of braided channels because of the large volume of sediment sourced from the local uplands. Various environmental and geologic factors exhibit control on the deposition of alluvial fan deposits; the primary factor in alluvial fan environments is sediment supply.
The sediment that comprise the bedload and suspended load of the regional streams is sourced from the erosion of the associated highlands in the area. Therefore, a high erosion rate corresponds to an increase in sediment in the streams which affects stream morphology. For example, a high sediment load is associated with braided streams entering and within the alluvial plain. Medium to low sediment loads in the feeder stream results in straight channels.4 Alluvial fans are built in response to erosion induced by tectonic uplift to create nearby mountain ranges/highlands. This uplift is necessary for a source of erosion where the sediments are deposited in an alluvial fan regime in the alluvial plain. Tectonics can affect the degree of stream gradients and cause changes in base level which may lead to incision into fan surfaces in the distal zone of the deposit. An increase in precipitation would allow a higher water level in the streams which would allow for a greater amount of sediment to be carried along with it to be deposited in the alluvial plain.
There are three primary zones, or facies, that exist within an alluvial fan deposit which include the proximal fan, medial fan, distal fan with an overal
The Piute Wash of extreme southeastern Nevada and northeast San Bernardino County California is the south-flowing drainage of the Piute Valley. The wash and valley are located northwest of California; the Piute Wash watershed and Piute Valley drain the eastern flank of the north-south Piute Range. The wash hugs the eastern portion of the Piute Valley, in the southeast of the valley, the wash skirts the west of the Dead Mountains traverses the southwest and south perimeter of the Dead Mountains descends steeply toward its outfall into the Colorado River in California adjacent Needles. I-40 descends steeply in this stretch down to Needles; the Piute Valley and Wash are north -- south trending as are the mountains bordering east. Southern portions of the wash receive some north flowing drainages from the north of the Sacramento Mountains. West of the western perimeter Piute Range of Piute Valley, the Sacramento Wash flows south, with the Fenner Valley in the northwest; the Sacramento Wash turns east to join the Piute Wash.
In the southwest a water divide separates the Ward Valley draining southwestwards into San Bernardino County. The Piute drainage is west of the Colorado Lake Mohave. A narrow drainage from the Newberry and Dead Mountains drain into the Havasu-Mohave Lakes Watershed. To the north of the Piute Wash watershed and Searchlight is the north-flowing Eldorado Valley, an endorheic basin that forms a dry lake. Cal-Nev-Ari, Nevada, is in the northern third of the valley; the elevation of Piute Wash outfall at the Colorado River, just north of Needles, is 488 feet. Watersheds Piute Wash Watershed, Nevada to California Las Vegas Wash Watershed