Our Dynamic Desert
Introduction to the Desert Landforms and Surface Mojave National Processes in the Mojave National Preserve Preserve and Vicinity Physiography
1 Weather By Philip Stoffer Data Open-File Report 2004-1007 General Mojave 2004 Geologic History ABSTRACT: Landscape features in the Mojave National Preserve are a product of ongoing processes involving tectonic Changing forces, weathering, and erosion. Long-term climatic cycles (wet Climates & and dry periods) have left a decipherable record preserved as Ancient landform features and sedimentary deposits. This website provides Lakes and introduction to climate-driven desert processes influencing landscape features including stream channels, alluvial fans, playas Weathering (dry lakebeds), dunes, and mountain landscapes. Bedrock & Erosion characteristics, and the geometry of past and ongoing faulting, fracturing, volcanism, and landscape uplift and subsidence Carbonate influence the character of processes happening at the surface. Rocks & Landforms Use of any traide, firm or product name is for descriptive purposes only and does not constitute endorsement by the U.S. Government. Granitic Rocks & Landforms U.S. GEOLOGICAL SURVEY Volcanic Rocks & U.S. DEPARTMENT OF THE INTERIOR Landforms 1Western Earth Surface Processes Team, Menlo Park, CA Faults & Active Tectonics
Pediments & Alluvial Fans
Stream Channel Development
Stream Terraces & Older
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Surfaces
Mojave River
Playas
Sand Dunes & Dust
Human Impacts
Selected References
3D Geology Tour
Index Page
Continue to the Introducation page.
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Introduction to the Desert Landforms and Surface Processes Mojave National in the Mojave National Preserve and Preserve Vicinity Physiography Weather Introduction Data Several hundred thousand people travel along Interstate 15 between Los Angeles and General Las Vegas every week, but typically less than one percent of these travelers venture off Mojave the main highway to spend time to view the desert scenery and to ponder its origin. Geologic However, even a brief stop will enchant visitors with the remarkable desert landscape. History This website is intended to provide basic geologic information about the origin of Changing landscape features throughout the Mojave National Preserve and surrounding region. Climates & The map below (Fig. 1) provides location reference to many of the landscape features Ancient referred to in discussions. Lakes
Weathering & Erosion
Carbonate Rocks & Landforms
Granitic Rocks & Landforms
Volcanic Rocks & Landforms
Faults & Active Tectonics
Pediments & Alluvial Fans
Stream Figure 1. Map showing the Mojave National Preserve and surrounding region. View a Channel larger version of this map. Development Many natural factors and processes are responsible for the development of landforms in Stream desert environments, particularly bedrock characteristics, and current and past climatic Terraces conditions and their changing plant communities. The landscape reflects the cumulative & Older effects of geologic forces or events that have transpired over many millions of years. Surfaces However, faulting, volcanism and erosion within the past million years, and particularly changing climatic conditions within the last 20,000 years, have had particularly strong
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Mojave effects on the physical appearance of the Mojave Desert landscape today. River This website provides basic discussions about the interplay of climatic factors with Playas geologic characteristics and history of the Mojave Desert region primarily focusing on the Mojave National Preserve. Follow the discussion (like a book) by clicking on the Sand Dunes "Continue to" links at the bottom of each page, or go directly to the selected sections by & Dust clicking any of the topical links on the left side of each page. Understanding regional climate history, physiography, and the physical characteristics and processes affecting Human earth materials are fundamental to interpreting the ongoing development of the Mojave Impacts Desert landscape and the ecosystem it supports. Follow the links to learn more about the Selected physical environment of the Mojave National Preserve and surrounding region! References To see a 3-D image tour of the Mojave National 3D Geology Preserve, click here. You will need red-and-cyan view Tour glasses. Most of the photographs within this website appear in 3D on this on-line geology tour at Index Page http://3dparks.wr.usgs.gov/moja/.
Continue to the Physiography page...
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Introduction to the Physiography Mojave National The Mojave Desert comprises the southwestern quadrant of the Basin and Range Preserve physiographic province, a vast region dominated by rugged mountain ranges and alluvium-filled basins that extends from northern Nevada to Mexico and from the Physiography California's Sierra Nevada and southern coastal region eastward to central Arizona and Utah. The Mojave Desert is transitional between the lower, hotter Sororan Weather Desert to the south and the colder high desert of the Great Basin to the north. The Data Mojave Desert is characterized by extreme variations in daily temperatures and General more arid conditions than other American desert regions. Freezing temperatures Mojave occur during the winter, particularly in higher elevation regions. Summers tend to be Geologic hot, dry, and windy. Average precipitation in the region is less than 12 cm, but is History highly variable from one year to the next. Almost all precipitation arrives in the winter, but the region also experiences rare, intense summer thunderstorms. It is Changing during these rare flood events that some of the most dramatic changes take place on Climates & the desert landscape. Ancient Lakes The Mojave National Preserve encompasses an eastern portion of the of the greater Mojave Desert ecosystem region. The Preserve consists of nearly 1.6 million acres Weathering of varied landscapes including rugged mountains, canyons, volcanic fields, alluvial & Erosion fans, dune fields, and dry lake basins. The U.S. Congress established the Mojave National Preserve in 1994 as part of the California Desert Protection Act. Carbonate Rocks & Elevations in the Preserve range from the highest point, Clark Mountain (elevation Landforms 7929 feet; 2417 m), to a lowest elevation at Soda Lake (932 feet; 284 m). Other high upland areas include portions of the Granite, Providence, and New York mountains. Granitic Ecological habitats vary with the landscape and precipitation: pinyon-pine forests Rocks & and frost-tolerant species occur above 5,500 feet (1675 m) where average Landforms precipitation is as much as 25 cm (some of which falls as snow); joshua-tree forests occur in the range of 4,000 to 6,000 feet (1220 to 1828 m); mixed desert shrub Volcanic communities exist in the middle elevation regions and along the mountain range Rocks & fronts, and; creosote bush and other drought-tolerant species survive in the lower Landforms elevation regions where rainfall averages less than 5 cm per year.
Faults & Active Mountains and Basins Tectonics Mountains impede travels across the desert, whether by pioneer wagon or sportscar. Pediments & Likewise, the mountain ranges delineate the landscape and serve as barriers to the Alluvial Fans migration of sediments (carried both by water and wind). Adjacent to each range are corresponding valleys that are filled with sediments. The Mojave Desert region is Stream within a great inland (isolated) drainage basin. Not for perhaps 10 million years Channel have rivers consistently drained to the ocean! During the past Ice Ages, great lakes Development filled many of the lower valleys; many of these lake basins overflowed into adjacent valleys, and some eventually spilled into Death Valley. However, as with the Stream current interglacial period, the region has dried up, leaving behind great dry Terraces lakebeds exposed to erosion by the wind. Between the ranges and the lakebeds are & Older regions covered by coalescing alluvial fans (called bajadas) or extensive flat regions Surfaces of barren, weathered bedrock (called pediments) where mountains probably once existed long ago but have long since worn away. The images below illustrate the
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Mojave "mountain and basin" character of the Mojave Desert region. River
Playas
Sand Dunes & Dust
Human Impacts
Selected References This zoomed-in view is looking southwest along the Interstate 15 3D Geology corridor from the top of Turquoise Mountain (just east of Baker, Tour CA). The view incompasses portions of Silver and Soda dry lakes (near Baker in the foreground), the Soda Mountains across the Index Page middle, and the large, distant Cave Mountain.
A high-altitude, oblique-view aerial photograph of the Mojave National Preserve region taken in September of 1968 with a view to the southwest. Note how the landscape is dominated by bajadas (coalescing alluvial fans) formed from the accumulation of sediments around erosionally dissected-mountain ranges. Ephemeral streams connect to dry lakebeds (playas) in the lowest valley regions.
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Cedar Wash cuts through a joshua tree covered landscape of a broad alluvial apron (a bajada) grading down slope from the Providence Mountains (left) to the main valley drainage, Kelso Wash (to the right). In the distance, Kelso Dunes blanket the valley beneath the distant high peaks of the Granite Mountains (upper left). Note the different color and texture of the broad wash - created by a different vegetation assemblage.
Historic climate data for the Mojave National Preserve is scarce; no single weather station fairly approximates conditions throughout the region. Click here to see weather data (seasonal temperatures, precipitation, and wind) for selected weather stations in the region.
Continue to Weather Data of the Mojave Region...
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Introduction Weather Data - Selected Reporting Sites In the Greater Mojave Region to the Mojave National Historic weather data for the Mojave National Preserve is relatively scarce because there are no significant population Preserve centers or airports in the vicinity where records were kept. The table below provides a summary of selected sites and data from in and around the greater Mojave region that might serve as a proxy for weather conditions in different Physiography settings within the national preserve (none of the sites are within the preserve itself). In the future data from many additional weather stations in the region will be available. Weather Data The weather data basically shows what any of the regional residents could tell you. The region has very hot summers and cool winters. Most of the rain falls in the winter months, but August typically has some monsoonal storms. Spring General tends to be the windiest season, and fall is the dryest and least windy season. Mojave Geologic History
Changing Climates & Ancient Lakes
Weathering & Erosion
Carbonate Rocks & Landforms
Granitic Rocks & Landforms
Volcanic Rocks & Landforms
Faults & Active Tectonics
Pediments & Alluvial Fans Blythe Daggett Death Eagle Mitchell Stream Location Barstow Bishop Channel FAA FAA Valley Mountain Caverns** Development Latitude N34-54 N37-22 N33-37 N34-52 N36-28 N33-48 N34-56 Longitude W117-02 W118-22 W114-36 W116-47 W116-52 W115-27 W115-30 Stream Elevation 2,162 4,108 268 1,922 -194 973 4,350 Terraces Temperature & Older Surfaces Degrees F January Mojave Maximum 60.0 52.9 67.6 60.7 65.3 64.1 54.4 River Minimum 31.7 21.4 38.2 35.9 39.6 44.1 36.9 Mean 45.9 37.2 52.9 48.3 52.5 54.1 -- Playas April Maximum 77.0 70.9 86.5 78.0 89.5 81.5 69.5 Sand Dunes Minimum 45.0 35.8 52.1 50.2 62.1 59.2 48.2 & Dust
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Mean 61.1 53.4 69.3 64.1 75.8 70.4 -- Human July Impacts Maximum 102.6 97.5 108.7 104.0 115.4 105.2 94.0 Minimum 67.2 56.3 76.8 73.2 88.4 82.8 71.1 Selected Mean 84.2 77.0 92.8 88.6 101.9 94.0 -- References October Maximum 83.0 77.1 90.7 83.2 92.9 87.5 75.1 3D Geology Minimum 48.1 37.4 56.1 54.6 62.9 64.6 54.4 Tour Mean 65.5 57.3 73.4 68.9 77.9 76.1 -- Annual Index Page Maximum 80.3 74.4 88.1 81.1 90.4 84.3 73.0 Minimum 47.7 37.6 55.4 53.2 63.0 62.4 52.3 Mean 64.0 56.0 71.8 67.2 76.7 74.3 -- Precipitation
Normals (IN) January .66 1.32 .44 .56 .27 .41 1.54 April .22 .31 .17 .27 .14 .14 .53 July .31 .19 .11 .32 .16 .41 .90 August .30 .11 .94 .50 .09 .56 1.80 October .19 .17 .32 .17 .11 .25 .73 Annual 4.14 5.61 3.75 3.81 2.03 3.26 11.82 Wind Speed
Average MPH January 7.1 6.5 8.6 April 10.1 8.9 13.8 July 8.3 9.4 12.2 August 8.4 8.8 11.4 October 8.1 6.7 9.5 Annual 8.4 7.8 10.9
Needles Palm Parker Thermal Twentynine Location Palmdale Randsburg FAA Springs Reservoir FAA Palms Latitude N34-46 N33-49 N34-35 N34-17 N35-22 N33-38 N34-08 Longitude W114-37 W116-32 W118-06 W114-10 W117-39 W116-10 W116-02 Elevation 913 411 2,596 738 3,570 120 1,975 Temperature
Degrees F January Maximum 62.9 69.3 58.6 63.9 53.8 69.8 62.7 Minimum 40.9 40.8 32.2 42.4 35.7 38.3 35.3 Mean 51.9 55.1 45.4 53.2 44.7 54.1 49.0 April Maximum 83.4 86.2 72.9 83.3 71.0 85.6 81.0 Minimum 56.3 52.2 42.6 58.7 45.6 55.1 48.5 Mean 69.9 69.2 57.8 71.1 58.4 70.4 64.7 July Maximum 108.7 109.1 97.7 107.8 98.8 106.9 105.4 Minimum 83.1 74.1 65.0 83.4 68.7 76.9 72.1 Mean 95.9 91.7 8.14 95.6 83.8 91.9 88.7 October Maximum 87.9 92.1 80.6 89.5 77.1 91.0 86.0 Minimum 61.1 57.9 47.4 64.4 53.2 57.8 52.7 Mean 74.7 75.0 64.0 77.0 65.2 74.4 69.6
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Annual Maximum 85.5 88.8 77.1 85.5 74.9 88.1 83.5 Minimum 60.1 55.8 46.4 61.9 50.4 56.7 51.8 Mean 72.8 72.3 61.6 73.9 62.7 72.4 67.7 Precipitation
Normals (IN) January .52 1.26 1.73 .78 1.23 .52 .42 April .26 .17 .53 .23 .40 .07 .12 July .47 .04 .04 .31 .12 .18 .67 August .67 .06 .23 .60 .16 .30 .68 October .35 .65 .16 .46 .20 .14 .26 Annual 4.39 5.20 7.38 4.97 5.48 2.82 3.89 Wind Speed
Average MPH January 6.6 8.8 5.0 6.1 April 10.3 12.9 8.3 9.9 July 9.7 12.0 7.0 8.1 August 8.9 10.8 6.2 7.5 October 8.0 9.2 5.9 6.0 Annual 8.7 10.6 6.5 7.6
Temperature and precipitation data from: NOAA, National Climatic Center (re-compiled by Gale Research Company, 1983, Climate Normals for the U.S. [Base: 1951-1980]: Detroit, MI.) **Mitchell Caverns, CA data reported from 1971 to 2000 from: http://www.ohwy.com/ca/w/wx045721.htm.
Wind data from: http://www.wrcc.dri.edu/htmlfiles/westwind.final.html - Western Regional Climate Center (Desert Research Institute and others; Reno, NV): The monthly average wind speeds are based on hourly observations from reporting airports and based on data from 1992-2002.
Continue to General Geologic History of the Mojave Region...
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Introduction General Geologic History to the Mojave National The oldest rocks exposed in the Mojave National Preserve are between 1.7 and 2.5 Preserve billion years old (early Proterozoic age). They consist of metamorphic rocks derived from pre-existing sedimentary, volcanic, and igneous intrusive rocks. Some of these Physiography rocks contain high-grade metamorphic minerals and textures consistent with having experienced pressures and temperatures typical of the lower crust between 12 and Weather 25 miles (20 and 40 km) below the Earth's surface. About 1.4 billion years ago, Data magmas intruded these older rocks (including the magmas that created the mineral deposits at Mountain Pass). Rocks similar to these form a basement complex General throughout the eastern Mojave region and throughout the Great Basin and beyond. Mojave Rocks of similar ages and characteristics crop out along the Colorado River in the Geologic Grand Canyon. The formed in association with a long period of mountain building History as smaller landmasses were gradually assembling to form the core of the modern continental landmasses. Changing Climates & Ancient Lakes
Weathering & Erosion
Carbonate Rocks & Landforms
Granitic Rocks & Landforms
Volcanic Rocks & Landforms Ancient metamorphic rocks (consisting of amphibolite schist and Faults & gneiss with granitic dikes and intrusions) are some of the oldest Active rocks in the region. This example is exposed in a streambed in the Tectonics western Providence Mountains. The rock hammer is about 30 cm for scale. Pediments & Alluvial Fans After about 1.4 billion years ago, the region that is now the Desert Southwest experienced little structural change, and erosion gradually wore down the landscape Stream to a nearly level plain, similar in character to the modern continental core of Channel Australia or the Canadian Shield region. A large "supercontinent" that had Development assembled earlier in time began to break apart, and a proto-Pacific basin began to develop. The edge of the North America continent gradually sank beneath the ocean Stream surface, and a thick sequence of sedimentary rocks began to accumulate on the Terraces continental margin (see "A" in figure below). The oldest of these sedimentary & Older deposits are over a billion years in age. These deposits formed from sand, mud, and Surfaces limey sediments deposited in shallow marine conditions, similar to the modern continental shelf around the Gulf of Mexico. This passive continental margin setting
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Mojave persisted for nearly 800 million years, starting in the late Proterozoic and lasting River through all of Paleozoic time (570 to 245 million years ago). The great carbonate- Playas rich (limestone and dolomite) sedimentary rock section (as much as 10 kilometers thick) preserved in the Mojave region is a testament that during this vast period of Sand Dunes time, North America had gradually drifted northward across the equatorial region, & Dust home to warm, shallow, continental platform seas teaming with shelly organisms (mostly algae and invertebrates). These carbonate rock formations today are home Human to many fossils. Impacts
Selected References
3D Geology Tour
Index Page
Generalized geologic history of the Mojave Desert region.
The thick sequence of late Proterozoic and Paleozoic sedimentary formations was folded and broken up by faulting that began with the formation of the Cordilleran range along the western margin of North America. Beginning around 250 million years ago, the great ancient supercontinent of Pangaea began to rift apart, forming the Atlantic Ocean basin. The North American continent gradually split away from
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what is now northern Africa and Europe. This relative-westward motion of the North American continent caused the western margin of the continent to change from being a passive to an active continental margin. The western margin of the continent began to override the adjacent oceanic crust beneath the Pacific Ocean (see "B" in figure above). Along with subduction of oceanic crustal uplift of the continental margin began, and erosion began to strip away the exposed rocks and sediments. Magma generated by subduction processes began to intrude upward, some of which reached the surface and erupted to form volcanoes. Beginning in the Jurassic Period, an extensive volcanic arc developed across the greater Mojave region. Deep below the surface, a series of great igneous intrusions (called batholiths) gradually became emplaced throughout the region. These igneous rocks (consisting mostly of granite) form the cores of the Sierra Nevada and many of the ranges throughout the Mojave region, including virtually every mountain range in the Mojave National Preserve. Great granitic intrusions formed in the Jurassic (170 to 140 million years ago) and again in mid-Cretaceous time (about 100 million years ago).
Intrusion and volcanism ended in the region in Late Cretaceous time. Erosion was the dominant process throughout the early part of the following Tertiary Period. Beginning around 30 million years ago (during late Oligocene time) new tectonic forces began to modify the landscape (Fig 6C). A great rift-style fault system developed across the region as the Great Basin began to spread apart. The formation of the Great Basin is analogous to the modern rifting that is going on in the Red Sea basin or the Great Rift Valley in Africa. The history of late Tertiary and Quaternary faulting and tectonism in the Mojave National Preserve is unlike any other geologic province in California. The tectonic framework for much of the Preserve is perhaps most similar to the Basin and Range-style structure of Arizona, but in contrast there are no deep basinal deposits and no big normal faults. Two detachment fault systems affected parts of the Preserve around 18 million and 14 million years ago. The Ivanpah Valley formed after 10 million years, probably as extentional bend in a strike-slip fault. Faulting is modifying the regional landscape, however, rather that basin-and-range-style faulting, fault systems active in the region today are associated with regional right-lateral shearing forces associated with the San Andreas Fault System, the Garlock Fault, and the Eastern California Shear Zone (all of these fault systems display measurable right-lateral displacements in the range of hundreds of kilometers). However, nearly all more recent Basin and Range-style tectonism is occuring well north of the Preserve. The character and movement activity of fault systems in Mojave National Preserve are under investigation to clarify times and amounts of displacement and the role in forming today's topography.
Throughout the Late Tertiary and Quaternary periods, large volcanic eruptions occurred fairly frequently in the Great Basin region. Volcanic ash blanketed the landscape, and many of these ash beds are preserved in the alluvial deposits that accumulated in the basins. Eruptions associated with the Cinder Cones and Lava Beds area within the Mojave National Preserve began in the Late Tertiary (around 7 million years ago) and has continued episodically through late Quaternary time (in the past one million years). The last volcanic episode in this area occurred only about 8,000 years ago.
Climatic changes during the last million years are largely responsible for most landscape features in the Mojave region today. In many ways, the character of modern alluvial fans, pediment surfaces, and playas, and the flora and fauna they support, reflect conditions that have evolved mostly within the past several thousand
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years. However, in addition to climate, the physical characteristics of these modern landscape features are tied to the properties of bedrock materials and tectonic history of any particular location.
Although somewhat out of date, Hewett (1956) provides a detailed bedrock geologic history with summaries of mineral resources and mines in the Mojave National Preserve region. A literature search will yield hundreds of references to scientific reports, articles, and field-trip guides about the region.
Contiume to Changing Climates & Ancient Lakes...
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Introduction Changing Climates and Ancient Lakes to the Mojave National The impact of both long-term and short-term climatic oscillations can be seen on the Preserve landscape. Glaciation periods lasting many thousands of years have happened repeatedly throughout the Quaternary Period. The last of these glaciation cycles Physiography ended roughly 15,000 years ago, and although glaciers did not form in the Mojave region, the overall wetter and cooler conditions that existed during glaciation periods Weather had an impact on weathering and erosion patterns in the region. Many questions Data about the impact of climate change on the desert environments remain unresolved, however casual observations demonstrate that climate changes are reflected by the General landscape. For instance, excavations into playas (dry lake beds) have yielded fossil Mojave remains of shelled invertebrates, fish, and plants that only could survive in perennial Geologic lake environments. Likewise, the giant sand dune fields that exist in the region today History likely could not have formed when wetter conditions persisted in the region. Persistent wetter conditions cause soil to form faster and allow plants to cover what Changing may otherwise be a barren landscape. These factors, in turn, reflect on how stream Climates & erode or deposit sediments on the landscape. The study of Quaternary lake sediments Ancient in the Mojave region has been the target of ongoing research for many decades. The Lakes climate-induced formation and disappearance of lakes in the Mojave region has also influenced the development of river drainage systems in the region over time, Weathering particularly of the Mojave, Owens, and Amargosa rivers drainages. These rivers are & Erosion now mostly ephemeral in nature, but during the wettest periods of the Ice Ages they were likely sizable rivers complete with a rich fauna and flora. Carbonate Rocks & Landforms
Granitic Rocks & Landforms
Volcanic Rocks & Landforms
Faults & Active Tectonics
Pediments & Alluvial Fans
Stream Channel Development
Stream Terraces & Older Surfaces
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Mojave River
Playas
Sand Dunes & Dust
Human Impacts This map show the location of major lakes and river in the Mojave region at the Selected close of the last Ice Age (late Pleistocene, about 15,000 years ago). At the peak of References the last Ice Age, the Lake Manix overflowed into Lake Mojave (which included both Soda Lake and Silver Lake basins). The Mojave River also flowed northward 3D Geology and merged with the Amargosa River before spilling into Lake Manley, the ancient Tour lake that filled Death Valley. The drainage system has also been postulated to have spilled over into the basins of Bristol Lake, Cadiz Lake, and Danby Lake before Index Page possibly flowing into the Colorado River drainage, but evidence for this drainage route has not been clearly resolved, partly because more recent alluvial sediments may cover the ancient stream channels. (Map modified after Blackwelder, 1954; note that the extent of the lakes shown here do not correspond to the maximum extent of lakes in the past. For examples, Lake Manix encompassed Coyote Lake and surrounding regions, and Lake Mojave encompassed more than the current Silver Lake and Soda Lake basins.)
Summary of Late Quaternary Climate History
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Below is a diagram that summarizes late Quaternary climate history based on analyses of sediments from ancient lakebeds in the Mojave Desert region. Investigations of 20th Century weather and stream flow data show the logical connection between increased precipitation and flooding, and lake development in the Mojave. According to Wells and others (1989), lake-forming climatic conditions occurred in 1916, 1938, 1969, and 1978. Wet, and possibly as important, seasonally cool conditions persisted during these years allowing shallow lakes to form in playa basins throughout the region. The regional climate during these years possibly emulates the more persistent wet and cooler climatic conditions that existed during the Ice Ages.
This diagram is a compilation of wet-to-dry cycles for the late Quaternary (based on multiple sources). Note that the time scale is not clearly resolved; it is likely that older wet episodes (glacial stages 4, 8, 12, 14, and older) were as variable as the youngest period (Stage 2). Resolution of stage 2 events is possible because, not only are these sediments youngest, and therefore least disturbed and best exposed, but they are young enough to be in an acceptable range for radiocarbon dating and other geochronology methods. Information was derived from articles within Enzel, Wells, and Lancaster (2003); [Geological Society of America Special Paper 268].
Climate-Induced Forcing Functions on Desert Landscape Processes
The impact of climate of the formation and disappearance of lakes in the Mojave
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region is relatively easy to visualize and interpret. However, climate-induced forcing impacts nearly all aspects of the biosphere and landforms in the region. For instance, wet periods not only allow lakes to form, but increased moisture over time will enhance plant growth (and range expansion), and soil development. With lakes and abundant plant cover, the sand supply to dune fields would likely be reduced. Conversely, when dry conditions return, the plant cover would eventually become reduced, and episodic desert storms would strip away soil (formed during the proceeding wet period), contributing to the influx of greater amounts of sediments downstream onto alluvial fans. Below is a generalized chart summarizing possible relationships of surface processes with climatic conditions.
Generalized linkage of climate-induced forcing functions on desert processes. Ongoing research is attempting to quantify short- and long-term effects of climate change on a host of surface processes affecting biota, landslide and debris flow hazards, dust and dune field changes, water table, water supply and quality, weathering & erosion rates, stream channel processes, alluvial-fan building, and probably many other factors that may have significance to human interests.
Continue to the Weathering and Erosion page...
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Last updated: December 18, 2009 (mfd)
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Introduction Weathering and Erosion in Desert Environments to the Mojave National Mountains form because, over long periods of time, uplift proceeds faster than Preserve erosion can keep pace. Through time, erosion progressively carves canyons into mountainous areas. Mountain stream channels are self-perpetuating; as water Physiography gathers into rills and channels, the greater the flow, the greater the erosive force. Likewise, streams with steep drainage profiles are capable of moving more material. Weather Data Without abundant water in the arid environment, the chemical breakdown of rocks proceeds extremely slowly relative to equivalent rocks in humid climates. However, General it is somewhat paradoxical that the mechanical breakdown of rock proceeds Mojave relatively quickly in the arid climate. In wet regions, the ground remains partially or Geologic fully saturated. Plants typically cover the landscape and bind the soil, and hence, History prevent erosion. In dry climates, soil forms very slowly, and much of the bedrock remains exposed to erosion. Physical forces in the desert that break down rocks Changing include the daily heating and cooling of rocks on the surface, expansion of plant Climates & root in cracks, the freezing and melting of ice in cracks, and exposure to wind and Ancient precipitation (particularly during storms). When rainfall occurs, particularly long- Lakes slow drenching rain, the mountain slopes become saturated. The added weight induces rock falls, landslides, and other forms of mass movement of material down Weathering slope. Even though rain falls infrequently in the desert, when it does rain large & Erosion quantities of sediment move down slope and into canyons entrained in flash-flood waters or as debris flows. A debris flow is a moving mass of rock fragments, mud, Carbonate soil, and enough water to keep the mass fluid. They typically travel at great speeds Rocks & down steep canyons, but may move slowly across a gentle surface of an alluvial fan. Landforms They can flow for great distances until the water they contain dissipates or separates from the alluvial material. Granitic Rocks & The churning action of flood waters or sediment-choked debris flows pulverize Landforms rocks into fragments (gravel, sand, silt, and clay). As rocks break into smaller and smaller fragments, the surface area of the resulting sediment volume increases. This Volcanic increase in surface area accelerates the chemical changes that convert feldspar and Rocks & other minerals in granite into clays. Soluble components in the rock dissolve and are Landforms carried away. With increasing distance away from mountain sediment source areas, the average size of rock fragments steadily diminishes and particles become Faults & increasingly round in shape. Active Tectonics
Pediments & Alluvial Fans
Stream Channel Development
Stream Terraces & Older Surfaces
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Mojave River
Playas
Sand Dunes A large granitic boulder and gravel deposits in the middle of the & Dust flood plain of a wash draining from the range hints at the power and intensity of flash floods or debris flows that episodically Human transport material from the Providence Mountains onto the alluvial Impacts fan. Hills that define the mountain front consist of older Selected Pleistocene alluvial fan deposits that accumulated when stream References base level was higher. Winter storm clouds hang over the Providence Mountains in the distance. 3D Geology Tour The character of the bedrock in mountain source areas plays a significant role in determining the character of sediments and soils in downstream areas (on pediment Index Page surfaces, alluvial fans, stream channels, and playa marginal areas), and the character of vegetation and fauna they support. Dominant rock types in the Mojave region include granite and ancient crystalline rocks, Paleozoic sedimentary rocks (mostly carbonates, limestone and dolostone), volcanic materials (mostly basalt), and reworked alluvial materials. Weathering and erosion of these types of bedrock produce the diverse and often unique landscapes in the Mojave region.
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Introduction Carbonate Rocks and Associated Landforms to the Mojave National In the Mojave National Preserve, carbonate sedimentary rocks of Proterozoic and Preserve Paleozoic age (consisting of limestone and dolostone) crop out throughout the Clark Mountains, the Mescal Mountains, in the northern Ivanpah Range, in the central portion of Physiography Providence Mountains, and elsewhere. Carbonate rocks originally form from limey sediments consisting of the calcareous skeletal remains of algae and invertebrate shell Weather material or precipitates directly from agitated, warm seawater (as on a shallow continental Data shelf in a warm climate). Most ancient limestones formed from planktonic algae, but in late Paleozoic time coralline reefs became significant producers of carbonate sediments. General Limestone consists dominantly of the mineral Calcite-CaCO3, whereas dolostone consists Mojave dominantly of the mineral dolomite-CaMg(CO3)2. Dolomite is typically a secondary Geologic mineral replacement of original calcite material. Ancient carbonate rocks like those in the History Mojave region tend to be enriched in dolomite. Below are examples of common fossiliferous carbonate rocks of Paleozoic age from the Mojave region. Changing Climates & Ancient Lakes
Weathering & Erosion
Carbonate Rocks & Landforms
Granitic Rocks & Landforms Oncolites (algal limestone balls) float in a carbonate-mud matrix in the Cambrian-age Chambless Formation. This easy-to- Volcanic recognize oncolite-bearing limestone formation crops out in many Rocks & areas throughout the Mojave National Preserve region. These Landforms nearly spheroidal oncolites formed by algae and/or cyanobacterial growth in shallow warm marine waters of a carbonate platform Faults & environment. Active Tectonics
Pediments & Alluvial Fans
Stream Channel Development
Stream Terraces & Older Surfaces
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Mojave A boulder of a fossiliferous limestone displays stromatoporoids River and corals of early Devonian age (Sultan Formation). Boulders like this one are not uncommon in alluvial fans downstream from Playas the Paleozoic age sedimentary rock belt exposed in the Providence Range. Sand Dunes & Dust
Human Impacts
Selected References
3D Geology Tour
Index Page
An expansive Joshua-tree forest covers a pediment surface (along Cima Road). In the distance, steeply dipping and folded sedimentary rocks (mostly limestone and dolomite) of late Proterozoic and Paleozoic age crop out throughout the Mescal Range.
In contrast to other types of rocks, carbonate rocks tend to be fairly resistant to erosion in arid climate conditions. The ancient carbonate rocks in the Mojave region are typically both dense and brittle and tends to be heavily fractured at the surface. At depth, fractures in carbonate tend to heal over time as the rock gradually flows under extreme pressure, and as calcite and other minerals precipitate in crevasses over time. Throughout the desert southwest, deep canyons carved into carbonate rock display collapse breccia, which are massive surficial deposits that consist of broken fragments of limestone and dolostone tightly cemented in a carbonate matrix.
A small cavern occurs in brecciated carbonate rocks that crop out along an unnamed wash draining from the western Providence Mountains (8 miles directly east of Kelso Depot). "Collapse breccias" like this are prevalent in the Bonanza King Formation. This formation is nearly 300 meters thick and consists of algal limestone and dolomite of Middle Cambrian age (around 550 million years). The age of the "collapse" is unresolved, but may actually be an active physical-chemical process that affects large carbonate units in the desert surface environment. They may actively be "flowing" down slope under the force of gravity. This breccia is probably an early Quaternary-age landslide deposit that has been
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reconsolidated (cemented) by groundwater interaction with the carbonate rock.
Carbonate rocks dissolve in freshwater, with calcite being more soluble than dolomite. With each precipitation event, traces of carbonate material will dissolve and migrate with flowing water. Dissolution occurs along fractures in the subsurface producing caverns. As water evaporates at the surface, calcite will precipitate again, cementing sediments on alluvial fans to form a durable calcareous crust (called caliche). Calcite is a major component of playa mud deposits. Varieties of freshwater limestone deposits called tufa and travertine form around springs and in former wave-influenced lake shore zones. In caverns, travertine deposits are called speleothems (which include stalagmites, stalactites, columns, flowstone, and other features).
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Mitchell Caverns in the Providence Mountains State Recreation Area has been developed for commercial visitation. The cavern formed in limestone of Late Paleozoic age (Pennsylvanian- and Permian-age Bird Springs Formation). The cavern formed long ago when the bedrock was constantly exposed to groundwater, allowing dissolution of the limestone to occur. Today, the cavern is high and dry; it is more than 500 meters above the valley floor and a constant supply of groundwater.
Travertine tapestries, flowstone, and other speleothems gradually form where groundwater enters the cavern and evaporates, leaving behind calcium carbonate. Features like this one probably took many thousands of years to form. Only a small percentage of the speleothems in Mitchell Caverns are actively forming.
In the Mojave region, alluvial deposits derived from areas with carbonate bedrock tend to consist of blocky, unevenly sorted sediments. In many areas chert layers and metasandstone layers occur interbedded within the bedrock. These more siliceous materials tend to be more resistant to both mechanical and chemical weathering forces, and as a result, alluvial surfaces and sediments down slope from carbonate rock source areas tend to be enriched in these associated siliceous materials. Carbonate mountains are the highest and steepest without exception. These areas are prone to stronger flood forces, bigger canyons, more precipitation, coarser fans, steeper fans, and hense, greater risk for debris flow activity.
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Introduction to the Granitic Rocks and Associated Landforms Mojave National Weathering and erosion in arid regions underlain by granitic bedrock produce Preserve unique characteristic landforms. Spheroidal weathering is a form of chemical weathering in which concentric shells of decayed rock (ranging from a few Physiography millimeters to a couple meters) are successively loosened and separated from a block of rock. In the subsurface, groundwater penetrates along fractures and causes Weather the chemical breakdown of rock along surfaces. Sharp corners at the intersection of Data fractures tend to break down first. In this manner, blocks of granitic bedrock (or other rocks that do not have layers or bedding) tend to become rounder as General weathering proceeds. In humid regions, spheroidal weathering of granite typically Mojave occurs in the subsurface. In contrast, in arid regions the rate of chemical weathering Geologic is slow relative to the rate of surface erosion. As a result, in granitic terrains knob- History shaped outcrops and spheroidal blocks accumulate on the surface. In the Mojave region, granite typically breaks down to form fairly uniform quartz- and feldspar- Changing rich, coarse-sandy sediment compared to other rock types. In addition, many of the Climates & major pediment areas in the Mojave National Preserve have granitic bedrock. This Ancient is probably directly related to the more-or-less uninform weathering and erosion Lakes characteristics of large, homogeneous granitic intrustions. Weathering & Erosion
Carbonate Rocks & Landforms
Granitic Rocks & Landforms
Volcanic Rocks & Landforms
Faults & Fractured granite bedrock is exposed along Globe Wash in the Active Providence Mountains. Tectonics
Pediments & Alluvial Fans
Stream Channel Development
Stream Terraces The characteristic rounded boulders and knob-shaped outcrops & Older throughout the Granite Mountains formed as a result of spheroidal Surfaces weathering and erosion of fractured granite.
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Mojave River
Playas
Sand Dunes & Dust
Human Impacts
Selected References
3D Geology Large granitic intrusions of Cretaceous age are the bedrock of Tour Kessler Peak in the southern Ivanpah Mountains. A Joshua-tree forest blankets a pediment surface in the foreground. This view is Index Page along Cima Road east of the Teutonia Mine area.
Continue to the Volcanic Rocks and Associated Landforms page...
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Introduction Volcanic Rocks and Associated Landforms to the Mojave National Preserve
Physiography
Weather Data
General Mojave Geologic History
Changing Climates & Ancient Lakes Examples of landform features associated with modern and ancient volcanism. Weathering A volcano forms at an site where erupted material builds up (including lava & Erosion flows, cinders, and ash). Over time, weathering and erosion break down and strip away surficial materials, leaving behind remnants of volcanic rock that Carbonate chilled below the surface (including plutons, dikes, sills, and laccoliths). A Rocks & pluton is a deep-seated igneous intrusion. A stock is a remnant of the vent of a Landforms volcano or plutonic body with an areal extent less than 40 square miles (or 100 square kilometers). Far below the surface, a large magma chamber will slowly Granitic cool to form small plutons and large batholiths. A dike is a place were molten Rocks & material cooled in a vertical crack. Sills form when molten material squeezes Landforms between horizontal layers. An escarpment that forms when erosion exposes a sill is call a palisade. A laccolith is a blister-shaped intrusion. Volcanic Rocks & Evidence of past volcanism can be seen throughout the Mojave Desert region. Landforms Within the Mojave National Preserve, two notable areas that display volcanic rocks and associated landforms include the Cinder Cones and Lava Flows National Faults & Natural Landmark Area (which encompasses many Quaternary-age volcanoes) and Active the Hole-in-the-Wall area (a more ancient volcanic area). Other areas of extensive Tectonics volcanic rocks are the Piute Range and Pinto Mountain.
Pediments & Cinder Cones and Lava Flows National Natural Landmark Area Alluvial Fans
Stream Volcanic eruptions have occurred many times throughout the Mojave National Channel Preserve in the geologic past; the most recent eruption in the region was about Development 8,000 years ago. Many of the youngest volcanic features in the Cinder Cones and Lava Flows area have changed very little since lava last erupted. Plants Stream communities have not yet become established on younger cinder cones and lava Terraces flows. Recent volcanic cones and lava flows are easy to recognize. The cooled black & Older lava rock is called basalt. In many places, the surface of these flows still preserves Surfaces the fluid texture created by flowing lava. Blocks and pieces of frothy lava rock (called cinders) piled up around places where molten material reached the surface, producing cinder cones. http://pubs.usgs.gov/of/2004/1007/volcanic.html[2/21/2014 3:45:50 PM] Our Dynamic Desert
Mojave River
Playas
Sand Dunes & Dust
Human These three cinder cones are in the Cinder Cones and Lava Beds Impacts area. Eruptions in this volcanic field occurred over the last several million years. Successive eruptions and flows have blanketed Selected older flows. In some cases, lava flowed on the surface for as much References as 10 kilometers from the eruption site. 3D Geology Tour
Index Page
A nearly perfect cinder cone in the Cinder Cones and Lava Beds Natural Landmark Area in the north-central portion of the Mojave National Preserve. Notice rills and gullies that are slowly degrading the cone.
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A lava tube forms where the surface of a lava flow cools, but lava continues to flow below the surface. In this example in the Cinder Cones and Lava Beds area, the surface layers of basalt lava have collapsed, creating an entrance to the lava tube. More cinder cones are in the distance. Note the rubbly, rough lava flow surface.
View of the inside of a lava tube in the Mojave National Preserve. Natural skylight shines on the dust-covered floor and provided reflected light throughout the short passage of this lava tube.
The Hole-in-the-Wall Volcanic Area
Evidence of older volcanic eruptions is found throughout the Preserve. Massive eruptions, larger than perhaps any eruption recorded in historic times, occurred in the vicinity of Hole-in-the-Wall. Geologists have determined that massive eruptions began in that region around 18.5 million years ago, and continued for several million years. Massive explosive-style eruption blanketed the region with molten or near molten debris. In places where these rocks are still preserved, individual beds (consisting mostly of rhyolite tuff) approach several hundred feet in thickness. Rhyolite is a volcanic rock that has a mineral composition similar to granite, but most crystal grains are too small to see. Tuff is a textural name for a volcanic rock formed from an agglomeration of volcanic particles or rock fragments that may be tightly cemented or "welded" (due to heat from the eruption). Clouds of volcanic ash from these eruptions probably blanketed the entire Great Basin region and beyond. With time, however, most of the volcanic material ejected from these eruptions has long since eroded away.
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View looking north toward the volcanic rocks (consisting of ash beds and lava flows) of Hole-In-The-Wall (left foreground) and Table Top Mountain (distance).
Tafoni is a type of surface weathering caused by wetting and drying of porous rocks that gives these cliffs of rhyolite tuff a "cheese-like" appearance (located in the canyon below the campground at Hole-In-The-Wall).
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Weathering and erosion of tuff forms hoodoos (irregularly-shaped rock spires) along Wild Horse Canyon near Hole-In-The-Rock.
In the past, massive explosive volcanic eruptions (called ignimbrites) produced thick blankets of volcanic tuff that covered large portions of the Mojave region. In places these ignimbrite deposits and other more fluid lava flows mantle topography, preserving past landforms. A pediment is preserved at Cinder Cones, and ancient hills and pediments are preserved near Hole-In-The-Wall. Ignimbrite deposits are dense and tend to resist weathering and erosion. As a result, they tend to focus stream flow around hem, forming narrow channelized canyons. This can be seen in drainages from the New York Mountains through Lanfear Valley to Fenner Valley. This channel development pattern can also be seen along lava flows in the Cinder Cones area. Dry water falls occur where streams drain coming off the volcanic flows into the more easily eroded alluvial sediments surrounding the volcanic field.
In contrast, cinder cones degrade relative quickly compared to the lava flows. In a study of erosion rates of volcanic materials in the Cinder Cones region, Dohrenwend and others (1984) found that the oldest remains of cones were only about 1 million years old, whereas the older flows were about 3 million, and the remains of stock edifices were as old as 7 million years.
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Last updated: December 18, 2009 (mfd)
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Introduction Faults and Active Tectonics to the Mojave National Evidence of faulting can be seen throughout the Mojave region. Faults range in Preserve scale and complexity from small, simple offset measurable in inches or feet to massive thrust faults, normal faults, and strike-slip faults that have displacements Physiography ranging upward to tens of miles or more. The timing and rate of displacement along faults is highly variable. Many regional fault show evidence of activity that extend Weather back into Precambrian, Paleozoic, and Mesozoic time. Faulting in early to middle Data Tertiary Period is largely responsible for the mountainous relief in the Mojave Region, although faulting activity in the late Tertiary through to the present is General actively influencing landscape development. Some faults formed in association with Mojave volcanic activity. Geologic History As the Landers earthquake of 28 June 1992 (magnitude 7.3) demonstrates, the region is seismically and tectonically active. The epicenter of the Landers Changing earthquake was about 50 miles east of the Mojave National Preserve. The Climates & earthquake presented a surface rupture over 40 miles long (75 km). Ancient Lakes
Weathering & Erosion
Carbonate Rocks & Landforms
Granitic Rocks & Landforms
Volcanic Rocks & Landforms
Faults & Active This map of the Mojave National Preserve region shows the Tectonics location of known and inferred faults with activity ranging that display either late Quaternary displacement activity (in the past Pediments & 600,000 years - shown in red), or faults that show slightly older Alluvial Fans activity (roughly 600,000 to about 3 million years - shown in yellow). Older faults, which are abundant, are not shown. For a Stream larger verion of this map, click here. Channel Development Fault movement influences the landscape by uplifting barriers to stream or wind flow, which in turn influences the patterns of sediment movement and deposition. Stream Fault activity influences the geometry of mountain fronts and the development of Terraces basins. Faults activity during the Quaternary influenced the location and & Older development of lakes (and playas during the dry periods), and influenced the Surfaces location of dune field development. Faults also serve as pathways of fluid migration. Desert springs are typically associated with fracture in rocks. Also, many
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Mojave mineral resource prospects in the region are related to the implacement of magmatic River fluids or ore-mineral precipitates along fault and/or fracture zones. Playas
Sand Dunes & Dust
Human Impacts
Selected References
3D Geology Tour
Index Page
This view is looking west into the Badlands of eastern Lanfair Valley. A stream has carved a valley into Piocene and Quaternary basin-fill deposits. In the distance the stream leaves the sedimentary basin fill and enters a canyon carved into middle tertiary basalt flows of the Piute Range. A major north-to-south trending fault defines the western side of the Piute Range at this location. It is likely that canyon is actively forming as the Piute Range is gradually rising along this fault zone. The red basin-fill deposits do not contain volcanic material derived from the adjacent volcanic rocks. This suggests that this fault system is relatively young and may be still actively developing.
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Introduction Pediments and Alluvial Fans to the Mojave National The term, mountain front, is an imaginary borderline between a mountainous area Preserve and a low, gently dipping plain (either a pediment or alluvial fan). A pediment is a gently sloping erosion surface or plain of low relief formed by running water in arid Physiography or semiarid region at the base of a receding mountain front. A pediment is underlain by bedrock that is typically covered by a thin, discontinuous veneer of soil and Weather alluvium derived from upland areas. Much of this alluvial material is in transit Data across the surface, moving during episodic storm events or blown by wind.
General Mojave Geologic History
Changing Climates & Ancient Lakes
Weathering & Erosion
Carbonate Rocks & Landforms Granite exposures and rounded boulders shaped by spheroidal Granitic weathering crop out on the pediment surface blanketed by a the Rocks & high Mojave desert mixed juniper and Joshua-tree forest in the Landforms vicinity of Teutonia Mine along Cima Road.
Volcanic Pediment-forming processes are much-debated, but it is clear that rocks such as Rocks & granite and coarse sandstone (and Tertiary conglomerate made up of boulders of Landforms these rocks) form virtually all pediments in the Mojave Desert. These rocks disintegrate grain-by-grain, rather than fracturing and then being reduced in grain Faults & size by alluvial transport processes. Active Tectonics Alluvial fans are aggrading deposits of alluvium deposited by a stream issuing from a canyon onto a surface or valley floor. Once in the valley, the stream is unconfined Pediments & and can migrate back and forth, depositing alluvial sediments across a broad area. Alluvial Fans View from above, an individual deposit looks like an open fan with the apex being at the valley mouth. Typically the fans formed by multiple canyons along a Stream mountain front join to form a continuous fan apron, termed a piedmont or bajada. Channel Development
Stream Terraces & Older Surfaces
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Mojave River
Playas
Sand Dunes & Dust
Human Impacts Aerial view of Lucy Gray Fan, an alluvial fan that radiates from a Selected canyon cutting through the Lucy Gray Mountains and drains into References the Ivanpah Valley (north of the Mojave National Preserve in 3D Geology Nevada). Below the mouth of the canyon the stream divides into Tour several channels. Active channels (void of vegetation) appear white, whereas, darker areas on the fan are covered with Index Page vegetation and possibly a thin veneer of soil. Channels migrate as they become choked with sediment as flood waters seep into the ground. Coarser rock fragments remain high on the fan, whereas finer materials (sand, silt, and clay) will continue to migrate downslope. Only during more intense storms will water reach and pond on the Ivanpah playa.
Large areas within the Mojave Desert are pediment surfaces. These pediments reflect both the antiquity of some mountain structures in the region and the persistent arid climatic conditions in the region. Perhaps the most notable pediment in the region is Cima Dome, a very broad, shield-shaped upland area within the Mojave National Preserve (below). This great, gently-sloped upland area represent a region where desert-style weathering and erosion has stripped away most of the relief to the point that the erosion keeps pace with surface weathering and that surface gradient is gentle enough to prevent gully-style downcutting. Isolated rocky hills or knobs that rise abruptly from an erosional surface in desert regions are called inselbergs.
The broad, gradual arch of Cima Dome is a mature pediment surface broken by relatively small "rock islands" (inselbergs). Teutonia Peak is the small peak to the left of the high point on Cima Dome. This view is from along Cima Road, about five miles (8 kilometers) south of Interstate 15. The flat plain in the foreground is also a pediment with a thin veneer of alluvium. http://pubs.usgs.gov/of/2004/1007/fans.html[2/21/2014 3:46:11 PM] Our Dynamic Desert
This view from the top of Teutonia Peak faces north over the northern flank of Cima Dome. Rock knobs of spheroidal- weathering granite bedrock rise above the pediment surface that consists of barren weathered granite bedrock covered with a thin intermittent veneer of sediment and soil. This expansive pediment surface probably extends to the flank of the mountains in the distance. (This is looking back toward the foreground area shown in the image above.) Rock underlying Teutia Peak is Jurassic grainite, which generally does not form pediments; adjacent pediment-forming rock of Cima Dome is Cretaceous in age.
Pediment domes and islenbergs define the landscape in the central portion of the Mojave National Preserve. This view faces north from an alluvial fan draining the Providence Mountains towards the pediment dome upland region of the Marl Mountains. Kelso Wash is the axial trunk stream in the middle of the valley. In the foreground, a relatively stable alluvial fan surface consists of desert pavement broken by braided stream channels and a patchwork of vegetation (mostly white bursage [gray] and creosote bush [green]). Total surface relief in this lower portion of the fan is in the range of one meter.
The development of pediments and alluvial fans is progressive with the uplift of mountains and subsidence of adjacent basins. Pediments reflect a relative "static equilibrium" between erosion of materials from upland areas and deposition within an adjacent basin. The slope of the landscape is gentle enough that weathering and transport of sediments from upland areas and the pediment that no significant stream incision occurs. In many areas throughout the Mojave region it is nearly impossible to see where a pediment ends and alluvial fans begin, however, geophysical data and water-well drilling shows that in many places sediment filled basins do occur
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adjacent to pediment areas.
The impact of climate change on alluvial fans has been the focus of much research. Studies show that a period of elevated alluvial fan deposition occurred between the time of the Last Glacial Maximum (about 15,000 years ago) and the beginning of arid conditions in the early Holocene (about 9,400 years ago). McDonald et al, (2003) suggest that the climatic transition from seasonable wet conditions to arid conditions, punctuated by extreme storm event (possibly associated with tropical cyclones) may be responsible for this change. Today, heavy rainfalls rarely provide enough precipitation to allow enough surface runoff to occur on highly porous soils and colluvium. Only during major stream event will water discharge in volume and intensity to move material from mountain source areas to lower fan areas. In addition to extreme storm events,the buildup of alluvial fan deposits at this Pleistocene/Holocene time transition may be linked with the transition from widespread plant cover to the more barren character of the modern Mojave landscape. Die-back of plants would decrease rooting, making more mountain-side material available for erosion and transport to alluvial fans.
Continue to the Stream Channel Development page...
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Introduction Stream Channel Development to the Mojave in the Changing Mojave Climate National Preserve Progressive landscape development in any particular area is a function of many factors including climate (precipitation and seasonal weather patterns), vegetation, Physiography slope and drainage topography, bedrock character, tectonic history, and possibly other factors. Interpreting the history of a landscape (or modeling its future) is Weather difficult without a measure of these different variables, and their changes through Data time. However, as our collective knowledge of past climatic conditions and geologic history of the Mojave region progresses, patterns in observation begin to General emerge that can be modeled. Below is a geomorphic model of stream channel Mojave development for roughly the past million years for the Mojave region (but can be Geologic applied elsewhere). The diagram illustrates an idealized cross section of an alluvial History surface where the progression of stream down cutting and infilling resulted in the Changing development of channels and terraces (incised flood plains); youngest to oldest from Climates & left to right. The model incorporates observations from the field with knowledge Ancient gained from climate history investigations in the region. Lakes
Weathering & Erosion
Carbonate Rocks & Landforms
Granitic Rocks & Landforms
Volcanic Rocks & Landforms This geomorphic profile shows interpretation of the relative ages and character of Faults & Quaternary alluvial channels and terrace deposits in the Mojave region (Dave Active Miller, USGS; to see a larger version of this image, click here). Note that no Tectonics vertical elevation is applied. Typically the greatest elevation differences between active channels and older terrace deposit occur high on an alluvial fan and may Pediments & range measurably by tens of meters. Low on alluvial fan the differences between Alluvial Fans oldest and youngest deposits may be less than a meter.
Stream Qya1 - "Quaternary young alluvium" (Qya); the "Qya1" represents an active stream Channel channel and its deposits; the channels tend to be void of vegetation and display Development evidence of recent stream flow activity.
Stream Qya2 - represents older flood plain surfaces that have not been disturbed by Terraces flooding long enough for plants to become established.Qya2 surfaces typically have & Older the greatest biomass of all surfaces. This is probably a combination factors: roots Surfaces can take advantage of the loosely consolidated deposits and access to moisture at depth. As roots stabilize the Qya2 surface flood overbank fines can allow for
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Mojave increased moisture retention. River Qya3 & Qya4 - represents mid- to older-Holocene alluvial fan surficial deposits Playas that are elevated and isolated from active channel erosion. These surfaces have a thin, intermittent soil, often with accumulation of floodplain overbank deposits and Sand Dunes wind-blown silt deposits on surfaces that have not experienced significant erosion. & Dust These surface are generally sparsely vegetated relative to Qya2 surfaces.
Human Qia1, Qai2, & Qia3 - represent progressively-older, late Pleistocene age deposits Impacts and surfaces that range in age from about 20,000 to 400,000 years. These deposits and surfaces possibly correspond to cycles of aggradation and erosion in Selected conjunction with alternating wet and dry climatic cycles in the Mojave region References during the late Pleistocene. Older surfaces of Qia type tend to be barren of plants relative to the younger Qya surfaces, and may have well-developed desert pavement 3D Geology that may cap a thin silty, loam soil (vesicular A horizon) that overlies a more Tour weathered, dense clay-rich subsoil (Argillic B horizon). Qai1 to Qai3 surfaces tend to be best preserved in the middle portion of "stable or well-developed" alluvial Index Page fans, or occur as elevated bench-like terraces along stream channels with broad valleys.
Qoa - represents middle Pleistocene and channel deposits and terraces that are roughly older than 400,000 years. These deposits are typically highly eroded, and are locally represented at rounded hills consisting of tightly cemented (caliche) alluvial gravels or paleosols (ancient soils horizons), typically along the range front of mountains. In Qoa deposits, the sediment's cement is dominantly calcium carbonate precipitated from meteoric (atmospheric water) and groundwater in the past, but the process is ongoing. In desert conditions, infrequent rains dissolve calcium carbonate from the upper soil, and carries dissolved components downward. The accumulation of calcium carbonate through plant transpiration processes creates an impenetrable caliche (calcic horizon) in the lower subsoil. In some places, the calcium carbonate and other mineral precipitates may have been contributed by migrating groundwater. Older Pleistocene and late Tertiary deposits have long since been eroded away in the Mojave region, or are locally incorporated in older basin-fill deposits; there is generally no surface expression remaining for these older deposits/features.
Stream Channel Processes
Even in the mountainous regions most streams flow only during or shortly after storms. Perennial water only flows in groundwater discharge areas associated with springs in a few mountain canyons, in Afton Canyon where the regional groundwater table intersects the canyon bottom, and a few other springs. In most areas within the Mojave region, streams will flow only after long periods of steady rain, typically during a wet winter. The periodicity and intensity of such rain events depends on elevation, but in the lower regions historically floods may only happen in intervals measured in several years to decades. To see the history of flood frequency in the Mojave region over the 20th Century see the on-line report by Hereford and Webb, (2000).
Floods produce the visually definable channels in streambeds (active channels). When water is not flowing in the stream between storm events, an active channel typically consists of sand, gravel, dried mud, or barren bedrock. Cut and fill sediment bedforms appear relatively fresh (where not trampled by animals, including humans). Flowing water strips away vegetation, moves sediment, and
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reconfigures bedforms in the channel. Sediment character and supply, slope, and flow volume and duration are controlling factors that defines the size of stream channels and the character of sediment found in the barren channel once a flood event is over. In canyons above the mountain front, stream channels are typically filled with angular rock fragments ranging from coarse sand to great boulders, with rapids or falls occurring where bedrock is exposed in the stream channel. Larger floods can scour the channel clear of sediments, whereas lesser flood events can contribute to the backfilling of channels. Backfilling is most evident to desert travelers who frequently travel the same stream beds year after year. In one year a stream bed in mountainous area may be easily passable by vehicle, but the next year the wash is inaccessible because finer materials between larger boulders may have vanished due to an erosion event. Later, the fine deposits between boulder may reaccumulate after a different storm event. These changes reflect the differences in duration, spatial patterns, and intensity of individual storm events affecting a drainage basin.
Downstream of a mountain front streams deposit sediments on alluvial fans, and in in the more upland areas, the channels on the upper alluvial fan may go through periods of down cutting, infilling, and channel migration. Typically the size and depth of the channel, and the size of the rock fragments diminish in size down slope and away from the mountain front. In the mid to lower fan area, stream channels typically diminish to depths less than a meter, and sediment consists of fine gravel and sand. In most areas, a trunk stream defines the main drainage between coalescing alluvial fans, or playas (dry lake beds) may exist were topographic barriers impede the flow of surface water from a drainage basin.
Examples of Stream Channel Features
This image shows is a view of an upper fan area in the western Providence Mountains. The "active channel" on the left (Qya1), and another less active, higher channel on the right that only receives water during the most intense flooding events (Qya2). Mature, or well-established, vegetation populates parts of the flood plain that generally does not receive flash flood waters (Qya3 and Qya4). The yellowish plant is cheesebush, a plant adapted to rapid colonization of disturbed surfaces and common in washes.
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This view looking west from the mountain front of the Providence Mountains looking down a wash that has incised into older (Pleistocene) alluvial fan deposits. The wash continues down slope and eventually merges with the actively aggrading surface of the lower fan closer to the axial trunk stream (Kelso Wash) that drains the fan aprons draining from the Providence Range and the Kelso Mountains. Note the diverse plant community on the high surface in the foreground.
Cedar Wash is the main channel draining the northern Providence Mountains region. The break in slope along the Holocene stream valley is marked by a vegetation change between the Joshua-tree forest on the slopes, and the desert scrub-covered sandy gravel of the flood plain. The barren active channels on the modern flood plain stand out as tan lines. Down cutting by Cedar Wash into older Quaternary alluvial fan deposits has created a well- developed terrace along the valley. This down cutting probably occurred during the wetter regional conditions associated with the last glaciation period that ended roughly 15,000 years ago. With the dry conditions that exist today, the valley is gradually filling in with alluvium because the stream can no longer move sediments faster than they accumulate.
Continue to the Stream Terraces and Older Surfaces page...
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Introduction Stream Terraces and Older Surfaces to the Mojave National Stream terraces form when streams carve downward into their floodplains, leaving Preserve discontinuous remnants of older floodplain surfaces as step-like benches along the sides of the valley. Stream terraces are common throughout the Western United Physiography States. In the context of this discussion on the Mojave region, older surfaces represent flattened areas (plateaus, mesa, uplands areas, hillside benches) that are Weather stable or isolated, neither experiencing significant rates of sediment buildup Data (aggradation) or down cutting by erosion. These older surfaces may have no clear or obvious connection to a more modern drainage system in a particular area. Terraces General and older surfaces preserve or display unique characteristic soil profiles or Mojave weathering characteristics because of their long-standing isolation from stream Geologic erosion. History Many factors influence why streams episodically carve into their floodplains, Changing forming stream terraces. Because stream terraces are typically widely distributed Climates & along steams throughout a region, changing climatic conditions are likely a most Ancient important contributing factor to their formation. Streams broadened their floodplains Lakes when sediment supplies are high and down cutting by stream erosion is abated. In cool, wet periods, plants typically cover the landscape, and hence sediment supply Weathering is low; enhanced moisture increases stream flows, and streams draining & Erosion mountainous regions will cut downward. During dry periods, plants don't provide enough cover to prevent intense erosion during infrequent storms. As a result, high Carbonate sediment yields may result in the backfilling of stream channels. This natural Rocks & feedback system is much more complex than this because many other processes Landforms occur simultaneously. Under cooler, wetter conditions during an ice age, soil development and weathering processes proceed faster due to more frequent wetting Granitic and drying, more freeze-thaw cycles, and increased biological activity (particularly Rocks & root penetration). Soils formed during extended wet periods can be released as Landforms sediments once the groundcover is removed during drought conditions, especially by wildfire followed by a rainstorm. Volcanic Rocks & Climate is also a factor in the development of caliche (calcium-carbonate-rich Landforms crusts or soils that form in desert conditions). In North America, caliche is found in arid or semiarid regions of the western states. In many places in the Mojave region Faults & these calium-carbonate-rich crusts form a resistant caprock along stream terraces. Active Tectonics
Pediments & Alluvial Fans
Stream Channel Development
Stream Terraces & Older Surfaces
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Mojave River
Playas
Sand Dunes Caliche-cemented gravels (pale zone topped by a ledge) form the & Dust resistant cap rock of older Pleistocene terrace surfaces along the sides of the modern wash. In the distance, the surface of an older Human quaternary alluvial fan is preserved intact (partly due to a resistant Impacts caliche bed preserved at the surface). The high core of the Selected Providence Mountains in the distance consists mostly of Paleozoic References limestone and dolomite rock formations; these rocks provide calcium carbonate to the alluvium and enhance caliche 3D Geology development. Tour
Index Page
A boulder of the caliche-cemented gravel has been eroded and re- deposited.. It displays rock fragments similar to the modern stream gravels surrounding it.
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Morning sunlight highlights the incised remnants of an older (Pleistocene or Pliocene) alluvial fan along the mountain front of the Granite Mountains. The smoother modern (Holocene) alluvial fan surface stands out in the foreground (in mountain shadows). The incised and eroded condition of this fan suggests different possibilities.
A desert pavement (a surface gravel deposit of tightly packed pebbles, layered just one pebble thick and generally devoid of vegetation) is abundant on Pleistocene-age surfaces, particularly in the mid-fan regions. Pavements such as this occur in areas where the stream flow is restricted to relatively stable channels nearby. Note how little relief exists on this alluvial fan surface on the eastern flank of the Providence Mountains.
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A close-up view of a desert pavement shows that gaps between rock fragments are small or rarely visible (hiding the accumulated dust underneath). Wind and episodic rains keep the surface free of dust, and plants have a difficult time becoming established due to lack of soil. The surface temperature difference between night and day during the summer may range over 100 degrees Fahrenheit. This daily temperature difference may play a role in the formation of these pediment surfaces. Most of the rock fragments shown here are dolomite and limestone.
Continue to the Mojave River page...
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Introduction to the Desert Landforms and Surface Mojave National Processes in the Mojave National Preserve Preserve and Vicinity Physiography
1 Weather By Philip Stoffer Data Open-File Report 2004-1007 General Mojave 2004 Geologic History ABSTRACT: Landscape features in the Mojave National Preserve are a product of ongoing processes involving tectonic Changing forces, weathering, and erosion. Long-term climatic cycles (wet Climates & and dry periods) have left a decipherable record preserved as Ancient landform features and sedimentary deposits. This website provides Lakes and introduction to climate-driven desert processes influencing landscape features including stream channels, alluvial fans, playas Weathering (dry lakebeds), dunes, and mountain landscapes. Bedrock & Erosion characteristics, and the geometry of past and ongoing faulting, fracturing, volcanism, and landscape uplift and subsidence Carbonate influence the character of processes happening at the surface. Rocks & Landforms Use of any traide, firm or product name is for descriptive purposes only and does not constitute endorsement by the U.S. Government. Granitic Rocks & Landforms U.S. GEOLOGICAL SURVEY Volcanic Rocks & U.S. DEPARTMENT OF THE INTERIOR Landforms 1Western Earth Surface Processes Team, Menlo Park, CA Faults & Active Tectonics
Pediments & Alluvial Fans
Stream Channel Development
Stream Terraces & Older
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Surfaces
Mojave River
Playas
Sand Dunes & Dust
Human Impacts
Selected References
3D Geology Tour
Index Page
Continue to the Introducation page.
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Introduction The Mojave River and Associated Lakes to the Mojave National The Mojave River is the largest drainage system in the Mojave Desert. It's modern Preserve extent and capacity is only a fraction compared to its extent during the Last Glacial Maximum. At its peak during this last ice age, the Mojave River drainage basin Physiography extended from the San Bernardino Mountains in the west; it flowed east and north ultimately merging with the Amargosa River before draining into Lake Manley in Weather Death Valley. At this peak period, waters of the Mojave River drainage system Data flowed through, or contributed water to, several great Pleistocene Lakes: Lake Manix (which incorporated modern dry lake basins Afton, Troy, Coyote, Harper, General and Cronese basins), and Lake Mojave (including dry Soda Lake and dry Silver Mojave Lake basins)(see the map on the Changing Climates & Ancient Lakes page). Today Geologic Soda Lake is the current terminal point of the Mojave River (although it has flowed History into Silver Lake in historic times).
Changing This drainage system evolved along with the changing landscape beginning in late Climates & Tertiary time when concurrent tectonic uplift of mountain ranges around the Mojave Ancient region and changes in regional climatic conditions were occurring. The modern Lakes river system began developing as westward-flowing stream drainages were blocked by the uplift of the Transverse Ranges along the greater San Andreas Fault System. Weathering The combination of blocked drainage systems and increased precipitation with the & Erosion onset of cooler or ice age conditions at the close of the Tertiary resulted in the filling of basins with water (and sediments). Progressively through the latest Carbonate Tertiary and into the Quaternary periods, lakes filled and stream overflowed through Rocks & low divides between ranges and flooded adjacent basins. In this manner, the Mojave Landforms River evolved from the spilling over of lakes in the western Mojave Desert region. These large lakes do not exist today. Two large lakes that played perhaps a most Granitic significant role in the development of the landscape in the Mojave National Rocks & Preserve area were Lake Manix and Lake Mojave. Sediments associated with these Landforms ancient lake deposits (and others in the region) record a story of climate change in the region. Volcanic Rocks & Lake Manix was a large inland lake that was located in the Barstow, CA region (dry Landforms Troy Lake and Coyote Lake are remnants of this larger lake basin), and Mojave Lake in the Baker, CA region (dry Silver Lake and Soda Lake are remnants of this Faults & ancient lake basin). The development of these lakes and other lakes in the region Active was progressive with time, with Manix Lake filling first, and Mojave Lake forming Tectonics later when the Lake Manix filled to capacity and spilled westward, ultimately carving Afton Canyon during the last glacial maximum about 18,000 years ago Pediments & (Jefferson, 2003). Alluvial Fans
Stream Channel Development
Stream Terraces & Older Surfaces
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Mojave River
Playas
Sand Dunes & Dust
Human Layers of alluvium exposed in Afton Canyon reveal that changes Impacts in the landscape have occurred over time. The different colored layers of sediments exposed in the cliffs reflect changing Selected environmental conditions and stream source areas as sediments References filled a basin. Afton Canyon formed when a great Pleistocene-age lake that filled the Manix Lake Basin overflowed through a low 3D Geology divide, creating a new path for the Mojave River. Through Tour portions of Afton Canyon the Mojave River is a perennial stream fed in dry periods by groundwater. In the image above the Mojave Index Page River is hidden in the thick tamarask and other brush in the foreground. The intermittent stream draining a small side canyon produced the fan-like sediment apron where it enters the Mojave River floodplain. Note the elevated stream terrace on both sides of the side canyon.
Debate remains whether earlier in the Quaternary the greater Mojave River drainage system (including Lake Manley and the Owens River drainage) filled to overflowing capacity and spilled into the Bristol Lake basin (south of the Mojave National Preserve), or possibly to the Colorado River (Enzel et al., 2003, Cox et al., 2003; Anderson & Wells, 2003). No water from the Mojave River system flows into the Bristol Lake basin at present or in the recent past. And in general, groundwater drainage systems follow patterns in surficial flow, but whether groundwater originating from the Mojave River basin ever makes it to the Colorado River is not resolved.
The synchronicity of lake formation with cooler and wetter climatic conditions in the Mojave region's past has been the target of abundant research from many angles and for many decades. Developing an understanding of climatic cycles (wet to dry) is fundamental to resolving changing landscape conditions (including plant cover, soil development, erosion, alluvial fan processes, playas and lakes, etc.); and understanding the relationships between these different variable elements. For instance, Soda Lake is now essentially a dry lake basin (a playa), of which only temporary flooding occurs on roughly a decade basis. Currently, the Soda Lake basin is fed by groundwater flow and episodic stream discharge from the surrounding mountain ranges and high-flow discharge from the Mojave River. Enzel et al. (2003) suggests that the average annual flow of the lower reaches of the Mojave River would have to be nearly a magnitude larger than the river's average
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current annual flow of 9,500,000 cubic meters. This 10-times volume would be necessary, along with reduced evaporative conditions, to maintain a lake consistent with the last glacial maximum. This means that rainfall amounts would probably need to be several times greater than current regional averages, and seasonal cooling and humidity would need to be significantly greater and last longer to overcompensate for evaporation effects. Currently, evaporative potential in the basin regions exceeds stream and groundwater flow input, and hence, today no lakes exist and desert conditions prevail.
The linkage of climatic changes with surface processes is only partly understood. There is undetermined lag between when cool and wet conditions start and when lakes can form and fill to their capacity. Also, the timing between the start of cool and wet conditions and the when ecological communities adapt and spread across the region may not not be synchronous. The reverse is true for changes from wet to dry conditions. Regional lake deposits show drying occurred about 9,000 years ago as sedimentary records transition from lake deposits, to intermediate marshland conditions, and to dry and desiccated playa conditions. The change from wet to dry conditions had a major impact on the ecology of the Mojave region (the vegetative cover and the animal species the landscape supported, including humans). Plant communities that were probably prevalent throughout the lower landscape regions are now restricted to the highest and wettest mountain areas, and probably many other species existed in the region that were adapted to a completely different seasonal pattern, but do not exist today. Likewise, aquatic or semi-aquatic species (fish, amphibians, turtles, arthropods, etc.) adapted to lake environments are restricted to spring-fed ponds or ephemeral spring fed streams, such as in portions of the Mojave River in Afton Canyon. The distribution of these species across the Mojave region (including in the Colorado River) may require a greater regional drainage system in prehistoric times.
For more information about ecology of the Mojave Desert ecology and climate history, see the USGS Biological Resources Discipline website: http://biology.usgs.gov/s+t/SNT/noframe/gb150.htm.
Continue to the Playas page...
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Introduction to the Playas Mojave National A playa is a dry, vegetation-free, flat area at the lowest part of an undrained desert Preserve basin. It is a location where ephemeral lakes form during wet periods, and is underlain by stratified clay, silt, and sand, and commonly, soluble salts. Playas Physiography occur in intermountain basins throughout the arid southwestern United States. Although playas may appear as featureless plains, they are rich in features and Weather characteristics that can reveal information about climates, past and present. Many Data playas in the Mojave region were the location of lakes and marshes during the last General glacial period. These perennial water bodies completely dried up about 8,000 years Mojave ago. Today they flood only after seasonal storms provide flashflood waters, or in Geologic some cases, springs discharge large quantities of groundwater onto the playa. History Sediments are distributed across the surface of a playa by thin sheets of water that Changing flow down slope (relief on playas may be measurable in only centimeters per mile), Climates & or by sediment entrained in standing water and redistributed by wave action. Most Ancient years playas are dry, or water may only cover the lowest portion of the playa or near Lakes water sources, such as near springs or where ephemeral streams discharge onto the playa surface. Between wet periods the surface of the playa typically completely Weathering dries out and may even become desiccated, forming polygonal cracks and fissures & Erosion as clay-rich sediments dry out. The mud-cracked, desiccated sediments on the playa can be a primary source of dust during windstorms. Many playas in the desert Carbonate southwest display giant polygonal fissures attributed to the drying out of sediments Rocks & at depth; these fissures are attributed to both the ongoing climatic drying of the Landforms region and to extraction of groundwater (Neal & Motts, 1967). Playa surfaces are quite dynamic environments with surface channels, playa margins, sedimentary Granitic materials, and biota changing with each flooding event. Rocks & Landforms On playas where the groundwater table is at or near the surface, soluble salts will precipitate, forming ephemeral crusts that may or may not survive subsequent Volcanic wetting episodes. The high salt and clay content of playa surface mud, and the dry Rocks & and hot conditions that prevail most of the year, prevent plants from becoming Landforms established. However, the surface of a playa may not be completely homogeneous. Sand may accumulate in channels, fill in desiccation fissures, or accumulate around Faults & spring mounds; these areas may allow plant communities to become established. Active Tectonics Playas typically form in closed basins or where drainages may be blocked by faulting, lava flows, or buildup of alluvial fans. Their location within a basin may Pediments & provide evidence whether the basin is tectonically active. For instance, the playa in Alluvial Fans southern Death Valley is located immediately adjacent to rising Black Mountains (to the east) where the valley is rapidly sinking; whereas on the opposite side of the Stream playa huge alluvial fans drain from the Panamint Mountains (to the west). The Channel assymetry of the valley, mountains, and playa are all dictated by active faults. In Development addition, coalescing alluvial fans may create catchments that result in the formation of small playas. Stream Terraces Although there are numerous playas in the region, the Mojave National preserve & Older only has two significant playas, much of the dry Soda Lake and part of Ivanpah dry Surfaces lake (see the aerial photograph on the Physiography page). During the Last Glacial Maximum the low divide between Soda Lake and Silver Lake to the north was
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Mojave flooded (a human modified channel now exists between the two lake beds), and an River ancient beach ridge locally occurs 40 feet above the north end of the Silver Lake playa. At this elevation, the divide between Soda Lake and Cronese basin (with its Playas two playas, West Cronese Lake and East Cronese Lake) would have been flooded. This expanded lake system is known as ancient Lake Mojave. The surface of Silver Sand Dunes Lake playa is more than 10 feet lower than the low end of Soda Lake playa (near & Dust Baker). As much as 10 feet of water has been reported on Silver Lake playa at Human irregular intervals (Thompson, 1929). Impacts Soda Lake is the largest playa in the park, being about 60 square miles. The two Selected images below taken in the vicinity of one of several springs along the west side References (near Zzyzx) illustrate the transition from wet to dry conditions on the playa. The existence of the spring demonstrates the groundwater table is at or near the surface 3D Geology along the west side of the playa (an attempt to walk on the wet playa surface will Tour result in a very muddy experience). During dry periods, alkali salts, primarily sodium carbonate and sodium bicarbonate, form a frothy-white coating on the Index Page surface throughout the south and southwest portion of the playa. Salt crusts do not form at the north end of the playa (or on Silver Lake) probably because the groundwater table is more than 20 feet below the surface, and increase in depth northward into the Silver Lake valley (Thompson, 1929). The salts accumulate through capillary rise of salty groundwater and evaporation. These salts return to the groundwater when it rains.
These salts contribute much to the wind-blown dust and haze in the Mojave region late in the summer and fall. Sediment provided by the discharge of the Mojave River into the Soda Lake basin is the source of much of the clay, silt, and sand in the playa sediments. The sand from the Mojave River is the primary source of eolian sand for Kelso Dunes and Devils Playground.
Winter storm precipitation results in increased water discharge onto Soda Lake from one of several springs near Zzyzx, CA (photo by Dave Bedford, February, 2001).
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This view of the springs area near Zzyzx shows that by late spring the flaky soda crust deposts have redeveloped on the surface of Soda Dry Lake (photo taken in May, 2003).
Continue to the Sand Dunes & Dust page...
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Introduction Sand Dunes & Dust to the Mojave National Processes involving sand and dust transport play an important roll in shaping the Preserve landscape and the ecosystem of the Mojave region. Barren rock, alluvium, and dry lake beds are all sources of dust and sand. Typically most dust (clay and silt) Physiography becomes suspended in the wind and is carried away from the region by prevailing winds, particularly during wind storms when high dust concentrations in the air can Weather create near "white-out" conditions. In contrast, wind moves sand along the surface Data as a saltating bedload. The moving sand will stall and accumulate as dunes where the wind rises over a barrier (such as a mountain range). However, for dunes to General persist, a sand source area must provide a sufficient flux of new sand, otherwise Mojave both wind and running water will remove sand faster than it can accumulate, and Geologic therefore, prevent dune development or cause existing dunes to diminish or even History vanish.
Changing The Kelso Dunes and Devils Playground is a large area of eolian (wind blown) sand Climates & deposits within the Mojave National Preserve; the dune field is also the largest in Ancient the Mojave Desert region. The dune field contains dunes (both actively- Lakes forming/migrating dunes and plant-stabilized dunes), sand sheets (sandy flats areas transitional between the source areas and the dunes), and sand ramps (sand build- Weathering ups on the flanks of the mountains). The dune field is are located in the southeastern & Erosion end of the greater Soda Lake-Kelso basin where the Granite Mountains and southern Providence Mountains form a barrier to prevailing winds. Wind entraining Carbonate a flux of sand derived mostly from the Mojave River area at the western end of the Rocks & basin is deposited near the rising mountain front of the Granite and Providence Landforms Mountains, causing the coarser fractions to accumulate. Granitic Rocks & Landforms
Volcanic Rocks & Landforms
Faults & Active Tectonics
Pediments & Kelso Dunes in morning light. The Granite Mountains form the dark Alluvial Fans ridge to the left. Stream Channel Development
Stream Terraces & Older Surfaces
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Mojave River
Playas The star dune (highest dune) in the Kelso Dunes rises about 300 feet (100 m) above lower, plant-stabilized dunes along the Sand Dunes southern margin of the dune field. & Dust The changing climate of the Quaternary (wet to dry, and reverse) has influenced the Human formation, stabilization, destruction, and re-activation of dune field systems through Impacts time. The Kelso Dunes probably looked much different during the wet periods of the Quaternary than they do today. In fact, field evidence suggests they may have Selected been mostly or entirely stabilized by plant cover in the past, much as the great dune References field of the Sand Hills of Nebraska are stabilized by vegetation today.
3D Geology Lake sediments constitute one of the major sources for eolian sediment, along with Tour sediments derived from lower (distal) alluvial fans and ephemeral washes (such as Mojave River for the Kelso Dunes field). Investigations have demonstrated that at Index Page least two major pulses of dune emplacement occurred between 35,000 to 25,000 and 15,000 to 10,000 years before present, and a period of active dune reworking and construction has been ongoing for most of the past 4,000 years (Tchakerian and Lancaster, 2002; Lancaster and Tchakerian, 2003). These are times of dramatic increase in sediment supply from drying lakes and river input.
The size, character, and extent of dune fields depend on many variables that determine the supply and mobility of eolian sediments. Factors include source materials, wind direction and magnitude, precipitation patterns, and landscape (geospatial) configurations relating to sediment supply, migration paths, and depositional setting. During wet periods, vegetation cover stabilizes dunes, leads to soil formation, and curtails eolian sediment supply from source regions (playas, washes, fans, etc.). Conversely, during arid periods these source regions are re- activated. In addition, the extent of ancient Lake Mojave during highstands in lake levels in the Quaternary may have isolated Kelso Dunes from their sediment source area. However, the linkage between climate and dune re-activation is not clearly resolved. When dry periods persist, the supply of sediment provided by streams may cease, and the readily wind-transportable material may diminish. As a result, sand dunes may erode away due to lack of the supply of new sand, and desert pavements may form. The probable most effective climate for sand dune field formation is a balance of episodic, intense storms (to generate and move sediments to eolian source areas) with intervening windy, long, hot, dry periods (to hinder soil development and plant growth).
For every bucket of sand that migrates into the Kelso Dunes, an undetermined volume of dust is generated that disappears into the wind. Dust storms in the Mojave region can be quite intense, and a hazard when dust concentrations are high enough to cause white-out conditions. Windblown dust can be harmful to people breathing it. Dust may contain toxic compounds and it can carry pathogens such as the virus that causes Valley Fever; it also carries away valuable topsoil. On the otherhand, http://pubs.usgs.gov/of/2004/1007/dunes.html[2/21/2014 3:47:15 PM] Our Dynamic Desert
dust that settles into stony soils of the desert provides improved retention of moisture and adds nutrients. Thus, dust can be both beneficial and destructive.
For more information about climate change and dust in the Mojave region and Desert Southwest see the USGS website on Impacts of Climate Change and Land Use on the Southwest.
Continue to the Human Impacts page...
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Introduction Human Impacts on the Mojave National Preserve to the Mojave Area National Preserve Evidence of human history in the Mojave region extends back to when perennial lakes existed in the region at the close of the Pleistocene, nearly 10,000 years ago, Physiography or possibly earlier. Although the Mojave Desert has a rich archeological record, the numbers of humans were probably minimal compared with modern populations. Weather Evidence of early human inhabitation has been found along the shorelines of pluvial Data lakes. The people had to adapt to the changing climate along with the fauna and flora. It is likely that both early Holocene climate change and human predation were General responsible for the disappearance of large mammal populations from the western Mojave United States (including the dire wolf, giant short-faced bear, saber-toothed cat, and Geologic California lion). Of 67 genera of North American mammals known to have become History extinct during the Pleistocene, about 35 vanished between 13,000 and 8,000 years Changing before present; in addition 10 genera of California birds vanished in the same period Climates & (Moratto, 1984). Ancient Compared with modern populations, small numbers of Native Americans utilized Lakes the Mojave region at the time of European contact in the 1600's. The tribes along Weathering the Colorador River corridor of the eastern Mojave included the Mojave, & Erosion Halchidmoma, and Kohuana (or Chemehuevi or Southern Paiute); in the more western part of the Mojave National Preserve region were Chemehuevi (or Southern Carbonate Paiute) and Desert Cahuilla tribes (Heizer and Whipple, 1971). The Mojave was the Rocks & largest tribe and was found distributed throughout the region from the Colorado Landforms River to the San Bernardino Mountains. Most of the Mojave's Native American population vanished from imported diseases, subjugation, and hostilities prior to the Granitic 1860's. Rocks & Landforms Earliest European migration into the Mojave region began with the Spanish, mostly along the western side of the Mojave Desert in the early 1700's, and steadily Volcanic increased to a massive migration during the 1849 Gold Rush era. Two early travel Rocks & routes crossed portions of the Mojave National Preserve: the Old Spanish Trail and Landforms the Mojave Road (which shared some of the same route). Both routes probably utilized older Indian trails that interconnected perennial water sources. Faults & Active Between 1598 and 1821 as Spanish exploration, migration, and trade routes Tectonics converged on the Mojave region from population centers in New Mexico, Sonora, and southern California. By 1830, a system of interconnecting trails became know Pediments & as the Old Spanish Trail. The Old Spanish Trial begins north out of Santa Fe, New Alluvial Fans Mexico and crosses the West north of the Colorado River along various routes with a terminal destination of Los Angeles, California. Stream Channel Traces of the Old Spanish Trail (and an alternative route) come into the Mojave Development National Preserve area from the north and east and merge to the west. Various routes may have converged at perrenial water sources at the springs along the shore Stream of Soda Lake (near Zzyzx), but the two main routes historically intersected along the Terraces Mojave River near Yermo, west of Afton Canyon. The northern route came south & Older from the Pahrump Valley, through Tecopa, and south through historic Valgean in Surfaces the Silver Lake valley into what is now the Baker area (along Highway 127). The alternative southern route came in from the east via the Colorado River and crossed
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Mojave through the Preserve, basically following what later became the Government Road. River Petroglyph inscriptions of early travelers are preserved at Piute Springs (in the Preserve) and include notable historic names: Garcés, Smith, Whipple, and Beale. Playas Beale directed a government land survey in 1853. One historic inscription reads "Stuart, 4th Inft. May 16, 1851" [though the last digit may be another number]. Sand Dunes Another notable expedition along the trail included Kit Carson and Lieutenant & Dust George D. Brewerton in 1848.(NPS, 1998 and NPS, 2001).
Human During the Mexican War, 1846-1848, the Americans' Army of the West conquered Impacts New Mexico, then blazed new, southern variants of the route to California, hastening the end of the Old Spanish Trail. The Old Spanish Trail was utilized Selected during the California Gold Rush of 1849, and then by traffic between Mormon References settlements and commerce between Salt Lake City and Los Angeles. Traffic 3D Geology diminished along the Old Spanish Trail as alternative routes developed. Two key Tour factor leading to its decline included the abandonment of a Mormon settlement in San Bernardino in 1857 and completion of the Transcontinental Railroad in 1869. Index Page The Mojave Road (or Old Government Road) began in the east at Fort Mojave (now long gone) on the banks of the Colorado River and extended west to historic Camp Cady (about 20 miles east of Barstow). Along the route travelers typically camped near several perenial water sources including Fort Piute, Hole-In-The-Wall, and Marl Spring, and springs along Soda Lake shore (near Zzyzx). During the period of 1860-1880 the road primarily served travelers heading west to the growing coastal cities.
Map showing the trace of the historic "Mojave Road" with the location of water sources along the route. Fort Piute was a small desert post located near Piute Springs in the foothills of the Piute Mountain range, about 25 miles west of Fort Mojave.
Modern human impacts in the Mojave National Preserve region began with small mining and ranching operations in the 1880s. The Arrowhead gold mining district was established in 1882 with the location of the Hidden Hill mine in the southwest end of the Providence Mountains; large-scale gold mining took place with the Big http://pubs.usgs.gov/of/2004/1007/humans.html[2/21/2014 3:47:25 PM] Our Dynamic Desert
Horn mine from 1918 until the Great Depression of the 1930's (Clark, 1930). Many claims and patented mines became established in the region in this era of "boom and bust" but most mines were not profitable but for a short time. Minerals mined throughout the Mojave National Preserve region included ores of gold, silver, lead, copper, iron, molybdenum, lead, tungsten, and zinc. The town of Baker began as a watering stop for the Borax mule trains bound from Death Valley. Larger scale impacts didn't begin until railroad lines were laid to service mines in the region.
Map showing the location of selected historic mines and mining prospects in the Mojave National Preserve area. For detailed mineral resource summary for the Mojave National Preserve see Theodore and others, (2003). Numbered mines and prospects sites on this map are described by Hewett (1956). Mineral resources in the Providence Mountains are described by Miller and others (1985) and Goldfarb and others (1988). Mine and information around the south and west side of the preserve are not included on this map. For a larger version of this map, click here.
Railroad lines include the current rail that passes Kelso Depot. Historic spur routes included a route to Goffs via Ivanpah and Lanfair Valley, a spur to Searchlight, and a route connection Ludlow to Death Valley (via Soda and Silver Lake valleys). By the mid 1920's automobiles became the primary mode of transportation across the region.
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The first rail lines through the Mojave Desert were completed in 1906; the Kelso Depot was built in 1924 by the Union Pacific Railroad to serve as a transfer point and water station. In the 1940s nearly 2,000 people lived in the Kelso vicinity, most were employees or families associated with nearby mining operations. With mine closures after WWII, and as diesel locomotives replaced steam engines, Kelso Depot was no longer needed to water the steam locomotives. By the 1950s, the once thriving town of Kelso nearly vanished. Kelso Depost is currently being restored to serve as a National Park Service visitor center.
The World War II era was perhaps the time of greatest human impact on the region; military activities, mining, and road building being the most important impacts. "General Patton's Army" used parts of Lanfair, Fenner, and Piute valleys as a training grounds and camps before shipping troops off to conduct desert warfare in Africa. The Vulcan Mine, the largest mining operation now in the preserve, supplied iron for the war effort. Road building associated with mining operations, railroads, and utilities carrying electricity, gas, and water to the greater Los Angeles region produce long-lasting traces across the landscape. After 50 years, many of the old traces of tank tracks are gradually vanishing, particularly on active washes and alluvial fan areas, but in some areas, such as flats that rarely flood, many of these traces are still clearly visible.
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The Vulcan Mine opened in 1942 to provide iron needed for World War II. The mine is located nine miles south of Kelso. During the war trains carried more than 2,500 tons of ore a day to the Kaiser Steel Mill in Fontana, California. Kaiser closed the Vulcan Mine shortly after the war because the ore contained too much sulfur.
The "modern era" brought perhaps the greatest changes to the Mojave Region, first perhaps with negative impacts, but ultimately with the hopeful positive outcome of establishment of the Mojave National Preserve.
With funds from Congress in 1926, Route 66 was designated for the Chicago-to-Los Angeles route. By 1930, the route had become one of the main east-to-west transportation corridors across the United States with automobiles and trucks supplanting railroads as the primary mode of transporting people and materials crosscountry. Route 66 crosses the Mojave region between Needles and Barstow, including the towns of Goffs and Ludlow (just south of Interstate 40 along the southern boarder of the Mojave National Preserve).
The passage of the Federal Aid Highway Act of 1956 provided funds to develop of the national interstate and defense highway system, and by 1970, nearly all segments of the original Route 66 were replaced by a modern four-lane highway (I- 40 in California). I-15 was built to connect the growing city of Las Vegas with the San Diego and Los Angeles metropolitan regions. This interstate replaced older highways between Barstow and the Nevada state line: US 91 and US 466.
The growing population of the west brought increasing pressure on the development of the Mojave Desert. Additional utility lines (electricity, gas, and water) and their service roads were developed. Whereas the settlements within what is now the Preserve continued to dimish with the decline in mining, ranching, and railroads, the building of highways encouraged an influx of tourists with a wide mix of interests in the Mojave region. Off-highway vehicle enthusiasts discovered the Mojave Desert, and perhaps the worst period of environmental degredation of the Mojave Desert landscape began. The growing environmental conscience starting perhaps in the late 1960s lead to the establishment of the Mojave National Preserve that was created in October 1994 when Congress passed the California Desert Protection Act.
Additional human impacts in the region include the ongoing extraction of water and associated lowering of groundwater tables (springs dry up), groundwater contamination (particularly from mining wastes), the introduction of invasive species and vanishing habitats, (redbrome grass is of perhaps of primary concern for habitat loss, and is a fire hazard), ongoing grazing, and the influx of air pollution from the metropolitan areas. In addition, the ongoing natural progression of climate change may produce significant impacts over the long term. Only time will show how the whole ecosystem, or parts of it, will respond to the combined effects of climate change and human interactions.
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Cottonwoods displaying autumn colors stand out in contrast to the evergreen Joshua tree forest in the high desert near Kessler Spring in the Mojave National Preserve.
Continue to the Selected References page...
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Introduction Selected References On the Geology and Surface to the Mojave Processes of the Mojave National Preserve Region National Preserve A cursory search on the GeoRef literature database in July, 2003 yielded over 3,000 citations (including over 150 websites); most of these references are technical Physiography reports or conference meeting abstracts. The reference list below includes sources used in this report, and selected references that the writer found most useful in Weather gathering background information for this website. Many of the recent articles cited Data below (particularly from GSA Special Paper 368) have rich reference lists that point to primary reference sources and methodologies used in Quaternary dating methods General and field data collection. Mojave Geologic ------History Anderson, D.E. and Wells, S.G., 2003, Latest Pleistocene lake highstands in Death Changing Valley, California: In Paleoenvironments and paleohydrology of the Mojave and Climates & southern Great Basin deserts: Enzel, Y., Wells, S.G., and Lancaster, N., (eds.): Ancient Geological Society of America Special Paper 368, p. 115-128. Lakes Bishop, C.C., 1963, Geologic map of California: Needles sheet: California Division Weathering of Mines and Geology, scale 1:250000. & Erosion Bortugno, E.J. and Spittler, T.E., 1986, Geologic map of the San Bernardino Carbonate quadrangle, California: California Division of Mines and Geology, Regional Rocks & Geologic Map 3A, scale 1:250000. Landforms Blackwelder, E., 1954, Pleistocene lakes and drainage in the Mojave region, Granitic southern California: California Department of Natural Resources Bulletin 170, Rocks & Chapter 5, Part D, p. 35-40. Landforms Brussard, P.F., Dobkin, D.S., 2003, Great Basin--Mojave Desert Region: U.S. Volcanic Geological Survey, Biological Resources Division website: Rocks &
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Mojave Dohrenwend, J.C., Wells, S.G., Turrin, B.D., and McFadden, L.D., 1986, River Degradation of Quaternary cinder cones in the Cima volcanic field, Mojave Desert, Playas California: Geological Society of America Bulletin, v. 97, no.4, p. 421-427.
Sand Dunes Enzel, Y., Wells, S.G., and Lancaster, N., 2003, Late Pleistocene lakes along the & Dust Mojave River, southeast California: In Paleoenvironments and paleohydrology of the Mojave and southern Great Basin deserts: Enzel, Y., Wells, S.G., and Human Lancaster, N., (eds.): Geological Society of America Special Paper 368, p. 61-78. Impacts Enzel, Y., Wells, S.G., and Lancaster, N., 2003, Paleoenvironments and Selected paleohydrology of the Mojave and southern Great Basin deserts: Geological Society References of America Special Paper 368, 250 p.
3D Geology Goldfarb, R.J., Miller, D.M., Simpson, R.W., and Hoover, D.B., 1988, Mineral Tour Resources of the Providence Mountains Wilderness Study Area, San Bernardino County, California: U.S. Geological Survey Bulletin 1712D, 70 p., map scale Index Page 1:62,500. Harvey, A.M. and Wells, S.G., 2003, Late Quaternary variations in alluvial fan sedimentologic and geomorphic processes, Soda Lake basin, eastern Mojave Desert, California: In Paleoenvironments and paleohydrology of the Mojave and southern Great Basin deserts: Enzel, Y., Wells, S.G., and Lancaster, N., (eds.): Geological Society of America Special Paper 368, p. 207-230.
Heizer, R.F. and Whipple, M.A., 1971, The California Indians, 2nd Edition: Berkeley, Ca: University of California Press.
Hewitt, D.F., 1956, Geology and mineral resources of the Ivanpah quadrangle, California and Nevada: U.S. Geological Survey Professional Paper 275, 172 p.
Jefferson, G.T., 2003, Stratigraphy and paleontology of the middle to late Pleistocene Manix Formation, and paleoenvironments of the central Mojave River, southern California: In Paleoenvironments and paleohydrology of the Mojave and southern Great Basin deserts: Enzel, Y., Wells, S.G., and Lancaster, N., (eds.): Geological Society of America Special Paper 368, p.43-60.
Jennings, C.W., 1961, Geologic map of California: Kingman sheet: California Division of Mines and Geology, scale 1:250000.
Jennings, C.W., Burnett, J.L., and Troxel, B.W., 1962, Geologic map of California: Trona sheet: California Division of Mines and Geology, scale 1:250000.
Lancaster, N. and Tchakerian, V.P., 2003, Late Quaternary eolian dynamics, Mojave Desert, California: In Paleoenvironments and paleohydrology of the Mojave and southern Great Basin deserts: Enzel, Y., Wells, S.G., and Lancaster, N., (eds.): Geological Society of America Special Paper 368, p. 231-249.
McDonald, E.V., McFadden, L.D., and Wells, S.G., 2003, Regional response of alluvial fans to the Pleistocene-Holocene climatic transition, Mojave Desert, California: In Paleoenvironments and paleohydrology of the Mojave and southern Great Basin deserts: Enzel, Y., Wells, S.G., and Lancaster, N., (eds.): Geological Society of America Special Paper 368, p. 189-205.
Meek, N., 1989, Geomorphic and hydrologic implications of the rapid incision of
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Afton Canyon, Mojave Desert: Geology, v. 17, p. 7-10.
Miller, D.M., Glick, L.L., Goldfarb, R.J., Simpson, R.W., Hoover, D. B., Detra, D.E., Dohwenwend, J.C., and Munts, S.R., 1985, Mineral resource potential map of the South Providence Mountains Wilderness Study Area, San Bernardino County, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-1780-A, 29 p.
Miller, D.M., and Wooden, J.L., 1993, Geologic map of the New York Mountains area, California and Nevada: U.S. Geological Survey Open-File Report 91-198, 10 p., scale 1:50,000.
Miller, D.M., Miller, R.J., Nielson, J.E., Wilshire, H.G., Howard, K.A., Stone, P. 1991. Preliminary geologic map of the East Mojave National Scenic Area: U.S. Geological Survey Open-File Report 91-435, scale 1:100,000.
Moratto, M.J., 1984, California Archaeology: Orlando: Academic Press, Inc.
National Park Service, 2001. National Historic Trail Feasibility Study and Environmental Assessment, Old Spanish Trail: U.S. Dept. of Interior, National Park Service, 151 p.
National Park Service, 1998, The Old Spanish Trail: National Historical Trail Feasibility Study Newsletter 1 (February 1998), 3 p.
Neal, J.T and Motts, 1967, Recent geomorphic changes in playas of the western United States: Journal of Geology, v. 75, no. 5, p. 511-525. (Reprinted in Playas and Dried Lakes, Neal, J.T., (ed.), (Benchmark Papers in Geology, v. 20): Dowden, Hutchinson & Ross, 1974.)
Reynolds, R.E., (ed.), 1994, Off Limits in the Mojave Desert: Field Trip Guidebook and Volume For the 1994 Mojave Desert Quaternary Research Center Field Trip to Fort Irwin and Surrounding Areas: San Bernardino County Museum Special Publication 94-1, 100 p.
Reynolds, R.E., (compiler), 1985, Cajon Pass to Manix Lake: Geologic Investigations along Interstate 15: San Bernardino County Museum, 191 p.
Reynolds, R.E. and Reynolds, J., (eds.), 1995, Ancient Surfaces of the East Mojave Desert: San Bernardino County Museum Association Quarterly, v. 42, no. 3, 160 p.
Reynolds, R..E., Wells, S.G., and Brady, R.H., III, (compilers), 1990, At the End of the Mojave: Quaternary Studies in the Eastern Mojave Desert: San Bernardino County Museum Association Special Publication, 134 p.
Sharp, R.P., 1954, The nature of Cima Dome: In Jahns, R.H. (ed.), Geology of southern California, [Part 8], v. 68, no. 3, p. 49-52.
Sharp, R.P., 1982, Kelso Dunes: In Geologic excursions in the California desert, Cooper, J.D. (ed.), Boulder, CO: Geological Society of America, p. 83-87
Tchakerian, V.P. and Lancaster, N., 2002, Late Quaternary arid/humid cycles in the Mojave Desert and western Great Basin of North America: Quaternary Science Reviews, v. 21, no. 7, p. 799-810.
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Theodore, T.G., (ed.), 2003, Geology and mineral resources of the East Mojave National Scenic Area: U.S. Geological Survey Bulletin 2160, 279 p.; http://geopubs.wr.usgs.gov/bulletin/b2160/.
Thompson, D.G., 1929, The Mojave Desert Region, California: A Geographic, Geologic, and Hydrologic Reconnaissance: U.S. Geological Survey Water-Supply Paper 578, p. 559-568. (Excerpted version reprinted under the title "Soda Lake and Silver Lake" in Playas and Dried Lakes, Neal, J.T., (ed.), (Benchmark Papers in Geology, v. 20): Dowden, Hutchinson & Ross, 1974.)
Thompson, R.S., 1998, A Strategy for Assessing Potential Future Changes in Climate, Hydrology, and Vegetation in the Western United States: U.S. Geological Survey Circular 1153, 20 p.
U.S. Geological Survey, 1991, Evaluation of Metallic Mineral Resources and Their Geologic Controls in the East Mojave National Scenic Area, San Bernardino County, California: U.S. Geological Survey Open-File Report 91-427, 278 p., (with six map plates).
Wells, S.G., Brown, W.J., Enzel, Y., Anderson, R.Y., and McFadden, L.D., 2003, Late Quaternary geology and paleohydrology of pluvial Lake Mojave, southern California: In Paleoenvironments and paleohydrology of the Mojave and southern Great Basin deserts: Enzel, Y., Wells, S.G., and Lancaster, N., (eds.): Geological Society of America Special Paper 368, p.79-114.
Wells, S.G., Anderson, R.Y., McFadden, L.D., Brown, W.J., Enzel, Y., and Miossec, J.L., 1989, Late Quaternary paleohydrology of the Eastern Mojave River drainage, southern California: quantitative assessment of the Late Quaternary hydrologic cycle in large arid watersheds:
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