13.1: Physiographic Features of the Mojave and Colorado Desert Provinces
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Location and Geomorphology of California's Desert Geomorphic Provinces
Together, the Mojave and Colorado Desert Provinces form a triangular wedge of desert terrain in southeast California, which shares many of the general physiographic and geologic features found to the north in the Basin and Range Province. Two distinct deserts underlie this region: the Mojave Desert and the Colorado Desert. Both regions exhibit basin and range style topography, although it is more muted than that of the Basin and Range Province. While the geology of these two regions records a long portion of Earth’s history, climatic changes during the last million years are largely responsible for most landscape features present today. For that reason, these two deserts make an excellent study ground for desert processes.
The Mojave Desert is bounded by the Garlock fault to the north (Figure \(\PageIndex{1}\)). Lying in the rain shadow of the southern Sierra Nevada mountains and the Transverse Ranges, the overall range in elevation of this high desert region is between 610-1220 meters (2000-4000 ft) above sea level. The I-15 highway travels northeast across this region.
The Colorado Desert lies to the south of the Mojave and extends to the southeastern border of California. It is part of the larger Sonoran Desert region, which extends into northern Mexico and western Arizona. The average elevation of this low desert region is approximately 305 m (1000 ft) above sea level; the lowest point is -82m (-269 ft) below sea level at the Salton Sea and the highest peaks are no more than 914 m (3000 ft) above sea level. Because of its overall low average elevation, it is sometimes referred to as the "Salton Trough". Although this region is arid, lying in the rain shadow of the Peninsular Ranges to the west, large portions are heavily irrigated for agriculture (the Imperial and Coachella Valleys that are north and south respectively of the Salton Sea).
Important and well known geographical landmarks in these regions include Red Rocks State Park, the Kelso Dunes, Mitchell Caverns, the Mojave National Monument, Joshua Tree National Park, Anza-Borrego Desert State Park, Sonny Bono Salton Sea National Wildlife Refuge, and the Coachella Valley.
Mountains and Valleys
The simplified geological relationships in this region can be described as North-South trending exposures of uplifted basement rocks in the footwalls of Northwest-Southeast trending normal faults. Rocks exposed in these ranges include Late Proterozoic igneous and metamorphic rocks, Paleozoic sedimentary units, and Mesozoic igneous and metamorphic rocks (Figure \(\PageIndex{2}\)). Ranges containing these older units are separated by basins filled with unlithified or weakly lithified sedimentary deposits that include alluvial fans and extensive seasonal (dry) lake beds, as well as sand dune fields and features, and the tracks of ephemeral river systems. Throughout this province, outcrops of younger (Late Cenozoic) volcanic rocks (cones, domes, flows, and tuff) overlap and are cut by the normal faults.
The southern portion of the Colorado Desert Province marks a transition from continental rift-related fault features to those associated with seafloor spreading in the northern Gulf of California to the south. The geologic features of this region are discussed in more detail in the following sections.
The Mojave and Colorado Desert regions that lie within California were included into the World Network of Biosphere Reserves by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) in 1984. Biosphere reserves are learning areas for sustainable development under diverse ecological, social and economic contexts, touching the lives of more than 250 million people. There are currently 727 biosphere reserves in 131 countries, including 22 transboundary sites.
Biosphere Reserves involve local communities and all interested stakeholders in planning and management. They integrate three main "functions":
- Conservation of biodiversity and cultural diversity
- Economic development that is socio-culturally and environmentally sustainable
- Logistic support, underpinning development through research, monitoring, education and training
These three functions are pursued through the Biosphere Reserves' three main zones:
- Core Areas comprise a strictly protected zone that contributes to the conservation of landscapes, ecosystems, species and genetic variation
- Buffer Zones surround or adjoin the core area(s), and are used for activities compatible with sound ecological practices that can reinforce scientific research, monitoring, training and education.
- Transition Area where communities foster socio-culturally and ecologically sustainable economic and human activities.
The Mojave and Colorado Deserts Biosphere Reserve includes a cluster of 3 core areas (Death Valley National Park, Joshua Tree National Park, and Anza-Borrego Desert State Park and Santa Rosa and San Jacinto National Monument) and a substantial percentage of the northern Mojave and Colorado Deserts surrounding these areas, the Mojave and Colorado Deserts Biosphere Reserve is one of only 46 ecosystems in the United States with this special designation.
References
- Mojave Desert Geomorphic Province. (n.d.). Digital-Desert. Retrieved September 4, 2023, from http://digital-desert.com / geomorphic-provinces/mojave-desert.html
- What are Biosphere Reserves? (n.d.). UNESCO. Retrieved August 31, 2023, from https://en.unesco.org/biosphere/about
- Wick, B., & Hansen, K. (2016, March 12). A Monumental Addition in California. NASA Earth Observatory. Retrieved August 31, 2023, from https://earthobservatory.nasa.gov/images/87668/a-monumental-addition-in-california