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Mojave Desert
Mojave Desert
The Mojave encompasses approximately 25,000 square miles, crossing four state lines (California, Arizona, Nevada, and Utah). The desert is surrounded by mountains but, on average, has few changes in elevation (typically between 3,000 and 6,000 feet). (3) An exception to that is Death Valley which contains both the lowest point in North America (Badwater Basin, -282 feet) and a mountain (Telescope Peak, 11,049 feet). (3) The desert also experiences intense daily and seasonal temperature variability. One of the few places in the American southwest that reflects the four seasons, summer temperatures in the Mojave can reach 120 F and winter temperatures can dip below freezing! (3)
Joshua Tree in winter, Flickr
Joshua Tree at dusk, Wikimedia Commons
As the name would suggest, the Mojave Desert is in a state of constant water shortage. Streams are uncommon across the interior of the desert; however, three rivers within and surrounding the area allow for the desert’s survival: the Mojave River, the Amargosa River, and the Colorado River. The Mojave receives little precipitation (between 65 and 190 mm annually) and subsequently it has many dry lakes. (2)
The geology of the Mojave varies depending on where you visit. Quartz and feldspar particles make up the Kelso Sand Dunes. (5) Volcanic activity from the Tertiary Period (65.5 - 2 million years ago) led to metamorphic rock formations in the eastern Mojave and borate mineral deposits found at Artist’s Palette, Death Valley. (1) Evaporated ancient lakes provided the basis for salt flats found at places like Badwater Basin. However, a majority of the Mojave Desert’s soil consists of coarse-grained, stony alluvial fan materials. (4)
Colorado Desert
Colorado Desert
The Colorado Desert is located in Southeastern California. This desert is only a small portion of the much larger Sonoran Desert that extends to Arizona all the way down to Baja California and a portion of Mexico.
The Sonoran Desert has a rich history of geological formation that dates all the way back 20 million to 40 million years ago (6). Volcanic activity coupled with tectonic activity during that time led to the formation of large basins and mountain ranges (6). The height of some of these mountain peaks can range between 3,000 and 10,000 feet (6). However, as some areas rose, other areas sank. This created trough-like systems such as the Salton trough which is located 275 feet below sea level (7). The rain shadow effect, where mountains block the passage of rain-producing weather systems to the leeward side of the mountain and create a 'shadow' of dryness, produced by these mountain ranges led to the formation of the Colorado desert (8).
Justin Kolenc, Picture of a small portion of the Colorado Desert
John Enfield. The lines are showing the clear distinction between the soil types going from grainy to coarse then to compact.
What makes the Colorado desert unique is the fact that it experiences a higher rainfall than California's other deserts with 6.9 inches of annual rainfall (9). The soils in the Colorado desert are comprised of coarse grain sandy soils which in turn lead to high porosity. Water will travel through the soil layers fairly quickly down and very little rain is captured before it reaches the groundwater (10). The soil is often frequently alkaline, restricting the number of species which can grow in the system without particular adaptations (10).
Besides annual rainfall, there are two main sources of water in the Colorado desert. The first is the Colorado river and the second is the Salton Sea. The Colorado river is often referred to as the lifeline of the Southwest, as it carries water from Colorado to the Gulf of California. In the distant past, the Colorado desert would have flooded into Lake Cahuilla; however, due to channelizing of the Colorado river lead to the drying of this lake within 50-60 years (9 & 11). There is evidence of this old lake in the exposed sides of mountains. During heavy rainfall, some of the Colorado river can still overflow.
The second source of water in this desert is the Salton Sea. This sea was unintentionally formed in 1905 when a canal used to mitigate Colorado river flooding burst. By the time the break was contained, the Salton basin had become the Salton sea. The Salton sea is now maintained through agricultural runoff from the Coachella and Imperial Valleys (11).
Rennett Stowe , A fire in a desert
Fires in the Colorado desert tend to be quite uncommon; however, if one does occur it can dramatically shift the plant ecology. The Colorado desert tends to be dominated by Creosote-bush scrub and is not fire tolerant. If more than 10% of the above ground biomass burns its chance of survival is drastically decreased (12). With increased fire rates, a type conversion will take place, shifting the community from being Creosote bush dominated to invasive grass dominated.
The Colorado desert is very prone to earthquakes due its unique location on the San Andreas Fault (between the Pacific tectonic plate and the North American Tectonic plate). The San Andreas fault runs right through a portion of the Colorado desert and through the Salton Sea.
Great Basin Desert
Great Basin Desert
Geographic map of the Great Basin region, image from Wikimedia Commons.
The Great Basin desert is located within the Western United States and spans a large swathe of land, encompassing four different states. These include parts of eastern California, western Utah, Idaho, and a large portion of the state of Nevada. The Great Basin desert is known as a “cold desert” which means that precipitation comes as snow rather than rain. It is considered to be the only cold desert of all the major deserts in the United States. It’s climate depends on the season: during the summer, the desert is characterized by high temperatures and dry air, while in the winter season, the desert experiences extremely low temperatures and precipitation in the form of snow.
There are several factors contributing to the Great Basin's classification as a cold desert, including its more northern latitude as well as its higher elevations which range from 4,000- 6500 feet. The Great Basin Desert is considered the largest in the US and its entire area covers approximately 190,000 square miles (17). Geographically, the basin is defined by vast ridges which are separated by deep valleys and the occasional desert lakes.
Additionally, the basin itself is bounded by two mountain ranges that define its eastern and western borders which include the Wasatch range in the east, and the Sierra Nevada mountain range to the west (17). It is also worth noting that this desert is more seismically active due to expansion of both the Earth's crust in the region, causing the emergence of faults, mountains, basins, and valleys over time, and the presence of the two parallel mountain ranges mentioned earlier, (18). The soil types in the Great Basin Desert include: fine salty soil, shale, and gravel soils deposited by streams.
Image of mountains and valleys in the Great Basin desert, image form Wikimedia Commons.
Image of a sagebrush steppe in the basin region, image from Wikimedia Commons.
Image of snow covered mountains in the Great Basin region, image from the National Park Service.
Despite being a desert, the Great Basin has several sources of water to draw from. One of the major sources of water in the great basin desert comes from groundwater reservoirs (15). These groundwater reservoirs exist under areas of the desert in which prehistoric lakes used to exist. The only way the groundwater is recharged is through seasonal precipitation which primarily comes in the form of snow during the winter season (18). However, because amounts of precipitation are so small, recharging of these reservoirs often takes a very long time .
As the seasons progress and the temperature gets warmer, the snow pack melts and makes its way down from the mountains and into the valleys and lower elevation regions of the Great Basin desert (18). Salty lakes could potentially form, depending on the amount of snow melt from the mountains. However, these are only temporary and can rapidly evaporate due to high temperatures (18). A third major source of water that supplies the various regions of the Great Basin desert are rivers and streams. An example of which is the Humboldt river, whose depths can vary during the year (18). Due to the unique landscape of the basin, it is completely cut off from the ocean meaning that any water that makes it into the Basin is going to remain there unless it's moved by people.
Image of the aftermath of prescribed burning in the Great Basin region, photo from the National Park Service.
Fire plays a major role in the well being of communities in the Great Basin desert. On the one hand, natural fire can act to clear away invasive vegetation, and control the range of both Juniper and Pinyon trees from expanding into sagebrush communities. However, extreme fires caused by excessive fuel loads within these systems can result in the destruction of both sagebrush and the Juniper/Pinyon communities, (14). This clearing can act as the catalyst for the invasion of nonnative plants such as cheat grass (14). It is important to note that the frequency and size of wildfires within the Great Basin region are increasing, partially due to human fire suppression (14).
1) Geology. (n.d.). Retrieved from https://www.nps.gov/deva/learn/nature/geology.htm2) Mojave Desert. (n.d.). Retrieved from https://www.newworldencyclopedia.org/entry/Mojave_Desert3) Mojave desert. (n.d.). Retrieved from https://www.worldwildlife.org/ecoregions/na13084) Salt Flats. (n.d.). Retrieved from https://www.nps.gov/deva/learn/nature/salt-flats.htm5) Stoffer, P. (n.d.). General Geologic History. Retrieved from https://pubs.usgs.gov/of/2004/1007/geologic.html6)National Park Service. (2019, July 5). Sonoran Desert Network Ecosystems.7) Feller, W. (2015, December 1). The Colorado Desert.8) Rutledge, K., Ramroop, T., Boudreau, D., McDaniel, M., Teng, S., Sprout, E., . . . Hunt, J. (n.d.). (2011, January 21). Rain shadow.9) Schoenherr, A. A. (1995). California's Deserts. In R. Benseler, E. Callenbach, R. F. Dasmann, D. MacNeil, & R. Ornduff (Eds.), A Natural History of California (pp. 406-515).10) Gorlitsky, L. (Presenter). (2020, April 2). California's Deserts. Lecture presented at EEB 154.11) The Salton Sea Authority. (2017). Timeline of Salton Sea History.12) Brooks, M. L., Esque, T. C., & Duck, T. (2007). Creosote Bush, blackbrush, and interior chaparral shrublands [Chapter 6]. In: Hood, Sharon M.; Miller, Melanie, editors. Fire ecology and management of the major ecosystems of southern Utah. Gen. Tech. Rep. RMRS-GTR-202. Fort Collins, CO: US Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 97-110, 202, 97-110.13. Baker, Mailing Address: Great Basin National Park 100 Great Basin National Park, et al. Deserts - Great Basin National Park (U.S. National Park Service). www.nps.gov, https://www.nps.gov/grba/learn/nature/deserts.htm. 14. Fire - Great Basin National Park (U.S. National Park Service). www.nps.gov, https://www.nps.gov/grba/learn/nature/fire.htm. 15. Groundwater - Great Basin National Park (U.S. National Park Service). www.nps.gov, https://www.nps.gov/grba/learn/nature/groundwater.htm. 16. Rivers and Streams - Great Basin National Park (U.S. National Park Service). www.nps.gov, https://www.nps.gov/grba/learn/nature/rivers.htm. 17. Great Basin Desert - DesertUSA. https://www.desertusa.com/great-basin-desert.html. 18. Great Basin Geology. NASA Earth Observatory, 27 Feb. 2008. earthobservatory.nasa.gov, https://earthobservatory.nasa.gov/images/8497/great-basin-geology.19. Lovell, Mailing Address: Bighorn Canyon National Recreation Area South District Visitor Center 20 US Hwy 14A, and WY 82435 Phone:548-5406 Contact Us. Great Basin Desert - Bighorn Canyon National Recreation Area (U.S. National Park Service). www.nps.gov, https://www.nps.gov/bica/learn/nature/great-basin-desert.htm.
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