California

California Geography

Study Guide 2: California Landforms

Geographers are interested in landforms. They comprise the field of action on which the human drama is played, as well as providing opportunities for and imposing limitations on human activity. Here are a few of the questions geographers might ask about the landforms of California.

What kind of landforms are there?

Where are they located?

What has caused various types of landforms, and why are they located where they are?

What influences have these landforms exerted on human settlement patterns, land use, livelihood, and other activities?

Topographic Contrasts

California contains both the highest point in the 48 contiguous states (Mount Whitney, 14,498 feet) and the lowest point in the Western Hemisphere (Death Valley, - 282 feet). The observer will also note various types of mountain ranges caused by different geologic processes, as well as narrow canyons and broad plains. Geographers have identified 11 different physiographic (landform) regions. You'll need to know these regions so that you can locate them on a map quiz and identify some of their significant characteristics on your first midterm. I will briefly describe each of them, including some of their outstanding features. Refer to the link below in order to study the location of these physiographic regions.

California Landform Regions

Sierra Nevada: Several coalesced batholiths, primarily made of granodiorite. This intrusive igneous mass experienced normal faulting with westward tilting along its eastern flank. Hence the western, or windward, slope of the range gradually rises to the crest, which lies along eastward edge of the range. The eastern, or leeward, slope rises steeply along a fault zone, in some places forming an almost vertical wall. The granitic core of the Sierra was emplaced as the eastern Pacific seafloor was subducted beneath the edge of the North American continent some 200 million years ago. Subsequent uplift and erosion of 35-50,000 feet of overlying rock exposed this granitic core about 65 million years ago. Since then erosion by rivers and streams and by glaciers has carved deep canyons into the western slope.

Yosemite National Park Ð'- Sierra Nevada Geology

Klamath Mountains: A series of complex geologic structures composed of seafloor deposits that have been welded onto the western edge of North America during subduction. This process produced a melange of sedimentary rocks from the seafloor, volcanics and upper mantle rock from the oceanic crust, and metamorphic rock from the subduction zone. Subsequently, a batholith was emplaced from melting of the subducted plate. During the last 2.5 million years these peaks have been carved by glaciers on several occasions, producing the scoured, sharp-edge peaks and ridges and the deep, U-shaped valleys.

Peninsular Ranges: Another series of granitic batholiths that form the spine of the Baja California Peninsula. These intrusive igneous rocks are also associated with subduction along the western edge of North America. Mt. San Jacinto at the far north end of the range is its tallest peak at over 10,800 of feet. It towers over the resorts of the Coachella Valley in the Colorado Desert.

Southern Cascade Range: The south end of the chain of volcanic mountains that extend northward through Oregon and Washington as far as Mt. Baker. This range includes such well-known peaks as Mt. Rainer, Mount Hood, Mt. St. Helens, and Crater Lake. In California the two most prominent peaks are Mt. Shasta and Mt. Lassen. Mt. Shasta is a stratovolcano formed by alternating layers of volcanic ash and cinders and lava flows. Mt. Lassen is a plug dome, the world's largest, extruded out of the collapsed caldera of prehistoric Mt. Tehama.

Transverse Ranges: A complex of folded sedimentary rock and granitic batholith associated with the bend in this San Andreas Fault. Coastal Southern California lies on the Pacific Plate moving northwest in relationship to the North American Plate. As a result of the westward bend in the fault, the Pacific Plate collides with the North American Plate buckling the crust upward. Granitic rock at the eastern end of the range culminates in two high peaks, Mt. San Antonio (Old Baldy) over 10,000 feet, and Mt. San Gorgonio over 11,000 feet. The Transverse Ranges are the only major landform in California with an east-west orientation.

Modoc Plateau: Layers of basalt lava flows broken by normal faulting. Basalt forms from very hot, fluid magma rich in iron and magnesium. Is a heavy, dark rock. This landform is related to the Columbia Plateau, which covers much of central and eastern Washington and Oregon. The Modoc Plateau is a raised surface from 3500 to 5000 feet elevation. Because of the highly porous nature of the basalt and cavities left underground that were vacated by flowing lava, this region exhibits numerous large springs with short creeks and rivers resulting. Fall River and Tule River are examples.

Basin and Range: A series of parallel, north-south trending short mountain ranges and intervening basins. A normal fault marks the transition from the rugged, steep-sided ranges to the gently sloping or almost level basins. The Basin and Range is an example of horst and graben topography, down-faulted blocks that form basins with internal drainage, and up-faulted blocks that form ranges. Since this region is in the rain shadow of the Sierra Nevada it is largely desert. With little vegetation to impede erosion, the flanks of the ranges are gouged by dry washes, or arroyos. The material eroded from these arroyos is deposited at their mouths to form alluvial fans, and farther out in the basins. After a cloudburst passes an intermittent lake collects in the lowest point. Since these basins have no outlet, salts dissolved in the water from intermittent streams accumulate on the dry lakebeds to form glittering salt pans, or playas. This region extends from the eastern Sierra Nevada across Nevada and Utah to the Wasatch Mountains.

Coast Ranges: A series of parallel ranges and valleys stretching along the coast from the Transverse Ranges north into Oregon. As the seafloor subducted under North America the edge of the continent scraped material from the ocean bottom and attached it in long folds. The Coast Ranges are composed of sediments scraped from the floor of the ocean, basalt, gabbro, and peridotite from the oceanic