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The Basin and Range in Nevada abruptly terminates against the Sierra Nevada, rugged glaciated mountains pushed up from the crust as a tilted block whose western side continues as a structural basin (Sacramento and San Joaquin Valleys) now filled with erosion debris from the mountains. More inwash comes from the Coastal Ranges, a recent series of folded/faulted mountains pushed up by the east-moving Pacific Plate against this western edge of the North American Plate (now complicated by lateral movements along the San Andreas and other faults). Our journey ends in San Francisco but we also look at Coastal Ranges and the Cascades in Oregon and Washington.


The Pacific Coast: The Sierra Nevada Range; The San Francisco Bay Area, CA; The Cascades; Seattle, WA;

Our imaginary flight finally nears the Pacific Coastal and Interior Mountains in California. These units are part of a vast array of folded mountains, tilted blocks, and accreted terranes that extend from Baja California on the of the North American tectonic plate to well into western Canada northward into southern Alaska. The map below shows the major terranes that were driven onto the western edge of the North American continent. The nature of these terranes is discussed in detail in Section 17, starting with page 17-6. It is worth noting here that all of the western continental edge is an active plate margin: from San Francisco southward the boundary is complex, involving a failure to subduct so that movement is lateral along fault systems (San Andreas et al.); from northern California over most of the remaining coast into Alaska, the boundary is of the subduction type (mostly of the Pacific plate, but from California to southernmost British Columbia a small separate oceanic crustal block, named the Juan de Fuca plate, is subducting and causing the volcanoes of the Cascades to be emplaced.

Map of accreted terranes

This map shows the major subdivisions of the Pacific Ranges:

Physiographic Divisions of Pacific mountain ranges and valleys.

Since we will concentrate on California, with the final destination being San Francisco, we will set up a geologic framework for that state using this map.

USGS Geologic Map of the State of California.

The size of print in the Legend is too small to read. Red refers to granitic rocks, greys to metamorphic rocks, blue to Paleozoic rocks, various shades of green to Cenozoic rocks in the Coast Ranges, and pink to volcanic flow units in the northeastern part of the state.

We proceed across the Sierra Nevada Range, the large, strongly glaciated tilt block of crust composed mostly of igneous and metamorphic rocks associated with numerous interpenetrating batholiths. This mountain range rises precipitously to 4,421 m (14,494 ft) at Mt Whitney - the highest point in the 48 states - on its east side (south of this scene). The east side tends to be steep-fronted, being fault-bounded, whereas the western slopes are gentler in inclination, although still deeply dissected by streams. The scene below shows off the northern Sierras with Reno at top center, volcanics in the westernmost Basin and Range appearing in bluish tones, Lake Tahoe nestled in the High Sierras, and many deep valleys. Dark firs and other vegetation persist up to about 2750 m (9000 ft), above which trees are absent and rock bare (light tan).

Landsat-1 view of the Sierra Nevada ramge, September 1972

The eastern front of the Sierras rises steeply from the Owens Valley to its east. This image was made by combining a SIR-C image with topographic data derived from its altimeter:

The eastern side of the Sierra Nevada and part of the Owens Valley near Bishop, California.

In the high country, glaciation has carved out deep canyons and rugged landscapes. This ground view of the Kings Canyon National Park area to the south is typical.

The Kings Canyon area in the Sierra Nevada batholithic complex.

We then pass west over rolling ground in the Sierra Nevada Foothills across the Central Valley into the Coast Ranges around the San Francisco Bay area, all shown in this October, 1972 Landsat image.

October 1972 Landsat false color composite of central California, including San Francisco, the Coast Ranges, and the Sacramento Valley.

Most of the landmarks we describe next, we can see in this high-altitude aerial oblique image taken by a camera onboard a NASA U-2 aircraft. The view from this perspective looks east-northeast from a point over the Pacific Ocean. In the distance are the snow-capped Sierra Nevadas and the Sacramento Valley. Try to match specific features in this IR photo (which, incidentally, is blue-dominated because the sky blue effect was not compensated by a haze filter) with their counterparts in the Landsat image.

 Color infrared photo taken from a U-2 aircraft showing the San Francisco Peninsula, the bays inland, and part of the Sacramento Valley, with the snow-capped Sierra Nevada in the distant background.

The Central Valley, known in its northern half as the Sacramento Valley (the southern half is the San Joaquin Valley), is one of the great agricultural regions of the world. The numerous farms visible in the above imagery attest to this dominant land use. Cash crops include beans, cotton, rice, barley, and sugar beets. Stockton and Modesto are the two large valley towns.

The Coast Ranges are the most recent products of still active orogeny that results from the collision of the Pacific and North American lithospheric plates. The mountains consist of granular (clastic) sediments in places metamorphosed by high temperatures and pressures or intruded by igneous magmas. Their rocks have been severely deformed, but the ranges generally rise only a few thousand feet above the Pacific sea level. Passing near the coast but inland is the great wrench (horizontal movement) fracture known as the San Andreas Fault (look for the abrupt termination of red [from California oaks, redwoods, and other vegetation] in the mountains south of San Franciso), which is the plane dividing the north-moving Pacific side of the fault from the more static North American side.

Two coastal bays stand out in this image: Monterey Bay near the bottom (noted for its rich aquatic and bird life) and San Francisco Bay, which to its north becomes San Pablo Bay, along which San Francisco (west), Oakland (east), San Jose (south) and many other Bay Area towns are situated. The fault-bounded hills to the east are part of the Diablo Range, which becomes progressively less vegetated towards the Great Valley (at this time of year it is covered with the same brown, dried grasses we examined in the Morro Bay subscene).

Most of San Francisco appears in grayish-blue tones that indicate a sparsity of trees in the city (rather surprising to any resident or visitor who is struck by its great beauty). The exceptions are the lush vegetation (many eucalyptus trees) in Golden Gate Park (long rectangle) and the Presidio (a now deactivated military facility). Your monitor resolution may allow you also to pick out a tine (blue) line of ships (mothballed Liberty Ships and others from World War II) right of the narrow Carquinez Straits off the east end of San Pablo Bay.

In the southern part of the Bay are large patches with lighter blue or green tints. These are salt evaporating basins. The greenish ones are actually basins with red sediments (bright tones in Thematic Mapper band 3 that thus pass green light in a transparency). A closer look at these basins is afforded by the MISR sensor onboard the Terra spacecraft; compare this with the second image below:

MISR subscene showing evaporation basins at the southern end of San Francisco Bay.

Many, including this writer, consider San Francisco to be the most beautiful city in the U.S. Here is a photo taken in 1994 by the writer that shows the central city from the tourist vista called Twin Peaks.

Color photograph of San Francisco from Twin Peaks, 1994.

Lets take a closer look from space by enlarging the Bay Area portion of the full Landsat image.

False color Landsat closeup of the Bay area.

6-12: In the above subscene, find Berkeley, Oakland,Hayward; San Jose; the San Francisco Airport, Palo Alto, and Mount Diablo (near to which the writer lived for 2 glorious years). ANSWER

We carry this enlargement even further to highlight the most famous bridge leading into the Peninsula from the north, the Golden Gate Bridge. The view of "the City" through the bridge (lower image) is from the vantage of a small park on the Marin County side (at X in upper image). The Presidio and Golden Gate Park are also obvious.

False color Landsat subscene of part of San Francisco and the Golden Gate Bridge.

Color photograph of San Francisco looking through the Golden Gate Bridge.

San Francisco is equally impressive when looking at its east side, across the San Francisco Bay:

San Francisco and the Bay Bridge.
Courtesy: Carolina Map Distributors

A most remarkable image of downtown San Francisco with its many tall building (some visible in the above photo) has been taken by the commercial IKONOS satellite (SpaceImaging, Inc.). This color version has a spatial resolution of 2 meters:

Downtown San Francisco as imaged by the camera on the IKONOS satellite.

Before taking leave of the City by the Bay and central California, we present one more interesting Landsat image. It shows the Bay area clear of fog (normally in summer fog rolls in every day) but the Great Valley to the east is entirely fog shrouded. This is the so-called tule fog that often develops inland under the right meteorological conditions. Note that this fog has spilled over the low pass where Highway 50 crosses the eastern Coast Range into the Livermore Valley to the west.

Landsat image showing the tule fog condition in the Central Valley of California; the Bay area remains fog free.

The above has introduced you to California - a fabled place both the Americans and to the world at large. With its 38 million people, its development has made the state the 5th largest economy in the world. Lets take a look at the entire state as seen in one of the early Landsat mosaics made by the General Electric Space Division lab near Beltsville, MD.:

Mosaic of Landsat images covering the entire State of California; the western part of Nevada appears to the right of the black line border.

California contains active volcanoes. Mt Lassen in the Cascades at the north end of the Sierra Nevadas erupted in 1915. One of the most beautiful of all Cascade Volcanoes is Mt. Shasta (the larger white patch near the top) seen here in a photo taken from the ground looking north:

Mt. Shasta

From this and other data sources, a first-order Landuse/landcover map of the state was produced by the NASA Ames Research Center in cooperation with the NASA Jet Propulsion Laboratory. Here it is (admittedly hard to read at this screen scale):

Land Cover Map of California.

JPL has a short survey of the various ways that California has been monitored from space. Access through the JPL Video Site, then the pathway Format-->Video -->Search to bring up the list that includes "California from Space", September 6, 2003. To start it, once found, click on the blue RealVideo link.

We have explored Southern California in various pages elsewhere in this Tutorial.The areas in and around Los Angeles were emphasized. On this page we will show 3 SIR-C SAR radar images (Endeavor missions) that extend the coverage. First is the southern part of the Greater Los Angeles region, showing towns such as Anaheim and Huntington Beach in Orange County in the lowlands next to mountains.

Orange County radar image.

Off the shores of Southern California are several large islands, sometimes referred to as the Channel Islands. These are actually the above sealevel tops of largely submarine mountaneous protrusions on the shelf. Santa Cruz Island lies just south of Santa Barbara.

Santa Cruz Island.

Whoa! Some viewers of this Tutorial who live in the Pacific Northwest may feel slighted in that we haven't shown any imagery so far that covers their fast-growing region. We can ameliorate this seeming oversight by allowing our airplane to change course in Nevada and head northwest into Oregon. The view below is a mosaic (production of this type of composite scene is treated in the next section) of images covering most of the western halves of Oregon and Washington:

False color mosaic made from Landsat images showing nearly all of western and central Oregon and Washington, including the cities (in blue) of Portland and Seattle.

The large river that divides the mosaic is the Columbia which is also the state border between Oregon and Washington. The near vertical set of white patches marks snow found on the higher elevations of the Cascades. The large patch in the Oregon Cascades is Mount Hood. North of the river are Mount Rainier and Mount St. Helens, among the numerous active and dormant, variably eroded, stratovolcanoes that make up the High Cascades. In northwest Washington is an E-W body of water off the Pacific Ocean that ends to the east with various islands and several inlets including the N-S Puget Sound along which Seattle is located. Near the upper left is the Canadian island of Vancouver. From the Cascades westward the land is heavily wooded (including abundant firs and evergreens), as indicated by the widespread reds. East of the Cascades, the land is sparsely covered by trees - a consequence of the rapid reduction in rainfall as clouds pass over the Cascades, dumping their moisture, and producing a so-called "rainshadow" that creates a semi-desert ecosystem.

One Landsat scene in southern Oregon (just below the bottom of the mosaic) contains several features of special interest both within and east of the Cascades. Look:

Landsat-1 image containing Crater Lake.

The focal point in this scene is the circular lake known as Crater Lake. This 12 km wide (8 miles) lake lies within a volcano, known as Mt. Mazama, that collapsed and erupted violently about 10000 years ago, perhaps before humans lived in the region. Thick ash beds resulted - much more than expelled from Mt. St. Helens. Here is an astronaut photo of Crater Lake taken from the International Space Station:

Crater Lake from space.

Klamath Lake lies near the bottom. The blue lake to the east is Summer Lake. The Great Sandy Desert (dark blue) is a series of volcanic flows that are roughly coeval with the Snake River Plains to the east.

When the writer first saw this image, he was struck by the conspicuous large elliptical feature northeast of Crater Lake. It resembled a huge volcanic caldera. Visiting it in 1966 during a field conference, the western part known as the Walker Rim was a cliff composed of volcanic flows. Solid evidence for a caldera was not obvious. This may be a coincidental artifact of several topographic features that because of vegetation distribution gives the impression of ellipticity.

Portland, Oregon lies within the land between the confluence of the Willamette River and the Columbia River. Here this is seen in this Landsat-5 (RGB = 542) image taken on March 6, 1992

Portland, OR, Landsat-5 image.

Looking east, Portland's skyline is beautifully enhanced by Oregon's tallest mountain, Mt. Hood, a stratovolcano:

Portland, OR from the hills, with Mt. Hood in the background.

And finally let us look for a moment at Seattle, Washington, and the islands to its west, most hosting residential areas, as seen first in this ASTER image and then in this aerial photo of the waterfront looking northeast:

ASTER view of the Seattle, WA region.

Panorama of Seattle; note the Space Needle; Mount Hood is in the right background.

Courtesy: Carolina Map Distributors

With these scenes, we end our transcontinental sojourn across the 48 contiguous United States. If you have crossed the states before, you can use this tour as a reminder of what you saw. If such a trip is in your future, this tour is a splendid preview of what you could look for. Bon voyage!

But wait! You should really be aiming to become a world traveler. For the U.S., there already is an Atlas of Landsat scenes covering the 48 contiguous states. Would be nice to have a World Atlas composed of Landsat images (except, since up to 11000 are needed to cover all land areas, such an atlas would have more pages the a multi-book Encyclopedia; we recommend using only images for areas where you expect to spend a lot of time). To affirm that you have now the skills needed to "geographically locate" a Landsat image, we are going to give you another (littler) test. On the next page are 8 full and four partial Landsat scenes, taken from all (except the Antarctic) of the other continents besides North America. They are labeled from A to H. Using any means at your disposal (but a World Atlas is best) try to locate each scene. To help you in this, we will put a few key word hints beneath each image.

As a further aid to this recognition test, we will present an unidentified image on this page, give you a chance to locate/identify it, and then at the top of the (next) quiz page, the writer will walk you through the process by which he was able to determine the identity of this scene. All we will say at this point is that this is a MISR image (Section 16) and that it is deliberately oriented such that North is not at the top, as an added challenge.

So, to proceed with the game, press "next". This will get you in the proper frame of mind to then pass onto the second part of this Section, which is the travelogue through the continents that helps you, through looking at various characteristic cities and landscapes, to gain a perspective on the wide varieties of scenery that make up the land surfaces of planet Earth.

 

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Primary Author: Nicholas M. Short, Sr. email: [email protected]