Ca Geology Chp 6

Front 1

Covering more than __ million acres, southeastern CA's deserts encompass as much land as the entire state of Ohio. Makes up about 1/5 of CA's landscape.

Back 1

25

Front 2

A ___ is an area where average evaporation is ___ relative to precipitation, resulting in scarce vegetation and low population. CA's are the result of ___ and ___.

Back 2

desert; high;

location and topography;

Front 3

In most of CA, moist air masses travel eastward from the Pacific Ocean, cooling as they rise over mountains but since cooler air can't hold as much moisture, condensation occurs on the western slopes of the mountains, relieving the air masses much of their moisture. Sierra Nevada and other mountains block moist Pacific air so well that it creates desert. The mountain's ability to do this is called the _____.

Back 3

orographic effect;

Front 4

___ refers to the dry area on the downwind side of a mountain range created because the mountain range forms a barrier to moisture-carrying clouds.

Back 4

Rain shadow

Front 5

The hottest temperature ever recorded in the western hemisphere was 134 degrees at ____ in ____ on July 10, 1913

Back 5

Furnace Creek in Death Valley

Front 6

Chemical weathering of rocks proceeds slowly in the desert because of the lack of ___ and ___. Because decayed plant material is generally absent, ___, which are highly effective chemical weathering agents, are also absent. Without sufficient water to dissolve them, soluble minerals persist at the ground surface & in desert soils.

Back 6

water and vegetation;

organic acids

Hint 6

One of the distinguishing features of a desert is the scarcity of vegetation. Joshua Tree, palo verde, smoke tree, found nowhere else in CA. Near water & higher slopes of some ranges, ground surface is vegetated. However, throughout most of desert, rock & soil at surface are exposed to forces of weathering & erosion.

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Front 7

One major effect of desert weathering is the formation of ____, a black iron and manganese-oxide coating on the rocks. Over tens of thousands of years, the varnish slowly turns the rock surface dark. Early desert dwellers chipped through the coating to carve ___, rock drawings that remain visible in some CA deserts.

Back 7

desert varnish (rock varnish);

petroglyphs;

Front 8

___ is an important geologic agent in desert regions. Strong ones can be generated by local ____ between the mountains the and basin floors of the desert, as well as by more _____. Can carry particles as high as 2 meters above ground.

Back 8

Wind; temperature variations; regional storms

Front 9

One of the features produced by the removal of fine sediment by wind, a process termed ____, is ____. Removal & downward settling of fine particles leaves behind the larger rock fragments. The larger rocks then become coated with desert varnish, and the ground surface becomes armored with the ___. The surface is then protected from further wind erosion, unless the pavement is disturbed by erosion or human impact.

Back 9

deflation; desert pavement; desert pavement;

Front 10

Sand dunes make up a ___ part of even the sandiest desert. Only 2% of the total area in Death Valley. For a sand dune to accumulate, 3 conditions need to be met.

Back 10

very small;

1. Wind speed in area must be adequate to lift & transport sand grains.

2. Little or no vegetation. (Plant roots are effective anchors that stabilize the sand).

3. Sand-sized sediment must be available for transport. (Smooth polished rock surface will not give rise to sand dunes, even in the fiercest winds).

Front 11

Valleys of SE CA ideal for sand dune formation because unvegetated & windy. Sand is picked up by prevailing winds (west to east). As air masses reach the front of the mountain range, the wind speed decreases & the sand piles up against the mountain front.

Back 11

What the flip was grandma doing at the sand dunes?

Front 12

Even in the driest desert, ____ is the primary force that shapes the landscape. Infrequent intense storms (N. from Gulf Mexico) & flash floods are common. Because mountain canyons are __ and __, (water won't soak in ground) flash floods carry large amounts of sediment to the edges of desert valleys (kills people). Here large ___ have been build up.

Back 12

running water;

steep and unvegetated;

Alluvium fans;

Hint 12

Skies in downstream areas can be blue & cloudless so people have no clue.

Front 13

When floodwaters are carried from the steep, confined canyons or ___ (water carved channels) of the mountains onto the basin floors, the water spreads out. As velocity decreases, sediment carried by the stream, usually a mixture of sand and gravel, is deposited at the mouth of the canon. Channels shift back & forth here & after repeated floods, a fan shaped deposit of alluvium accumulates _____. Prominent features. Base of the fan is at canyon mouth, and fan slopes toward the basin floor. The size is proportional to the size of the drainage network that feeds it. Along the front of some ranges, they coalesce along the range front to form a broad, sloping surface known as a ____.

Back 13

arroyos; Alluvium fan; bajada

Front 14

Alluvium fans can be build by flash floods, debris flow, or mudflows. Because all active surface of alluvial fans are vulnerable to periodic floods, construction on fans is risky. Flood could occur once in a century. Magnitude large though.

Back 14

Front 15

Because of high temperature & relatively permeable soil along the mountain fronts, floodwaters from desert mountains quickly evaporate or sink into the desert floor. Even during floods, most streams lack the water to flow beyond the confines of the basin floor. There are ___ a system of streams that converge in a closed basin & evaporate without reaching the sea.

Back 15

interior drainage

Front 16

During major flash floods, the water that runs off from the canyons can cover the basin floor. The water collects in a shallow lake here periodically and are called ___. Without water, the flat basin floors are called ____.

Back 16

playa lakes; playas

Front 17

When no runoff, the water in playa lakes evaporate, leaving behind fine-grained lake sediment & minerals crystallized from the evaporating lake water. Because many of the ____ (salts) minerals are light-colored, the dry surfaces of the playas are __ and highly reflective. They shimmer. sometimes look blue and create mirages.

Back 17

evaporite; white

Front 18

A few of the basins in CA desert contain permanent lakes. ___ used to cover 10 meters deep, but today it is dry. High winds blowing across the dry bed of it generate enormous dust storms. Its dust is worst particulate pollution source in U.S. Contained high levels of toxic elements like arsenic so government began program to cover the lake deposits & stabilize the surface. Cover w/ gravel, vegetation, water.

Back 18

Owens Lake bed;

Front 19

Throughout CA's deserts, have found evidence of landscapes dotted with lakes as recently as ___ years ago. Shorelines can be seen even in places where haven't been floods in a long time. Layers of evaporite minerals & volcanic ash found in areas which means ancient shorelines here but erased by erosion or deposition.

Back 19

11,000

Front 20

Scattered along shores of Mono Lake are clusters of rounded white towers formed of calcium carbonate. From in zones where water from springs that discharge into the lake mixes with the lake water. Spring carries dissolved ___ from nearby rocks & and the alkaline lake water contains ___. Mixes & leads to crystallization of calcite. Algae may play a role. Remain standing even after shoreline has dropped.

Back 20

Tufa; calcium; carbonate

Front 21

Geologists have established the ages of the ancient lakes by carbon-14 dating of scarce wood fragments, shells, tufa deposits, & fingerprinting volcanic ash layers. In basins where lake history has been studied in detail, it appears lakes have grown & shrunk episodically, reflecting major changes in the climate during the past 1-3 million years.

Back 21

Mama look at bubu

Hint 21

Lakes broken up by faulting and lava flows as well as drying up of rivers & lakes.

Front 22

During times of global cooling, when glaciers covered the high parts of the Sierra Nevada, CA's deserts were cooler & evaporation rates were lower. As a result, lakes formed in the valleys of the CA deserts where only playas exist today. The most recent period of extensive lakes ended about ___ years ago.

Back 22

11,000.

Hint 22

Because desert lakes are excellent recorders of past climatic conditions, they are being intensively studied today as researchers attempt to better understand the Earth's global climate system.

Front 23

After gold & silver, people turned their sights to common white covering on the dry lake beds. Discovered ___ and ____. Also third borate mineral ____. These brought prosperity to desert & mined from Death Valley 1882-1928.

Back 23

sodium borates (ulexite/cottonball);

Borax (tincal);

colemanite

Hint 23

Used for alloys, lustrous finish on ceramics, preservative for mean, enamel for bathroom stuff, soap water softener, apothecaries.

Front 24

Borax problem was had to transport along dry steep mountains to faraway areas. No railroads around or water really. Huge weights of borax at a time. Difficult because thin salt crust could make them fall. Found route with thick crust but covered with jagged crystals. Had to chop through it by hand in high temperatures by Chinese laborers. Two story high wagons. 20 mule teams.

Back 24

Yo Mama

Front 25

1913 homesteader John Suckow found colemanite while drilling wells. Area was Kramer Borate District. New mineral discovered Kernite. Eventually this area replaced Death Valley for producing borax. Geologist believe borate here originated from volcanic vents in the area & migrated to the lakes in the circulating groundwater. Borate deposits formed when lake water evaporated to the point that it became supersaturated with borate, causing minerals to crystallize.

Back 25

The process of evaporation and precipitation of minerals is responsible for producing evaporite deposits of several types. Include table salt. In 1990, value of CA's boron minerals was more than $400 million.

Front 26

Large areas of the CA desert are protected as national and state parks & wilderness areas. The desert provinces are an important recreational resource for Californians. Even though areas set aside for operation of off road vehicles damage can be done by stray vehicles. Concern about vegetation & desert pavement being affected.

Back 26

YA'LL NEED JESUS

Front 27

Congress designated __ million acres as California Desert Conservation Area in 1976. 72% owned by federal government.

Back 27

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