Ca Geology Chp 11 Central Valley

Front 1

___ 15 million acres of farmlands are richest agricultural region in history of the world. 1986 ag harvest was worth $14 billion, exceeded the value of all gold ever mined from CA.

Back 1

Great Valley AKA Central Valley

Front 2

___ Valley makes up the northern third of the Great Valley and the ___ Valley makes up the southern 2/3 of the province. Both watered by Sierra Nevada.

Back 2

Sacramento Valley;

San Joaquin Valley;

Front 3

Sotuh of Fresno there is a region of low-lying bottomlands where rivers drain onto the floors of intermittent lakes with the largest being __ Lake.

Back 3

Tulare Lake;

Front 4

Great Valley used to be native grasslands, forests, marshes, home to one of the largest __ populations in North America more than 100,000.

Back 4

Native American populations;

Front 5

Most of Great Valley surface is covered by recent & Pleistocene alluvium. Most from Sierra Nevada in ___ when lots of sediments come pouring in from glacial melting. At least 4 major pulses of deposition took place as this happened.

Back 5

Glacial outwash;

Front 6

Rivers receive sediments when rivers overflow their channels. Sierra Nevada uplifts relative to the Great Valley so rivers are constantly cutting ___. As they cut or incise their channels, the rivers leave behind remnants of the older floodplain surfaces as ___ which are flat and preserve alluvium beneath. With increased elevation above the modern rivers, one finds progressively __ valleys & deposits.

Back 6

downward;

stream terraces;

older;

Hint 6

Front 7

Fertile soils are one of CA's great resources, especially on young alluvial surfaces. Form from geological & biological processes that alter sediment on floodplain deposits. Plant material decays from microbes so organic material is added in upper soil in the form of __. This increases the fertility, changes texture of soil, & increases mineral weathering. This soil horizon characterized by organic matter is known as __ horizon where there is maximum biologic activity.

Back 7

humus; A horizon;

Front 8

As water goes down A horizon, it becomes acidified by the organic acids and so beneath the A horizon is an area where chemical weathering breaks down __ minerals. Water also carries clay, iron oxide, & salts lower. As you go further down, area becomes more red as iron oxide rusts. The soil horizon characterized by the accumulation of one or more weathering products is known as __ horizon. These are zones with the greatest weathering activity.

Back 8

silicate;

B horizon;

Front 9

Since B horizon processes form __ than organic processes in A horizon, young soils will display A horizon, but not B horizon yet.

Back 9

slower;

Front 10

In some parts of the valley, older solids have developed __, hard layers formed by the accumulation of silica, iron, or calcium carbonate. Oldest soils found high terraces.

Back 10

hardpans;

Front 11

The type of soil that forms and the depth and rate of it depends on what?

Back 11

1. Climate,

2. Organisms present,

3. Topography,

4. Nature of rock/deposit AKA parent material,

5. Time elapsed since the surface formed.

Front 12

One of CA's most agriculturally productive soils is ___ soil series in Great Vallely. Found in half million acres of CA & designated as CA's state soil. Well developed B horizon & silica hardpan 1 meter below. Have __ found on older high terraces. The mounds & depressions probably from weathering & burrow animals. Shallow depressions create rare habitat called __ where animals come like fair shrimp.

Back 12

San Joaquin soil series;

mima mounds;

vernal pools;

Hint 12

Front 13

Intensive agriculture & irrigation has created water quality problems from high levels of nitrates, pesticides, & herbicides in streams. Arid regions have soluble minerals, calcium carbonate, sulfates, & other salts, accumulate in lower part of soil profile where percolating water evaporates. Buildup occurs because rainfall can't dissolve it through soil. Thus, salinity is high and selenium bearing minerals.

Back 13

I guess...

Front 14

Irrigation of arid soils causes salts to be dissolved & carried to the lower horizons at a higher rate than would occur under natural conditions. Clay layers are problem because allows build up for __. __% of soils damaged by buildup of salts. Salinization can inhibit plant growth, damage, leaves, & crops.

Back 14

salt; 10%

Front 15

One solution for salinization is installation of subsurface __ beneath fields to carry off salt-laden irrigation water. 1970s ___ was built to carry ag drainage water from fiends north of Kesterson Reservoir to Los Banos but found it had high ____ above drinking water standard.

Back 15

drains; San Luis Drain;

selenium;

Front 16

There are __ chemical elements essential for plant growth. 3 carbon, oxygen, hydrogen come from atmosphere. Others from plant roots that get organic matter & mineral weathering. Selenium & iodine are necessary for many animals but NOT for plants. If too little, can lead to disease or death, but too much can be toxic.

Back 16

16 chemical elements;

Front 17

Rising dramatically from the flat floor of Sacramento Valley is __are the major topographic feature of the otherwise nearly flat valley. Has a Castellated Core (looks like castle) surrounded by low circular easily eroded sedimentary rocks called the moat. Volcanic activity here from the intrusion of silica magma during ___ into Mesozoic rocks. Volcanic eruptions of silicic & intermediate. First ones formed ___ 1.6 mya dome along the ciricular system of faults that underlie the moat. Finalvolcanic activity formed core group of __ domes. In cneter of Core is thick section of sediments that filled a deep crater lake during the eruption of the pyroclastic flows. All activity stopped __ million years began.

Back 17

Sutter Buttes; Cenozoic;

1.6 millions years ago;

rhyolitic;

andesitic;

1.3 million years ago;

Hint 17

older parts are more silicic while younger are more andesitic.

Front 18

Beneath the Cenozoic alluvium of the Great Valley lies thick old sediments & rocks. Creates a sedimentary basin. It is deeper on the __ side 20,000 meters. Also steep & upturned. __ side is more gentle.

Back 18

western; eastern;

Front 19

The Mesozoic & Cenozoic rocks of the Great Valley known as the ___ consist of sandstone, shale, & conglomerate. Marine fossils & sediments show they accumulated in an ocean basin that was west of the Mesozoic North American margin. __ side rocks are from deltaic & shallow water while the __ are deep ocean floor by turbidity currents. The shoreline of the ancient ocean basin lay along the western edge of the Sierra Nevada.

Back 19

Great Valley Sequence;

east;

west;

Hint 19

check picture on phone

Front 20

The sedimentary basin where the Great Valley sequence accumulated was a __ sandwiched between the Sierra arc & Mesozoic subduction zone. Similar ones in other places between volcanic arcs & ocean trenches.

Back 20

forearc basin

Front 21

Sandstone in older lower formations have volcanic rock fragments eroded from the Jurassic & early Cretaceous Sierran arc. Proof that volcanic chain was there but now eroded from Sierra Nevada during Jurassic & Cretaceous.

Back 21

Volcanic fragments proof of volcanic chains now gone from Sierra Nevada.

Front 22

152 mya marine sediments accumulated in a forearc basin between the subduction zone west of North America & Sierra Nevada volcanic arc. These sediments make up the ___ which is 20,000 meters thick beneath the Great Valley. Rocks of the ___ have been exposed by uplift & titling along the western edge of the Great Valley.

Back 22

Great Valley Sequence;

Great Valley Sequence;

Front 23

During Cenozic time, the Great Valley sedimentary basin became filled with sediment, & the Great Valley emerged from the sea about 24 mya in the Sacramento Valley. The Great Valley Sea persisted in the San Joaquin Valley until __ million years ago.

Back 23

2 million;

Front 24

3 mya the San Joaquin basin was a large embayment in the coastline. Today, it still persists as a lowland and site of Great Valley's lake basins. About 1 million to 600,000 years ago, after San Joaquin Valley closed off from Pacific Ocean, a large lake occupied most of area. ___ clay is evidence for history of Sacramento San Joaquin river system. Contains Pleistocene fossils typical of shallow lakes.

Back 24

Corcoran clay;

Front 25

___ half of Central Valley where sediments are thinner, the sediments of the Great Valley sequence were deposited on igneous & metamorphic rocks of western ___. Further north the Great Valley rocks were deposited on the ___. These relation proof that Great Valley forearc basin lay west of North American continent when the Great Valley sequence was deposited.

Back 25

Eastern;

Sierra Nevada;

Klamath Mountains;

Front 26

___ Great Valley where rocks have been tilted steeply & exposed show Sourth Fork of Elder Creek with mudstone of Great Valley deposited on sedimentary breccia with angular clasts of mafic & ultramafic rocks. Uncomformity because period of erosion between the two. Great Valley oldest rocks contain Buchia fossils.

Back 26

Western

Front 27

At the western edge of the Coast Range ophiolite, where it borders the rocks of the Coast Ranges is a major fault system known as the ___. It separates rocks of Great Valley sequence from Franciscan complex. Many believe it marks the line along which oceanic rocks were thrust underneath the western edge of the forearc basin.

Back 27

Coast Range fault

Front 28

Soils formed on the modern & ancient alluvium of the Great Valley show a progressive degree of profile development. Soil & landscapes formed on the older alluvial terraces are home to vernal pool.

Back 28

Today the lowlands of the Great Valley are subject to periodic flooding by the Sacramento & San Joaquin Rivers & their tributaries.