Chapter 10: The Great Central Valley

Starthistles: Naida Blevins, Miriam Koppel, Tammy Rease, Amber Shrum
November 24, 2002


The Great Central Valley, also referred to as the Central Valley or the Great Valley, is an elongated depression that lies between the Coast Ranges and the Sierra Nevada. It is about 430 miles long and about 75 miles wide. At its extreme northern and southern ends, the elevation is about 400 feet. At its center, east of San Francisco Bay, it is slightly below sea level.

The Great Central Valley is actually two large valleys lying end to end, each drained by a major river. The Sacramento Valley is drained by the Sacramento River and the San Joaquin Valley is drained by the San Joaquin River. The confluence of these two rivers occurs east of San Francisco Bay. This area, the Sacramento-San Joaquin Delta, was formerly a massive wetland. It is now one of California’s important agricultural areas.

This geomorphic province has more than any other been altered by activities of humans. It its pristine state, it contained three primary communities of plants and animals: Valley Grassland, Freshwater Marsh, and Riparian Woodland.

The Great Central Valley is one of California’s arid regions. As such, it shares many characteristics with the desert provinces.



The climate of the Great Central Valley promotes widespread grasslands. Precipitation occurs during winter months, but it is reduced because of the rain shadow of the Coast Ranges. To the north, in the Sacramento River Valley, average annual precipitation is moderate. To the south it is reduced to desert proportions.



The Great Central Valley is a huge basin filled with sediments. Sands and gravel over 30,000 feet deep lie upon Sierran basement rocks that extend downward at an angle from the western slope of the Sierra Nevada.

During the last 5 million years, sediments accumulated as alluvial deposits washed out of the mountains. These deposits are only a few thousand feet deep over most of the valley floor. Depths up to 10,000 feet occur in some places, indicating that the valley floor was not always as monotonous as it is today.

Trapped beneath the sediments of the San Joaquin Valley is one of California’s richest oil fields. Oil has been the keystone of Kern County’s economy since the 1920’s. Unfortunately, San Joaquin Valley crude oil is very thick, making it a high-cost, low-price product. When oil prices drop, it is not economically feasible to pump oil in the San Joaquin Valley.



Valley Grassland

Valley Grassland once covered all well-drained areas in the Great Central Valley as well as larger valleys in the Coast Ranges and cismontane southern California. Even in its disturbed form, Valley Grassland is still one of California’s most common communities, covering over 22 million acres of land.

Pristine grasslands also contained annual grasses and herbs, although the annual grasses were not as abundant as the perennial forms. Some of the wildflowers produced displays of color that are legendary. Among these wildflowers were numerous annual species of geophytes.

The most spectacular of the wildflowers are lupines; California Poppies, and Purple Owl Clover. Other carpets of wildflowers may include various members of the sunflower family. Among these are small species such as Goldfields that occur in untold millions.

Tarweeds and thistles bloom long after the grassland becomes dry. By blooming during summer, they capitalize on a lack of competition for pollinators. Common Tarweed stands about 2 feet high. These plants have glandular hairs that produce a tarlike substance. This resinous material helps to retard water loss during the long, hot summer. Thistles are prickly plants that usually have purple flowers. The Artichoke Thistle was introduced in the 1920’s from Europe, where it is used for food. It first appeared near Benicia in the inner Coast Ranges and has spread into overgrazed areas of the western Great Central Valley. If harvested in the bud stage, this plant provides an edible artichoke. Cattle and sheep avoid it, so one it becomes established, it spreads rapidly to infest entire pastures. Its beauty is the only redeeming feature of overgrazing.


The Valley Grassland ecosystem of The Carrizo Plain is home for some of the Great Central Valley’s endangered species. It contains native Valley Grassland in a relatively undisturbed condition. 82,000 acres of this region has been purchased by the Ca. Nature Conservancy and are working to restoring it to its original condition.

The Corral Hollow, another valley southwest of Tracy, has been used for grazing sheep and cattle and a motorcycle playground. A portion has also been the site of nuclear testing. Now it is a 99-acre ecological reserve. It is 30% riparian habitat and 70% grassland. It is home to many reptiles and amphibians. The Corral Hollow also has serpentine soil and the endemic plants associated with the soil type. It is also host to the Large Flowered Fiddleneck, a state and federally listed endangered plant.


Vernal Pools

Vernal pools or "hogwallows" occur where the hardpan is close to the surface. In the Central Valley there are three types of vernal pools: valley pools, pools of volcanic areas, and terrace pools. Merlin's Grass, a spore-bearing plant is abundant in vernal pools. It is an aquatic plant that uses crassulacean acid metabolism, a photosynthesis typically associated with drought-adapted succulents. It helps to conserve CO2. Valley pools are common in the basins or valleys of low-lying areas of saline or alkaline soils. Volcanic pools are similar to terrace pools in flora. They occur throughout the state. Terrace pools occur on ancient flooded terraces on higher ground. Rainwater accumulates because it cannot absorb into the ground. It is surrounded by wildflowers in the spring as it recedes in the spring. Because they are ecological islands there is a great deal of endemism. "Mima mounds" occur in these areas. They are mounds of up to 6 feet and in the low spots are vernal pools. Wind deflation of old stream channels and soil build up around shrub fields are believed to be the contributing factors. There has been a significant decline in the number of vernal pools in California.


Freshwater Marshes

The Great Central Valley had many wetland habitats that were created from mountain runoff. Wetlands are characterized by a mixture of water and emergent vegetation. They are termed swamps, marshes, and bogs. Swamps have the most open water and plants located in swamps are able to withstand submergence of their roots by water. Swamps do not occur in California. Bogs have the least amount of water. They are soggy or supersaturated substrates. They are very acidic and the plants in bogs are nutrient deficient. They water in these locations is often brown because of decay.

Freshwater marshes are the result of the accumulation of water in the shallow depressions of flatlands. They are no longer common in California. Before the ecologic disruption of draining and damming, there were three large lakes in the Central Valley: Tulare Lake, Buena Vista Lake, and Kern Lake, which were connected to or contributed to marshes.

Covering more than 700 square miles, Tule Lake was the largest freshwater lake west of the Mississippi. Freshwater marshes throughout the state were similar. As a reserve, the Creighton Ranch Reserve demonstrates what a marsh system was like. Vegetation is distributed in bands. Plant species occur in single-species zones as bands on the edge of water. Macrophytes "large plants" float in the water and closer to the shoreline are rooted macrophytes and then rooted plants occur in shallow water and on land.

Freshwater marshes are dominated by reeds that grow in water-saturated soils. They fall into 4 categories: Rushes, Bulrushes, Sedges, and Cattails. They are all similar in their grasslike appearance. Cattails cannot tolerate deep water so they occur on the outer edge of marshes. Sedges and rushes are different in that sedges have triangular stems and rushes that round stems. Bulrushes "tules" are related to sedges.

Water loving trees such as willows occur farther away from the water than the previously mentioned plants. The Black Willow is most common in the San Joaquin Valley. Some willows resemble large shrubs. Seeds are dispersed by wind.

Shrubs, such as mule fat occur on higher ground where water is more alkaline. They resemble willows but are in the Sunflower family. Their flowers are small and white and there seeds are dispersed by the wind.

Plants that grow within the marshes are Watercress, a low-growing aquatic plant that emerges slightly above the water. It decomposes rapidly. Floating plants include the Water-fern and duckweeds. Water-fern contain a blue-green alga, which is important in nitrogen fixation and enriches the marsh environment. Duckweeds appear as floating leaflike structures that cover the water. It contributes to the supply of detritus. Non-native floating plants like Water hyacinth also occur. It remains afloat due to their inflated leaves. When in bloom, blue flowers are displayed. These non-native plants are renowned for their rapid growth and rapid rate of absorption of dissolved nutrients.

The Yebra Mansa (Anemopsis california) a member of the lizard-tail species found where the water may be somewhat alkaline. It grows in soggy ground and in localized masses from inland valley to estuaries all throughout the state; its petals are white. It has been used in healing disease of the blood and the skin.

Watercress (Rorippa nasturiumaquaticum) is a low-growing plant that grows in open water. Watercress is an edible member of the mustard family it flows on the top of cold flowing water. The Water-fern (Azolla filiculoides) also grows on the water it is a mosslike fern. It is harvested in some areas for cattle feed and fertilizer. Small floating leaf like plants are Duckweed, they cover the water entirely. Both Duckweed and Water-fern are covered with nitrogen-fixing bacteria that helps to enrich the marsh ecosystem.

Non-native water floating plants are the Water-hyacinth (Eichhornia crassipes) the stems of the leaves are inflated and that is what keeps them afloat. They absorb dissolved nutrients very rapidly and there is thought of growing them near sewer outfalls where they can absorb the nutrients. The Yellow Pond-lily (nuphar polysepalum) like slow-flowing water in the northern part of the state. The problem with all non-native plants is that they can crowd out native plants.

Marsh ecosystems are some of the most productive in the world because of their massive biomass production and all of the elements of detritus, microorganisms and absorption of nutrients.


Marsh Animals

Because of their high productivity marsh ecosystems can support large biomass of consumers. The consumers can not feed on the vegetative parts of the plants thus most of it results in detritus. Birds feed on the abundant seed crop it the upper canopy of the marsh. The dense foliage provides shelter for birds and small invertebrates.

The birds are the most obvious residents of the marsh. Swans, geese, ducks and shorebirds visit the marshes in the Great Central Valley. The number of these birds has decreased due to human activity. Birds that occur in Freashwater Marshes also occur in Saltwater Marshes.

The mammals in the marsh area are few in number. Most species come to the marsh for watering. The Muskrat (Ondatra zibethicus) is one true resident of the marsh, they are about half the size of a house cat, and feed on rushes, tule and cattails. They make their dens out of the plants in the area, most have underwater entrances. Muskrat fur is of average quality and sole as "Hudson Seal", it was introduced in parts of the state for its fur. They are also edible the meat being sold as "marsh hare".

Beavers (Castor canadensis) inhabit streams and lake mainly but can be fund occasionally in the Sacramento-San Joaquin Delta, they live in burrow in the levees.


Riparian Woodland

Riparian Woodland occurred in the Great Central Valley, called gallery forests they are boarded by the San Joaquin and the Sacramento Rivers. They reached their largest on the natural stream terrace that rose above the streambed. It is suggested that in the mid 1800s the woodlands were about a million acres of the Great Central Valley. Today they are estimated at about 102,000 acres, they have been greatly degraded and only 1% of what remains could be considered pristine.

Water-loving trees and shrubs make up the majority of the Riparian vegetation. Mule fat and quite a few species of willow are abundant. They are able to adapt to the patchy distribution of water. The trees of the woodlands were winter-deciduous that included Western Sycamore (Platanus racemosa), Box Elder (Acer negundo); Fremont Cottonwood (Populus fremontii); three species of willow. The most impressive is the Valley Oak (Quercus lobata); they have reached 27 feet in circumference. The Valley Oak and the Western Sycamore grow in the higher terraces. In the Nature Conservancy’s Cosumnes River Preserve is the largest stand of Valley Oak, it includes the Riparian Woodland and the endangered marshland.

The dropping of leaves in the winter goes to show that the stream environment is similar to that of the Eastern United States.

Some of the most endangered species are found in the Riparian Woodland, the California Hibiscus (Hibiscus californicus) is an ephemeral plant, white with a crimson center is one such plant.

 Animals of Riparian Woodlands

Among the most productive in the state that is able to support a large biomass of animals, most are visiting animals. The animals of the Riparian Woodlands, there are 39 species of mammals, 7 of lizards, 6 of snakes, 1 turtle, 69 of birds and an enormous number of insect species in the Sacramento Valley Riparian Woodlands.


Of the many the two worth mentioning are the Delta Green Ground Beetle (Elaphrus viridis) and the Valley Elderberry Longhorn Beetle (Desmocerus californicus dimorphus). The Valley Elderberry Longhorn Beetle is bright green and can be found in the vernal pools of Solano County, it is only known in the Riparian Woodlands of the Sacramento, Yolo and Merced Counties.

Of the 17 species of butterflies the largest and most common is the Western Tiger Swallowtail (Papilio rutulus). The Lorquin’s Admiral (Basilarchia lorquini), dark with white bands on its wings and orange tips when mature feed on leaves as larvae. The Mourning Cloak (Nymphalis antiopa) hibernate in the winter, they feed on willows by streams or on elms. The Satyr Anglewing (Polygonia satyrus), orange with brown spots, larvae feed on Creek Nettle.


The Western Yellow-billed Cuckoo (Coccyzus americanus), the barometer of the Riparian Woodlands is in declines, some attribute this to the use of DDT and other pesticides. This bird is grayish brown above and white below, wing tips are reddish and the underside of the tail is banded with black and white. There are probably 9-10 pairs in the Riparian Woodland along the southern fork of the Kern River.

The Yellow-breasted Chat (Icteria virens), the largest of California’s wood warblers it is also in decline. This bird is olive green on the back and bright yellow on its breast, from its bill to its eye is a black and white stripe the eye is ringed with white. This bird is only a summer visitor to the Woodland. A more common visitor is the Northern Mockingbird (Mimus polyglottos).

Tree nesting duck such as Wood Ducks (Aix sponsa), the Common Merganser (Mergus merganser), the Red-breasted Merganser (Mergus serrator) and the Hooded Merganser (Lophoduytes cucullatus) are also in decline in the Riparian Woodlands. Wood Ducks used to range up to the northern part of the state, now they are no longer common in the Great Central Valley. They tend to nest in hallow trees. Mergansers feed on fish they too have declined.

Disappearance of Native Vegetation

The beginning of the vegetation decline in the Great Central Valley dates back to the 1700s. 230 million acres of California prairies, its disappearance is attributed to overgrazing by domestic animals. This started with the Spanish introducing small, long-horned cattle and small, long-legged sheep know as Churro. At the height of the Spanish missions there were 400,000 herd of cattle and 300,000 sheep. The drought between 1828 and 1830 promoted additional over grazing and there was no water for plant regeneration. More livestock was introduced in the late 1840s when the 49ers came for the Gold Rush, there were approximately 3 million cattle and 9 million sheep by 1862. Heavy precipitation caused a lake to form over the prairie and drown livestock, followed by a two year drought plus over grazing lead to a dust bowl. Once normal precipitation resumed in the winter of 1864-1865 the livestock number had been greatly reduced.

Cattle declined to half-million by 1870 and sheep population increased. Sheep required less water and were easy to herd. Sheep herds were commonly herded into the Sierra Nevada pastures, during summer months. By 1875 there were an estimated 5.5 million sheep and the rangeland of the Great Central Valley was irreversibly damaged.

Introduced grasslands originated from introduced livestock from Mediterranean origin. The seeds came in on the coats and in the digestive tracks of animals. This has been recorded by the scientific study and identification of the grasses used in adobe brick building that the Spanish and early settlers built. In this way we know what grasses are original and which are introduced.

Herbaceous plants were also introduced, for example, sow thistles. Various members of the geranium family, Red Stem filaree and Storksbill, were also introduced. The missions were responsible for introducing members of the mustard family. Broccoli, cabbage, cauliflower, brussel sprouts, kale, kohlrabi, wild radish, and turnips were also introduced and members of the mustard family. Horehound is an introduced member of the mint family. Horehounds are used medicinally.

In the 1800’s land from Fresno to Chico was used to dry farm wheat. Dry farming relies on precipitation. Dry farming was typical the late 1920’s. Most of California’s’ agriculture industry is concentrated in the GCV. Four farm products generate Forty two percent of all California’s agricultural income. Starting in the 1980s dairy topped the list with beef, grapes, rice, and cotton. Half of the forty two percent is attributed to beef and dairy. Thirty percent of Ca. agriculture is identified as cash crops. This is a crop that is not required, a luxury item.

The GCV shows signs of poor ag. practices. Agriculture has encouraged gully (arroyo) formations, dirt blows off the land, soil erosion, and salt build up are other signs. A 1985 report from the American Farmland Trust states that about one third of Ca. 31 million acres of crop and rangeland suffers from excessive soil erosion. Another report stated that in 2000, over one third of the states’ 35 million acres of farmland will be destroyed by salt. 44,000 acres are eaten by urbanization.

The ground water is being over drafted by 1.5 million acre-feet per year. This causes the water tables to drop, promoting draining of wetlands, drying of springs, and subsidence. Marshes and Riparian Woodlands have suffered from this dewatering. Some parts of San Joaquin Valley have dropped as much as 30 ft.

Irrigation of big tracts of land, using water subsidized by public funds has helped large agribusiness to lean towards immediate profit. In 1981 eight companies, three of which were oil companies, managed two thirds of the state-irrigated land in the San Joaquin Valley. Heavy use of chemical fertilizers, herbicides, and pesticides brings high productivity for a short time. DDT and dieldrin have accumulated as leech water in the ground water. This concentration accumulates in the roots of plants. There was a plan to get rid of this toxic water into the San Francisco Bay. The incident at Keterson Wildlife Refuge happened and people realized the intensity of the problem.

Desertification is a term used to describe when land becomes desert like because of humans activities. Desertification is happening in the GCV. The symptoms are: salty soil, erosion, gully formation, subsidence, and replacement of native vegetation by weeds. The causes are overgrazing, poor agricultural practices, ground water overdraft, and poor water management. If environmentally sound actions are not taken soon, California will turn into a desert wasteland much like the Fertile Crescent in the Tigris and the Euphrates valleys. They were once the richest ag. region in the world and are now salty wastelands. (from Schoenherr, pages 516-543)


By: The Mama's and Papa's

Great Central Valley, also referred as the Central Valley or the Great

Valley, is an elongate depression that lies between the Coast Ranges and the

Sierra Nevada. It is about 430 miles long and about 75 miles wide.

Great Central Valley is actually 2 large valleys lying end to end, each

drained by a major river. North of San Francisco Bay the Sacramento Valley

is drained by the Sacramento River. San Joaquin Valley is drained by the

San Joaquin River. Flowing together these rivers were a formerly a massive

wetland /now one important Ag areas Calif.


Many biological communities such as Valley Grassland, Foothill Woodland or

Oak Woodland make ill regular boundaries of the Great Valley.


This geomorphic province more than any other has been altered by humans. In

unspoiled state contained 3 communities of plants and animals.

1. Valley Grassland.

2. Freshwater Marsh.

3. Riparian Woodland.


Great Central Valley is arid regions and share many characteristics of

desert provinces such as Saltbush Scrub and Alkali Sink in the low-lying

area of southern San Joaquin.




Climate of the Great Central Valley promotes widespread grasslands.

Precipitation occurs in the winter months but is reduced because of Coast

Ranges. Sacramento Valley precipitation is moderate. South valley is reduced

to desert proportions.


Cold-air drainage from the surrounding mountains becomes trapped, forming a

persistent inversion layer in the Central Valley resulting in tule fog.



Central Valley is a huge basin filled with sediments. Sands and gravels over

30,000 feet deep lie upon Sierran basement rocks tat extend downward at an

angle from the western slope of the Sierra Nevada.


Deepest part of the gravels and sands are marine sediments that have

accumulated since the late Jurassic time about 145 million years ago.

Apparently same time the sea retreated from valley at about the same time

southern Coast Ranges were uplifted with the basement rock continuing to



Last 5 million years sediments accumulated as alluvial deposits washed out

of the mountains.


Only topographical relief in Central valley is the Sutter Buttes.


Trapped beneath sediments of the San Joaquin Valley are rich oil fields/

Valley crude oil is very thick resulting in high-cost, low price product.




Valley Grassland: once covered all well drained areas in the Central Valley

as well as large valleys in the Coast Ranges and cismontane southern Calif.

Only 1% considered unspoiled today.


Benchgrasses grow upright in dense turfs in dense tufts of stems that arise

from a perennial root crown. With onset of winter rains these grasses

produce new growth with most growth during warmer spring months (April to



Pristine grasslands also contained annual grasses and herbs although the

annual grasses were not abundant as the perennial forms.


Wildflowers with numerous annual species and geophytes, perennials that

return each year from bulbs.



Vernal pools or "hog wallows" occur where the hardpan is close to the

surface. There are 3 kinds of pools in the Central Valley.

1. Valley pools /most common in low places of San Joaquin Valley in

basins or valleys

2. Pools of volcanic areas.

3. Terrace pools.


Widespread plant in vernal pool is a spore-bearing plant known as Quillwort

or Merlin's grass.


Pools of volcanic areas are found throughout the state; typified by those on

the Vina Plains in Tehama County and Mesa de Colorado in Riverside County /

floristically similar to terrace pools.


Terrace Pools occur on the some of the oldest soils in the state: ancient

flood terraces on higher ground. Water accumulates during winter months

because it is unable to percolate into the ground. Wildflowers bloom

according to the water level of the pool. Towards the center of the pools

soil become more alkaline thus favoring special plants. Endemism is high in

these ecological islands.


Vernal pool vegetation attains it highest development on terrace soils of

east side of the Central Valley.




Enormous marshes occurred where runoff from the mountains accumulated and

were habitat for many animals and plants when the conditions were pristine.


Wetlands habitats are characterized by a mixture of water and emergent

vegetation are known variously as swamps, marshes and bog.


Freshwater marshes typically occur in flatlands where water accumulates in

shallow low depression and are no longer common in Calif.


Calif virgin landscape consisted on 3 large lakes in the Central Valley

1.Tulare Lake 2.Buena Vista Lake and Kern Lake with bordering marshes and

sloughs. All 3 were a result of the runoff from the Sierra Nevada with and

estimated shoreline of marsh habitat of over 2100 miles.


Tule Lake represented the largest freshwater lake west of the Mississippi

River covering over 700sg. miles.


Marsh vegetation is distributed in distinct bands. Ecological requirements

for each of the plant types are precise enough that they occur in

single-species clumps of zones that appear as band on the edge of the water



Freshwater marshes are dominated by reedlike plants that grow in

water-saturated soil. Essentially 4 groups.

1. Juncus and bulrushes.

2. Scirpus.

3. Cyperus and cattails.

4. Typha


Marsh ecosystems are known to be the most productive in the world


On higher ground in the marshes water-loving trees such as willows. Black

Willow is the most common willow in marshes in the San Joaquin Valley, Red

Willow and Pacific Willow are numerous as well.



High productivity means that a marsh is capable of supporting a large

biomass of consumers. Most Animals unable to feed on vegetative parts of

marsh plants so much of biomass ends up as that feed back into system

through decomposition.


Most noticeable animals in marshes are birds. Migratory species such as

swans, ducks, and shorebirds visit Central Valley wetlands/but have suffered

decline because of human activities.


Many mammals are attracted to water, particularly in hot dry places most not

truly marsh species with the exception of the Muskrat.



Extensive Riparian Woodlands in the state formerly occurred in the Central

Valley, often known as gallery forests.


Riparian Woodlands vegetation consists of water-loving shrubs and trees


Some of California's rarest most endangered trees are restricted to the

Riparian Woodland: example California Hibiscus




Riparian woodlands are among the most productive habits in the state,

capable of supporting a large biomass of with most animals visiting from

other habitats seeking food, water and shelter.


(Insects) numerous insects are associated with riparian Woodland with 2 on

the listed as threaten by the federal gov. 1. Delta Green Ground Beetle,

2.Valley Elderberry Longhorn Beetle.


(Birds) Western Yellow-billed Cuckoo has been described as barometer of

conditions in the riparian woodland. Many believe the decline of population

of many bird species is from the use of pesticides.



Demise of native vegetation dates back to Spanish Mission and resulted

because of livestock practices of overgrazing and the introduction of alien

plants believed to beneficial for livestock production.


Riparian vegetation has been compromised by the economics of agriculture.

I.e. dam building and use of firewood etc.



Unique reptiles inhabit the Riparian Woodland among them Blunt-nosed Leopard

Lizard that is associate of Alkali Sink, dry was and bunchgrass habitats.



Ducks geese and shorebirds once abounded in the Central Valley and other

birds such as grouse and quail were over hunted and introduced species like

the pheasant and Chucker create competition for native birds.


The Turkey Vulture with its keen smell has been trained to locate leaks in

gas lines



In the grassland they take cover in two ways either by burrowers or graze in

large herds.


Early accounts of the Central Valley paint a picture of large herds of Mule

Deer, Pronghorn (formerly was considered to be a member of the family of

Antilcapride/ is not a true antelope but is classified in the family that

includes African antelope (Bovidae) as well as domestic cattle, sheep and



Tule Elk and Mule Deer and Pronghorn all suffered great decline because of

hunting and agricultural practices.


Predators include Mountain Lions, Grizzly Bears Grey Wolves coyotes and

foxes are inhabitants the Central Valley

The Chickadees (pp. 516-543)





  • The Great Central Valley is a huge basin filled with sediments.
  • Sands and gravels over 30,000 feet deep lie upon Sierran basement rocks that extended downward from the estern slope of the Sierra Nevada.
  • The deepest region of sediments is off-center near the eastern edge of the Coast Ranges where a deep fault system lies.
  • A thrust fault zone occurs along the western edge of the valley.
  • The deepest parts of the gravels and sands are marine sediments that have accumulated since late Jurassic time, about 145 million years ago. Apparently, the sea retreated from the valley at about the same time that the southern Coast Ranges were uplifted.
  • During the last 5 million years, sediments accumulated as alluvial deposits washed out of the mountains.
  • Trapped beneath the San Joaquin Valley is one of California’s richest oil fields. Some estimates indicate that there may be 6 billion barrels more to be recovered. However, San Joaquin Valley crude oil is very thick, making it a high-cost, low-price product.

Native Vegetation

Valley Grassland

  • Valley Grassland once covered all well-drained areas in the Great Central Valley. Only 1% of the grassland today could be considered pristine. Even in its disturbed form, Valley Grassland is still one of California’s most common communities, covering over 22 million acres of land.
  • Pristine grassland was dominated by perennial bunchgrasses such as needlegrasses (Stipa spp.), triple-awned grasses (Aristida spp.), bluegrasses (Poa spp.), and rye grasses (Elymus spp.). By far the dominant species was Purple Needlegrass, Stipa pulchra.
  • Bunchgrasses grow upright in dense tufts of stems that arise from a perennial root crown. With the onset of winter rains, these grasses produce new growth. During winter, cool weather and persistent overcast inhibit growth and photosynthesis. Rapid growth, flowering, and maturity normally occur from April to June.
  • Pristine grassland also included annual grasses, herbs and wildflowers. Among wildflowers are numberous annual apecies and geophytes, perennials that returned each year from bulbs, like lily (Liliaceae) and amaryllis (Amaryllidaceae).
  • Other wildflowers include Lupines (lupinus spp.), California Poppies, Eschscholtzia californica and Purple Owl Clover, Orthocarpus purpurascens. Also included are various members of the sunflower family (Asteraceae) and thistles (Cirsium spp.)
  • Areas inhabited by Valley Grassland include: The Carrizo Plain, a flat valley west of Taft; The Temblor Range, a low range of hills uplifted along the San Andreas fault; and Corral Hollow, another valley of the inner Coast Ranges situated about 8 miles southwest of Tracy.
  • The Corral Hollow Ecological Reserve is a 99 acre site compsed of 30% Riparian Woodland and 70% grassland. It is home to a wide variety of amphibans and reptiles, including the California Red-legged Frog (Rana aurora draytoni), the Foothill Yellow-legged Frog (Rana boylei), and the Western Pond Turtle (Clemmys marmorata). Seven species of reptile reach their northernmost distribution in this area.
  • Corral Hollow also fatures serpentine soils and unique vegetation, such as Desert Olive (Forestiera neomexicana) and Iodine Bush (Allenrolfea occidentalis), and Honey Mesquite (Prosopis glandulosa). Of particular interest is the presence of a species in the borage family called Large Flowered Fiddleneck (Amsinckia grandiflora).
Vernal Pools
Freshwater Marsh
Riparian Woodland
 Disappearance of Native Vegetation
Go to Other Chapter Summaries!
Marilyn Cannon, Dec. 2, 2002