Contra Costa County
County
Images, from left to right: Contra Costa County courthouse, Mount Diablo's North Peak
Seal Coat of arms Wordmark
Interactive map of Contra Costa County
Location in the state of California
Country	United States
State	California
Region	San Francisco Bay Area
Incorporated	February 18, 1850[1]
Named for	"Opposite coast" (Spanish: Contra costa) of the San Francisco Bay
County seat	Martinez
Largest city	Concord (population and land area) Richmond (total area)
Government
• Type	Council–CAO
• Body	Board of Supervisors
• Chair	John Gioia
• Vice Chair	Federal D. Glover
• Board of Supervisors[2]	Supervisors John Gioia Candace Andersen Diane Burgis Ken Carlson Federal D. Glover
• County Administrator Office[3]	Monica Nino
Area
• Total	804 sq mi (2,080 km2)
• Land	715.94 sq mi (1,854.3 km2)
• Water	81 sq mi (210 km2)
Highest elevation [4]	3,852 ft (1,174 m)
Population  (2020)
• Total	1,165,927
• Density	1,629/sq mi (629/km2)
Gross Domestic Product [5]
• Total	US$76.341 billion (2022)
Time zone	UTC−8 (Pacific Time Zone)
• Summer (DST)	UTC−7 (Pacific Daylight Time)
Area code	510, 341, 925
FIPS code	06-013
GNIS feature ID	1675903
Congressional districts	8th, 9th, 10th
Website	contracosta.ca.gov

Contra Costa County (/ˌkɒntrə ˈkɒstə/ ^ⓘ; Contra Costa, Spanish for 'Opposite Coast') is a county located in the U.S. state of California, in the East Bay of the San Francisco Bay Area. As of the 2020 United States Census, the population was 1,165,927.^[6] The county seat is Martinez.^[7][8] It occupies the northern portion of the East Bay region of the San Francisco Bay Area and is primarily suburban. The county's name refers to its position on the other side of the bay from San Francisco.^[9] Contra Costa County is included in the San Francisco–Oakland–Berkeley, CA Metropolitan Statistical Area.

History

Pre-human

In prehistoric times, particularly the Miocene epoch, portions of the landforms now in the area (then marshy and grassy savanna) were populated by a wide range of now extinct mammals, known in modern times by the fossil remains excavated in the southern part of the county. In the northern part of the county, significant coal and sand deposits were formed in even earlier geologic eras. Other areas of the county have ridges exposing ancient but intact (not fossilized) seashells, embedded in sandstone layers alternating with limestone. Layers of volcanic ash ejected from geologically recent but now extinct volcanoes, compacted and now tilted by compressive forces, may be seen at the site of some road excavations. This county is an agglomeration of several distinct geologic terranes, as is most of the greater San Francisco Bay Area, which is one of the most geologically complex regions in the world. The great local mountain Mount Diablo has been formed and continues to be elevated by compressive forces resulting from the action of plate tectonics and at its upper reaches presents ancient seabed rocks scraped from distant oceanic sedimentation locations and accumulated and lifted by these great forces. Younger deposits at middle altitudes include pillow lavas, the product of undersea volcanic eruptions.

Native American period

There is an extensive but little-recorded human history of pre-European settlement in this area, with the present county containing portions of regions populated by a number of Native American tribes. The earliest definitively established occupation by modern man (Homo sapiens) appears to have occurred six to ten thousand years ago. However, there may have been human presence far earlier, at least as far as non–settling populations are concerned. The known settled populations were hunter-gatherer societies that had no knowledge of metals and that produced utilitarian crafts for everyday use (especially woven reed baskets) of the highest quality and with graphic embellishments of great aesthetic appeal. Extensive trading from tribe to tribe transferred exotic materials such as obsidian (useful for the making of arrowheads and other stone tools) throughout the region from far distant Californian tribes. Unlike the nomadic Native American of the Great Plains it appears that these tribes did not incorporate warfare into their culture but were instead generally cooperative. Within these cultures the concept of individual or collective land ownership was nonexistent. Early European settlers in the region, however, did not record much about the culture of the natives. Most of what is known culturally comes from preserved contemporaneous and excavated artifacts and from inter-generational knowledge passed down through northerly outlying tribes of the larger region.

Spanish colonial

Early interaction of these Native Americans with Europeans came with the Spanish colonization via the establishment of missions in this area, with the missions in San Jose, Sonoma, and San Francisco and particularly the establishment of a Presidio (a military establishment) in 1776. Although there were no missions established within this county, Spanish influence here was direct and extensive, through the establishment of land grants from the King of Spain to favored settlers.

Mexican land grants

In 1821 Mexico gained independence from Spain. While little changed in ranchero life, the Mexican War of Independence resulted in the secularization of the missions with the re-distribution of their lands, and a new system of land grants under the Mexican Federal Law of 1824. Mission lands extended throughout the Bay Area, including portions of Contra Costa County. Between 1836 and 1846, during the era when California was a province of independent Mexico, the following 15 land grants were made in Contra Costa County.^[10]

The smallest unit was one square league, or about seven square miles, or 4,400 acres (17.8 square kilometers), maximum to one individual was eleven leagues, or 48,400 acres (195.9 km²), including no more than 4,428 acres (17.9 km²) of irrigable land. Rough surveying was based on a map, or diseño, measured by streams, shorelines, and/or horseman who marked it with rope and stakes. Lands outside rancho grants were designated el sobrante, as in surplus or excess, and considered common lands. The law required the construction of a house within a year. Fences were not required and were forbidden where they might interfere with roads or trails. Locally a large family required roughly 2000 head of cattle and two square leagues of land (fourteen square miles) to live comfortably. Foreign entrepreneurs came to the area to provide goods that Mexico could not, and trading ships were taxed.^{[note 1]}

• Rancho Cañada de los Vaqueros was granted to Francisco Alviso, Antonio Higuera, and Manuel Miranda (26,660 acres (107.9 km²) confirmed in 1889 to heirs of Robert Livermore).
• Two ranchos, both called Rancho San Ramon, were granted by the Mexican government in the San Ramon Valley. In 1833, Bartolomé Pacheco (southern San Ramon Valley) and Mariano Castro (northern San Ramon Valley) shared the two square league Rancho San Ramon. José María Amador was granted a four square league Rancho San Ramon in 1834.
• In 1834 Rancho Monte del Diablo (present day Concord, California) was confirmed with 17,921 acres (72.5 km²) to Salvio Pacheco (born July 15, 1793, died 1876). The Pacheco family settled at the Rancho in 1846 (between the Pacheco shipping port townsite and Clayton area, and including much of Lime Ridge). The boundary lines were designated with stone markers. Clayton was later located on El Sobrante's lands just east of Rancho Monte del Diablo (Mount Diablo).
• In 1834, Rancho Arroyo de Las Nueces y Bolbones, aka Rancho San Miguel (present day Walnut Creek), was granted to Juana Sanchez de Pacheco, in recognition of the service of Corporal Miguel Pacheco 37 years earlier (confirmed 1853, patented to heirs 1866); the grant was for two leagues, but drawn free hand on the diseño/map, and reading "two leagues, more or less" as indicated in the diseño, but actually including and confirmed for nearly four leagues or nearly 18,000 acres (72.8 km²), but only 10,000 acres (40.5 km²) were ever shown as having once belonged to Juana Sanchez.
• 'Meganos' means 'sand dunes.' A "paraje que llaman los Méganos" 'place called the sand dunes' (with a variant spelling) is mentioned in Durán's diary on May 24, 1817. Two Los Meganos Ranchos were granted, later differentiated as Rancho Los Meganos (1835, three leagues or at least 13,285 acres (53.8 km²)) in what is now the Brentwood area, to Jose Noriega then acquired by John Marsh; and Rancho Los Medanos (to Jose Antonio Mesa and Jose Miguel Garcia, Pittsburg area, dated November 26, 1839).

Bear Flag Republic and statehood

The exclusive land ownership in California by the approximate 9,000^[11] Hispanics in California would soon end. John Marsh, owner of Rancho Los Meganos in Contra Costa County, had a lot to do with this. He sent letters to influential people in the eastern United States extolling the climate, soil, and potential for agriculture in California, with the deliberate purpose of encouraging Americans to immigrate to California and lead to its becoming part of the United States. He succeeded. His letters were published in newspapers throughout the East and started the first wagon trains rolling toward California. He also invited them to stay on his ranch until they could get settled, so the Rancho Los Meganos became the terminus of the California trail.^[12]

This led to the Bear Flag Revolt in 1846 when about 30 settlers originally from the United States declared a republic in June 1846 and were enlisted and fighting under the U.S. flag by July 1846. Following the Mexican–American War of 1846–48, California was controlled by U.S. settlers organized under the California Battalion and the U.S. Navy's Pacific Squadron. After some minor skirmishes, California was under U.S. control by January 1847 and formally annexed and paid for by the U.S. in 1848. By 1850, California's population of over 100,000 was rapidly growing due to the gold rush and the large amount of gold being exported east, which gave California enough clout to choose its own boundaries, write its own constitution, and be admitted to the Union as a free state in 1850 without going through territorial status as required for most other states.

In 1850 California had a non-Indian population of over 100,000.^[13] The number of Indians living in California in 1850 has been estimated to be from 60,000 to 100,000. By 1850 the Mission Indian populations had largely succumbed to disease and abuse and only numbered a few thousand. California's 1852 state Census gives 31,266 Indian residents, but this is an under-count since there was little incentive and much difficulty in getting it more correct.^[14] Zdroj:https://en.wikipedia.org?pojem=Contra_Costa_County,_California
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