The Orinda Formation is a
Miocene epoch
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...
geologic formation
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...
in the
Berkeley Hills
The Berkeley Hills are a range of the Pacific Coast Ranges that overlook the northeast side of the valley that encompasses San Francisco Bay. They were previously called the "Contra Costa Range/Hills" (from the original Spanish ''Sierra de la C ...
of the
East Bay
The East Bay is the eastern region of the San Francisco Bay Area and includes cities along the eastern shores of the San Francisco Bay and San Pablo Bay. The region has grown to include inland communities in Alameda and Contra Costa countie ...
region of the
San Francisco Bay Area
The San Francisco Bay Area, often referred to as simply the Bay Area, is a populous region surrounding the San Francisco, San Pablo, and Suisun Bay estuaries in Northern California. The Bay Area is defined by the Association of Bay Area Go ...
,
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
.
[USGS.gov: "Upper Cretaceous and Lower Tertiary Rocks Berkeley and San Leandro Hills, California"]
by J. E. Case, GEOLOGICAL SURVEY BULLETIN 1251-J, 1968.
It is found within
Alameda County
Alameda County ( ) is a List of counties in California, county located in the U.S. state of California. As of the 2020 United States Census, 2020 census, the population was 1,682,353, making it the 7th-most populous county in the state and List ...
and
Contra Costa County
) of the San Francisco Bay
, subdivision_type = Country
, subdivision_name = United States
, subdivision_type1 = State
, subdivision_name1 = California
, subdivision_type2 ...
.
[
]
Geology
The Orinda Formation is a coarse alluvial conglomerates sedimentary formation. It underlies the volcanic Moraga Formation.
It preserves fossils
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...
dating back to the Miocene epoch of the Neogene
The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...
period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
.
Geologic Hazards
The Orinda Formation is prone to landsliding due to intrinsic properties such as its weak cohesive strength and low friction angle. Landslides less than or equal to 10 acres in size occur as slides, slumps, and earthflows on dip or parallel to dip slopes. In the formation, landslides greater than or equal to 10 acres in size are common to very common and occur as slumps and slides on anti-dip slopes.
See also
*
* List of fossiliferous stratigraphic units in California
This article contains a list of fossil-bearing stratigraphic units in the state of California, California, U.S.
Sites
See also
* Paleontology in California
References
*
{{DEFAULTSORT:Fossiliferous stratigraphic units in California
F ...
* Paleontology in California
Paleontology in California refers to paleontologist research occurring within or conducted by people from the U.S. state of California. California contains rocks of almost every age from the Precambrian to the Recent. Precambrian fossils are pres ...
References
Berkeley Hills
Pliocene California
Geologic formations of California
Geology of Alameda County, California
Geology of Contra Costa County, California
Natural history of the California Coast Ranges
Natural history of the San Francisco Bay Area
Pliocene Series of North America
{{Neogene-stub