The Jalama Formation is a sedimentary

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

 rock formation widespread in southern Santa Barbara County, California. Of late Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 age, the unit consists predominantly of clay shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

 with some beds of sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

. A particularly erosion-resistant sandstone within the unit forms the scenic Nojoqui Falls

Nojoqui Falls

Nojoqui Falls is a seasonal waterfall in the Santa Barbara County, California park of the same name.- Description :From the sign posted near the falls: "Unlike most waterfalls, which gradually erode upstream, the Nojoqui Falls have built outward from the cliff over time...

 south of Solvang

Solvang, California

Solvang is a city in Santa Barbara County, California, United States. It is one of the communities that make up the Santa Ynez Valley. The population was 5,245 at the 2010 census, down from 5,332 at the 2000 census...

.

Type locality and description

The type locality

Type locality (geology)

Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....

 of the Jalama Formation is in southwestern Santa Barbara County on the low ridgeline between Santa Anita and Bulito Canyons, within Hollister Ranch

Hollister Ranch

The region presently known as the Hollister Ranch is defined by of fallow and fertile fields, mountains and valleys along the Pacific Ocean of California between Gaviota State Park and Point Conception. It was the site of some of the oldest known human settlements in the new world, the last...

, near the crest of the Santa Ynez Mountains

Santa Ynez Mountains

The Santa Ynez Mountains are a portion of the Transverse Ranges, part of the Pacific Coast Ranges of the west coast of North America, and are one of the northernmost mountain ranges in Southern California.-Geography:...

, and near the headwaters of Jalama Creek. The formation is found from this area eastward along the Santa Ynez range in periodic outcrops, underlying either the Anita Shale (in the western portion of its range) or the Juncal Shale (in the east). The largest outcrop in the Santa Ynez range is along the north slope of the mountains near Santa Ynez Peak, where it is exposed for approximately six miles. Other outcrops occur north of the Santa Ynez Fault, in the San Rafael Mountains along the Little Pine Syncline and along the Hildreth Fault.

Characteristic shale beds within the Jalama are dark gray to black, micaceous, and often carbonaceous

Carbonaceous

Carbonaceous is the defining attribute of a substance rich in carbon. Particularly, carbonaceous hydrocarbons are very unsaturated, high-molecular-weight hydrocarbons, having an elevated carbon:hydrogen ratio....

. Sandstones interbedded with the shales are arkosic, light gray to tan, and sometimes massive, as at the base of the type section on Hollister Ranch. Another interbedded unit occasionally encountered is a cobbly conglomerate, which outcrops on the north slope of the Santa Ynez Mountains south of Gibraltar Reservoir. The cobbles in this unit are detritus from a granitic source rock in a gray to brown matrix. The overall Jalama Formation varies in thickness from around 2,000 feet near the Romero Saddle north of Carpinteria, to about 4,000 feet at the type location more than forty miles to the west.

Deposition environment and geologic history

The region of present-day Santa Barbara and Ventura County during the late Cretaceous was submerged, and the depositional environment was one of a narrow shelf and submarine fans. The previously exposed Espada Formation, after a period of erosion, was now underwater, and began to receive layers of sediment which would become the Jalama Formation. Periodic episodes of deeper and shallower water resulted in finer and coarser sediments, respectively – shales versus sandstones. The crustal block on which the Jalama formation was deposited has been inferred to have rotated approximately 90 degrees clockwise and moved northward along the coast from its former position nearer San Diego. This motion took place beginning in the early Miocene

Miocene

The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...

, during a period of deformation along the boundaries of the Pacific

Pacific Plate

The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....

 and North American

North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

 Plates, a boundary represented today by the San Andreas Fault

San Andreas Fault

The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...

.

The unit lies unconformably on the Espada Formation

Espada Formation

The Espada Formation is a sedimentary rock formation widespread in Santa Barbara County, California. Of late Jurassic to Cretaceous age, the unit consists primarily of shale with some interbedded thin layers of sandstone, conglomerate, and limestone....

, also of Cretaceous age, and in places on the older Franciscan Formation

Franciscan Assemblage

The Franciscan Assemblage is a geological term for an accreted terrane of heterogeneous rocks found on and near the San Francisco Peninsula. It was named by geologist Andrew Lawson who also named the San Andreas Fault which bounds the Franciscan Assemblage....

, which is probably of Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 age. In one location, in Nojoqui Canyon near the Nojoqui Falls, the Jalama is in conformable contact with the underlying Espada, indicating one area that remained submerged through the era.

The Jalama formation is separated by overlying sedimentary layers by an unconformity most everywhere it has been found, as the Paleocene

Paleocene

The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

 is unrepresented in the fossil record in southern Santa Barbara County, and the stratigraphic sequence goes directly from the Cretaceous Jalama to Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 units, including the Anita and Juncal Formations. In his 1966 book on the geology of the central Santa Ynez Mountains, Dibblee finds the Cretaceous Jalama Formation to be in conformable contact with the Eocene Juncal in the eastern part of the Santa Ynez range, without mentioning the intervening Paleocene; in this portion of the unit there are no fossils to provide clues as to date.

Paleontology

While the eastern part of the Jalama Formation is almost without fossils, some localities in the western part are richly fossiliferous, and at least one species – Lysis jalamaca, from an extinct genus of shallow-marine gastropod – has been named for the unit. Lysus jalamaca has been dated to between 70-75 million years before present, in the late Cretaceous.

Other fossils found in the Jalama formation, listed in Dibblee's 1950 book include six species of bivalves and one species each of gastropod and cephalopod. All of these are described as "abundant", with numerous others not listed; all are indicative of upper Cretaceous.