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37-517: The village of Timigtac was located around the present-day Rockaway Beach area, near Mori Point . A large shellmound in the area indicates the region was long inhabited by the Aramai of the Ramaytush Ohlone . The inhabitants of Timigtac and another nearby village Pruristac actively quarried limestone from the mountain for trade, construction, and decoration. Timigtac and Pruristac were

74-455: A complete section of oceanic crust has not yet been drilled, geologists have several pieces of evidence that help them understand the ocean floor. Estimations of composition are based on analyses of ophiolites (sections of oceanic crust that are thrust onto and preserved on the continents), comparisons of the seismic structure of the oceanic crust with laboratory determinations of seismic velocities in known rock types, and samples recovered from

111-407: A density of about 2.7 grams per cubic centimeter. The crust uppermost is the result of the cooling of magma derived from mantle material below the plate. The magma is injected into the spreading center, which consists mainly of a partly solidified crystal mush derived from earlier injections, forming magma lenses that are the source of the sheeted dikes that feed the overlying pillow lavas. As

148-454: A profitable sand dredging business on the quarry's backside. Ideal Cement took over the quarry operation after that time and owned it until 1971; later operators were Rhodes and Jamison and Quarry Products . The quarry ceased operation in 1987, and is currently (2019) being stabilized and restored. The coastal bluffs have verticality as steep as 60 percent, while some of the quarry surfaces are completely sheer. The limestone beds within

185-471: A referendum called Measure L. The property was sold in 2009, and in 2016, Pacifica voters again rejected a development which would have included an office and retail building, 206-unit apartment complex, 188-room hotel, 13,000 square foot conference center, and 12-unit hotel bungalow complex. Rockaway Beach, Pacifica, California Rockaway Beach is a shoreline area of the Pacific Ocean in

222-749: A role in local history since the arrival of the Portola Expedition , the Spanish explorers credited with discovery of the San Francisco Bay . As early as 1776, limestone quarried in the Rockaway Quarry lime pits was used to whitewash the newly built Presidio of San Francisco . More recent investigations suggest that early settlements in San Pedro Valley also used this limestone for their foundations. In 1907,

259-410: Is continuously being created at mid-ocean ridges. As continental plates diverge at these ridges, magma rises into the upper mantle and crust. As the continental plates move away from the ridge, the newly formed rocks cool and start to erode with sediment gradually building up on top of them. The youngest oceanic rocks are at the oceanic ridges, and they get progressively older away from the ridges. As

296-449: Is in the west Pacific and north-west Atlantic  — both are about up to 180-200 million years old. However, parts of the eastern Mediterranean Sea could be remnants of the much older Tethys Ocean , at about 270 and up to 340 million years old. The oceanic crust displays a pattern of magnetic lines, parallel to the ocean ridges, frozen in the basalt . A symmetrical pattern of positive and negative magnetic lines emanates from

333-586: Is known to exist on the Mori Point National Park property immediately adjacent to the north. Hugging the coast at the center of Rockaway Beach is a cluster of restaurants and shops, the oldest of which is a Pacifica landmark, Nick's Seafood Restaurant. Another restaurant, historically the romantic Moonraker, hosts nighttime views over the illuminated waves of the Pacific crashing at the restaurant foundation bulwarks. Newer shops nestle behind

370-535: Is sparse on the beach with occurrences of succulent sea fig , Hottentot fig , and fat hen in the sandy areas. Farther away from the beach there are California poppies , sand verbena , and bush lupines . The near littoral elevation gradually increases toward the north until it reaches a headland peak of 175 feet. Habitat on the headland east-facing slope consists of northern coastal scrub , considerable prostrate coyote brush , bush monkey flower , and colonies of bush lupine. A gamut of coastal wildflowers inhabit

407-556: The Azores and Iceland . Prior to the Neoproterozoic Era 1000 Ma ago the world's oceanic crust was more mafic than present-days'. The more mafic nature of the crust meant that higher amounts of water molecules ( OH ) could be stored the altered parts of the crust. At subduction zones this mafic crust was prone to metamorphose into greenschist instead of blueschist at ordinary blueschist facies . Oceanic crust

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444-537: The California Coastal Commission and the City of Pacifica would be needed for any reclamation project. There have been multiple efforts over the years to develop the abandoned quarry. In the late-1990s, housing and a convention center were proposed but blocked by local environmental groups. In 2005, a 355 residential units project, a luxury hotel and retail space were voted down by Pacificans in

481-602: The Mexican–American War , the Rockaway Quarry was sold and quarrying declined. In 1906, however, the dual requirements of Ocean Shore Railroad construction and the 1906 earthquake resulted in the reopening of the Rockaway Quarry in 1907, due to it being one of the few areas in the San Francisco area where limestone was available in industrial quantities. The quarry provided ballast and the trackbed of

518-557: The Moonraker, many a product of the city's 1986 redevelopment plan. 37°36′36″N 122°29′51″W  /  37.61000°N 122.49750°W  / 37.61000; -122.49750 Oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates . It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust , composed of troctolite , gabbro and ultramafic cumulates . The crust overlies

555-489: The Permanente terrane, which was carried to the ocean's edge through earthquakes over a period of 25 million years. Geochemical studies of Calera limestone show that fragments of the rock may be dismembered oceanic crust . In January 2023, a reclamation plan was proposed for the Rockaway Quarry site. The plan focused on grading the uneven slopes, replanting native vegetation, and creating a wetlands area. Approval from

592-622: The Rockaway Beach quarry was established as a continuously-operating commercial entity known as the Stone Brothers. After construction of the Ocean Shore Railroad in 1907, limestone from this quarry was conveyed to assist with the rebuilding of San Francisco after the 1906 San Francisco earthquake . Quarry materials were actually used as ballast for the trackbed of the railroad; moreover, after completion of

629-623: The area, and portions of the property were converted into a wastewater treatment plant in 2000. The area lies between the Pilarcitos Fault , the San Andreas Fault , and the San Gregorio Fault . Geologists have dated fossils at the site as between 88 and 105 million years old – in the middle of the long Cretaceous Period . Calera limestone found at Rockaway Quarry is part of a group of Franciscan rocks called

666-403: The developed area from marine erosion . Near Calera creek there is aquatic vegetation including rushes , bulrushes , horsetail , fat hen , and plantain . The quarry area hosts a surprising number of amphibians, reptiles, small mammals, and a variety of birds. Avafauna sighted here include herons , egrets , California least terns , and red-winged blackbirds . The headland cliffs within

703-418: The headland slopes; in addition to California poppy, there are goldenasters , Douglas iris , and many other native species. The steep bluff faces host plants that are tolerant of wind and sea salt mist, such as silver beachweed , sea rocket , and extensive patches of yarrow . North of the developed area of Rockaway Beach is a hidden quarry , whose habitat is severely disturbed. Rip-rap boulders protect

740-412: The lavas cool they are, in most instances, modified chemically by seawater. These eruptions occur mostly at mid-ocean ridges, but also at scattered hotspots, and also in rare but powerful occurrences known as flood basalt eruptions. But most magma crystallises at depth, within the lower oceanic crust . There, newly intruded magma can mix and react with pre-existing crystal mush and rocks. Although

777-406: The mantle rises it cools and melts, as the pressure decreases and it crosses the solidus . The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness (7±1 km). Very slow spreading ridges (<1 cm·yr half-rate) produce thinner crust (4–5 km thick) as the mantle has a chance to cool on upwelling and so it crosses

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814-438: The mid-oceanic ridge basalts, which are derived from low- potassium tholeiitic magmas . These rocks have low concentrations of large ion lithophile elements (LILE), light rare earth elements (LREE), volatile elements and other highly incompatible elements . There can be found basalts enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands ,

851-503: The north and west sides of Mori Point by the 1950s. The Quarry was sold in 1953, and leased to Howard Marks from 1953 to 1968, to Rhodes & Jamieson from 1968 to 1975, and then to the last commercial operations, Quarry Products Incorporated, from 1975 until its closure in 1987. When commercial quarrying ended, much of the area was left in degraded condition with unstable slopes, bare rocky bluffs, and soil vulnerable to invasive vegetation. Non-native species are still commonly found around

888-413: The ocean floor by submersibles , dredging (especially from ridge crests and fracture zones ) and drilling. Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. According to mineral physics experiments, at lower mantle pressures, oceanic crust becomes denser than the surrounding mantle. The most voluminous volcanic rocks of the ocean floor are

925-508: The oceanic crust can be used to estimate the (thermal) thickness of the lithosphere, where young oceanic crust has not had enough time to cool the mantle beneath it, while older oceanic crust has thicker mantle lithosphere beneath it. The oceanic lithosphere subducts at what are known as convergent boundaries . These boundaries can exist between oceanic lithosphere on one plate and oceanic lithosphere on another, or between oceanic lithosphere on one plate and continental lithosphere on another. In

962-592: The only Ohlone villages between Montara Mountain and the Golden Gate due to strong coastal winds and sandy soil . Spanish colonization of San Francisco began in 1769 with the first European sighting of the San Francisco Bay . By 1776, Spanish settlers employed Indian labor to quarry limestone from the Rockaway Quarry to build the San Francisco Presidio and mission buildings. The lime pits were also used to make whitewash . In this period,

999-401: The quarry are hard and fresh, with close- and widely-spaced fractures. Some of these beds are underlain by greenstone , an altered volcanic rock that becomes less weathered with depth. The eastern portion of the quarry area is underlain by alluvial terrace deposits. The beach littoral zone is underlain by Holocene age beach sand and the upper sands vary in depth by season, depending on

1036-659: The quarry provide nesting sites for bank swallows , pelagic cormorants , and Brandt's cormorants . Three endangered species are found proximate to Rockaway Beach: the San Francisco garter snake , the San Bruno elfin butterfly , and the California red-legged frog . These last two are found within the quarry property; the California red-legged frog is a critical food source for the San Francisco garter snake that

1073-593: The quarry was under the control of the Franciscan padres at Mission San Francisco de Asís . After Mexican Independence and secularization , present-day Pacifica was granted to the mayor of San Francisco and Commandant of the Presidio , Francisco Sánchez , as the Rancho San Pedro . Sánchez used the Rockaway Quarry to produce whitewash for his adobe home , which was completed in 1846. Following

1110-422: The railroad, Rockaway Beach was considered a suburb of San Francisco due to convenient access. This all changed after legal problems resulting from landslide repair caused the railroad to go bankrupt in 1921. Highway 1 was completed from Montara to Rockaway Beach in 1937, thereby reopening the local area again to easy northern access. Horace Hill operated the quarry from the early 1940s to 1953, along with

1147-594: The railroad, and building material to rebuild the city. The quarry's operators were E.B. and A.L. Stone, who leased the quarry from the Tobin family of San Francisco. In 1942, the Tobin family transferred ownership to Hibernia Bank . Horace Hill then bought it and established Rockaway Quarry, Incorporated, producing concrete aggregate, ballast, and high-grade limestone during World War II . Other companies began limestone production around Rockaway Beach , and pits appeared on

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1184-453: The rigid uppermost layer of the mantle . The crust and the rigid upper mantle layer together constitute oceanic lithosphere . Oceanic crust is primarily composed of mafic rocks, or sima , which is rich in iron and magnesium. It is thinner than continental crust , or sial , generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has

1221-485: The second situation, the oceanic lithosphere always subducts because the continental lithosphere is less dense. The subduction process consumes older oceanic lithosphere, so oceanic crust is seldom more than 200 million years old. The process of super-continent formation and destruction via repeated cycles of creation and destruction of oceanic crust is known as the Wilson Cycle . The oldest large-scale oceanic crust

1258-538: The solidus and melts at lesser depth, thereby producing less melt and thinner crust. An example of this is the Gakkel Ridge under the Arctic Ocean . Thicker than average crust is found above plumes as the mantle is hotter and hence it crosses the solidus and melts at a greater depth, creating more melt and a thicker crust. An example of this is Iceland which has crust of thickness ~20 km. The age of

1295-405: The southern portion of Pacifica, California , United States, approximately 7 miles (11 km) south of the city of San Francisco . It is located within a gently curving embayment with direct access via Rockaway Beach Avenue and providing easy access to Highway 1 . The beach itself is a popular place to visit with many restaurant and shopping venues although erosion has decreased its size over

1332-454: The surf scouring of beach sands in the winter and the gradual rebuilding of sands in the summer. The beach and headlands are mostly California coastal prairie and northern coastal scrub , while the riparian area of Calera Creek presents the most important upland habitat of the area. Although the beach and headlands area are the least disturbed natural areas of the Rockaway Beach area, they are used moderately as recreation spots. Vegetation

1369-561: The years. It is noted for its scenic overlook , and is one of the cleanest beaches in the San Francisco Bay Area . There are no known prehistoric remains in Rockaway Beach itself; however, the site of the Ohlone Native American village site of Timigtac is located about a half mile away on Calera Creek , immediately to the east of Rockaway Beach by State Route 1. The Rockaway beach area has played

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