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Geodiversity Atlas—Golden Gate National Recreation Area, California


Geodiversity refers to the full range of herbal geologic (rocks, minerals, sediments, fossils, landforms, and bodily processes) and soil assets and approaches that take place in the park. A product of the Geologic Resources Inventory, the NPS Geodiversity Atlas supplies statistics in guide of education, Geoconservation, and built-in administration of residing (biotic) and non-living (abiotic) factors of the ecosystem.

Geologic Features and Processes

Plate Tectonic Setting Related

Rocks of the Franciscan Complex
Most of the basement rocks in the park belong to the Franciscan Complex. These rocks have been at first deposited in marine surroundings in a sequence established with basalt and greenstone, observed by way of chert and limestone, and in the end graywacke sandstone and shale. Subsequently, the rocks have been metamorphosed in a subduction area and accreted to the North American continent. Serpentinite (hydrothermally altered historic oceanic crust) and different hydrothermal and metamorphic rocks additionally take place in the Franciscan Complex.

Franciscan Terranes
The Franciscan Complex is divided into terranes that signify awesome episodes of accretion onto the North American continent. The terranes consist of blocks of Franciscan rocks in which the authentic depositional sequence is from time to time nonetheless visible.

Franciscan Mélange
Mélange are zones of “crushed up” and “mangled” Franciscan rocks that separate the specific terranes. Because mélange is so sheared, it is effortlessly eroded into rounded hills at some stage in the park. Franciscan mélange is regularly referred to as the “Central terrane.”

Rocks of the Salinian Complex
The Salinian complex is composed chiefly of the igneous rock granite. It originated from the equally big batholith that fashioned the core of the Peninsular Ranges and Sierra Nevada. A sliver of this complexity used to be carried north alongside the San Andreas Fault, and these days it types Montara Mountain and tons of the basement rocks in Point Reyes National Seashore.

Cenozoic Rocks and Deposits
Sedimentary rocks had been deposited in the park, mostly via surficial processes, at some point of the closing sixty six million years. During this time, tectonism in the San Francisco Bay Area advanced from a subduction to a seriously change regime; the rocks deposited at some stage in this time mirror this complicated transition. Tension, compression, and localized faulting related with the improvement of the San Andreas Fault broke the pre-Cenozoic bedrock into blocks which created basins and uplifts. Cenozoic rocks are especially conglomerate or sandstone and their depositional settings vary from marine to coastal to nonmarine.

Faults and the San Andreas Fault System
Nearly 390 km (240 mi) of faults are mapped in the park. The San Andreas Fault is the most universal however no longer the sole fault in the San Francisco Bay Area. In actuality, the San Andreas Fault is no longer a single fault, however a machine of many faults that accommodate seriously changing plate action between the Pacific and North American tectonic plates. Thrust faults, which separate terranes and zones of mélange, are additionally a frequent characteristic in the park. Thrust faults are accountable for bringing Franciscan rocks towards the surface; erosion is exposing these rocks today.

Earthquakes are ubiquitous in the San Francisco Bay Area. Most of the primary earthquakes in California are prompted via actions alongside faults of the San Andreas Fault system. Many of the faults in this gadget are seismically connected, which means that an earthquake alongside one may want to generate motion on another.

Related: Major Groups of Dinosaurs

Paleontological Resources

The park carries good sized paleontological sources from the stays of Cenozoic Era mammals to Mesozoic Era marine invertebrates, and the doable for persevered discovery is considerable. A paleontological useful resource stock for the park used to be executed in 2015.

All NPS fossil sources are blanketed below the Paleontological Resources Preservation Act of 2009 (Public Law 111-11, Title VI, Subtitle D; sixteen U.S.C. §§ 470aaa - 470aaa-11).

Surficial Geology Related

Landslide Deposits and Slope Movements
Four sorts of slope motion are frequent in the San Francisco Bay Area—rockfall, slumps, particle slides, and earth/debris flows—through others can and do occur. Slope moves take place principally in vulnerable rocks, such as mélange, serpentinite, and unconsolidated Quaternary deposits. Slope actions additionally appear on steep slopes, such as these alongside the coast. Heavy rain, earthquakes, and undercutting of steep slopes have brought about slope moves in the park.

Alluvium and Fluvial Processes
Dynamic fluvial systems, which includes rivers, streams, and creeks, have deposited alluvium in the park all through the final 2.6 million years (Quaternary Period). Recent alluvium is determined chiefly in energetic drainage channels and valleys. Older alluvial deposits supply perception to the records of improvement of the cutting-edge San Francisco watershed.

Coastal Features and Processes
The shoreline of the park includes cliffs and bluffs, seashores and dunes, and calm bays and estuaries. Distinctive tactics function in each environment, and each responds in another way to the effects of local weather alternate such as adjustments in sea stage and fees of erosion. Slope moves are frequent on coastal cliffs. Beaches and dunes trade measurement and form seasonally in response to wave strength and storms.

Sea Caves
Sea caves are a frequent characteristic alongside the coast of California. Sea caves shape the place waves and the sediments they elevate take advantage of and make bigger vulnerable zones (joints, fractures, and fissures) in in any other case erosion-resistant, cliff-forming rock. Sea caves are more frequent in the more difficult and older rocks of the Franciscan Complex than in the softer and youthful Cenozoic-age sedimentary rocks. The exact quantity of caves in the park is unknown, however the quantity is probably at least one hundred and doubtlessly greater than five hundred Due to accessibility challenges, a formal cave stock has now not but been completed.

All NPS cave sources are blanketed below the Federal Cave Resources Protection Act of 1988 (FCRPA)(16 U.S.C. § 4301 et seq.).

Abandoned Mineral Lands

According to the NPS servicewide deserted mineral lands database, Golden Gate National Recreation Area consists of 23 deserted mineral land points at 5 sites. The limestone quarry close to Mori Point used to be mined by way of the Spanish in the 1700s to grant whitewash for Presidio buildings.

NPS AML websites can be vital cultural assets and habitat, however many pose dangers to park site visitors and wildlife, and degrade water quality, park landscapes, and bodily and organic resources. Be protected close to AML sites—Stay Out and Stay Alive!

Geology Field Notes

Students and instructors of college-level (or AP) introductory geology or earth science instructing guides will discover that every park's Geologic Resource Inventory document consists of the Geologic History, Geologic Setting, and Geologic Features & Processes for the park which affords a beneficial precis of their average geologic story. See Maps and Reports, below.

Regional Geology

Golden Gate National Recreation Area is a section of the Pacific Border Physiographic Province and shares its geologic records and some attribute geologic formations with a location that extends nicely past park boundaries.