Geology

How is Geology Used in Forest Management?

Application of Geologic Principles helps:

• In locating Threatened or Endangered species of plants and animals
• Determine the potential for locating valuable minerals
• In finding suitable locations to drill for groundwater
• Define appropriate land uses in different geomorphic terrains
• In assessing the risk of landsliding
• In the location of trails and roads
• Define the foundation conditions for bridges and retaining walls
• Define how to construct stable, low maintenance drainage systems for roads and excavated areas
• Determine ecosystem patterns and associations between geologic/geomorphic units and flora, fauna, soils, water, etc.
• Teach students of all ages facts about the earth and its influence on components of the ecosystem

Engineering Geology, Geomorphology, Hydrogeology, Paleontology, Mineralogy, Geologic Mapping, Economic Geology, Seismology, Mining Engineering and Petroleum Geology are all important branches of the geological sciences that are applied to many aspects of forest management including:.

• Road and trail building and reconstruction
• Landslide analysis and mitigation
• Groundwater management and development
• Burn area rehabilitation
• Location of habitat for T&E species
• Mining administration
• Mine and landfill reclamation
• Oil and gas administration
• Fossil and cave management
• Geologic special interest area interpretation
• Environmental education
• Land management planning
• Watershed restoration, etc.

A fault is a break in the earth's crust along which movement occurs: rock on one side of a fault moves in relation to that on the other side. Faults result when stresses within the earth, cause deformation in the upper part of the earth's crust.

Earthquakes occur when a sudden motion or slip occurs along a preexisting fault, or when stresses create a rupture causing a new fault to form.

The size of a quake that we feel on the earth's surface depends upon a number of things including: the magnitude of stress along the fault, the amount of time the stress has had to build up), the depth to the origin of the fault motion, and the type of bedrock in and around the fault zone. Certain rock types are more resistant to fault slip, so they slip less frequently, building up pressure under the tectonic stress. Then, when the actual displacement event does occur, all the built up pressure is released in a very strong earthquake. Other rock types, particularly those containing the mineral, serpentine, are not resistant to fault slip, and so motion occurs continuously and gradually; stress does not build up to cause significant earthquakes. The most famous and significant fault in California, the San Andres runs the northern portion of the Forest, which lays on serpentine rich bedrock. This explains why major earthquakes are rare in and around the Los Padres National Forest when compared to other sections of the San Andreas nearer to Los Angeles and San Francisco. Besides the San Andreas, the Los Padres is laced with hundreds of faults, some very old and inactive, some continuously active. Many of these faults run parallel with either the Transverse Ranges, which run east-west or the Coast Ranges, which run northwest-southeast.

View a US Geological Survey (USGS) map of California showing recent earthquake activity.

The US Forest Service takes geologic hazards, including seismic activity and slope instability into account when managing forest land, and its resources and facilities. Landslides have damaged sections of Los Padres roads multiple times in the past, and seismic activity along the numerous active faults that run through Los Padres National Forest also has significant potential to damage roads and other human-made structures. Rapid erosion of topsoil after forest fires can be devastating to fish populations and severely slow the re-vegetation of burn-areas. Detailed maps of both bedrock geology and geologic hazard potential are used in the planning process for Forest Service projects to reduce or eliminate their geohazard potential. However, ongoing work is needed to locate and understand the mechanics of slope failure, and to protect human life and property.

Landslides occur when the earth responds to one or more of the following situations: seismic shaking; saturation of soil on a steep slope; over-steepening of a slope by natural erosion or man made excavation; and, removal of vegetation roots, which hold topsoil together. Some rock types, such as shale and schist are more prone to slope failure than others. Sedimentary bedding planes, presence of fracturing, depth of weathering, presence of water, and bedrock mineral content can all affect slope stability.

Landslides occur in various forms, including slides, flows, avalanches and rock falls. Some forms move relatively slowly and although they are potentially very destructive, they are generally not life threatening. Other forms, especially debris avalanches and rock falls, move very rapidly and are quite dangerous.

Forest fires increase the chances of landsliding, by decreasing the amount of plant life, whose roots would normally promote slope stability by holding the topsoil together. Even if a landslide does not occur following a wildfire, runoff from precipitation may erode topsoil. Prescribed burns reduce the threat of catastrophic wildfires. Burn area rehabilitation helps to reduce the potential for erosion, landsliding, and the clogging of our streams and water reservoirs with sediment.

Over half of the land in Los Padres National Forest is either extremely or highly susceptible to slope failure, which makes it very important to study and understand landslides in the Forest. Some 250 active and hundreds more non-active landslide areas have been mapped across the Forest.

The earth is made up of a number of different layers, but the most important layer to understanding geology is the outer, solid crust of the planet. The earth's crust is made up of a number of large plates that rest on top of a more plastic, partially molten inner layer, the asthenosphere. Powered by convection currents deep within the earth, the plates move past, over, under and away from each other. The interaction of these plates with each other and the rest of the earth is what geologists call plate tectonics.

Tectonic plates can be composed of one or both of two types of crust, oceanic and continental. The relative motion of the plates combined with the two types of crust allows for a number of different interactions along plate boundaries. Plates collide, deforming into mountain ranges. Ocean floors are subducted under continental landmasses, where they break apart and melt adding to the asthenosphere. Plates can spread apart allowing molten material to well up and solidify into new crust. They can also slide past each other creating massive transverse fault zones. If you want to learn more about plate tectonics, the USGS has an excellent description of plate tectonic theory.

The San Andreas Fault, which runs through the Forest, is a contact between two tectonic plates sliding past each other: the Pacific Plate and the North American Plate. Since Los Padres National Forest straddles these two massive, moving blocks of the earth's crust, parts of the forest on the northern side of the San Andreas are moving to the southeast, while the southern side is moving to the northwest. Southern California, including much of the area covered by the Forest, has witnessed some incredibly unique tectonic plate interactions in its recent geologic history. Professor Tanya Atwater of the Geology Department at UC Santa Barbara is world renowned for her animations of tectonic plate history of southern California and the west coast. Check it out at her website

The Rock Cycle

Plate tectonics allows for another geologic concept known as the "rock cycle." Like all matter, rocks are never truly created nor destroyed, they are merely converted into another form. There are three different rock classifications:igneous, sedimentary and metamorphic. Igneous rocks form when molten rock, from lower layers in the earth, rises into the crust or all the way to the surface and cools into solid rock. Sedimentary rock, is made of sediments such as sand, clay, mud and gravel. These sediments are the products of weathering and erosion of older rocks into littler pieces. Through a process of deposition, compaction and cementation, these sediments are turned into new rocks like sandstone, limestone and shale. Metamorphic rocks form when a rock of any type is altered under intense pressure and/or high temperatures. These conditions occur deep within the crust, or along tectonic plate boundaries. A rock of any type, can be melted, eroded or metamorphosed. Thus any rock has the potential to be converted into a new rock of any of the three types. Rocks are continually being recycled, which is why the transformation is called the rock cycle: it never really ends!

The most common rock type exposed in Los Padres is sedimentary, especially sandstone and shale, although granite (igneous) and metamorphics are common on the Monterey and Mt. Pinos Districts. These metamorphic and igneous rocks make up some of the oldest rocks in the Forest, with some that were formed as long as 1.3 billion years ago. Even the oldest rocks are a part of the same rock cycle as the very youngest. Erosion in the mountains is constantly bringing sediments down into the streambeds, reservoirs and ultimately to the ocean, where the cycle of creating new sedimentary rocks continues.

Geology relates in some way to all our natural resources. It is important to understand and study its role in managing our National Forests. Geologic resources are an important factor influencing the management of natural resources. Fossil fuels lay buried within layers of sedimentary strata, as are fossils, and precious minerals and rocks. The porosity of different rock types and the fault and fracture systems affects groundwater flow and stream recharge. Different types of bedrock produce variable soil types, which determine what kind of plant and animal habitat is found in a given region. Of course, the rugged mountains and spectacular geology in the Forest is also a resource that attracts casual tourists, hard-core outdoor enthusiasts, and students.

Many people don't realize that there is far more fresh water underground than there is flowing on the earth's surface. For example, groundwater makes up an estimated 75% of the water used for agricultural, industrial and domestic use in Santa Barbara County. Groundwater is water that is trapped in the cracks and tiny pore spaces within rocks and sediments. Precipitation and surface runoff percolate through topsoil and down into open spaces within the earth's crust, until the water reaches an impermeable layer. Water continuously accumulates within the earth to form underground reservoirs, called aquifers. Groundwater interacts with geology, topography and surface runoff to form rivers and lakes. Understanding the rock structure and composition is important both for understanding how that groundwater affects vegetation growth, stream recharge and aquatic wildlife species, and in determining its availability for human use.

The volume of water in an aquifer is dependent upon its lateral extent, but also upon the volume of cracks and pore space in the aquifer's host rock. Different rock types have different volumes of pore spaces, which makes some rocks better aquifer hosts than others. Thus the bedrock geology in a given region affects how much groundwater there is and how deep it is to the water table. For example, some sandstone bedrock is very porous and capable of containing large volumes of water, while a dense, unfractured shale may act as an impermeable rock unit and restrict underground flow.

Both groundwater and dammed reservoirs in Los Padres National Forest provide drinking water for many of the surrounding communities. Forest Service campgrounds are generally supported by wells, which tap groundwater resources. The Forest Service regularly monitors its groundwater wells and surface water sources for quality. In Los Padres we are actively working to maintain and restore watersheds, so that they can continue to be both a habitat for fish and wildlife, and a resource providing clean, usable water.

Fossils are relics of life in the past and are found mostly in sedimentary rocks. There are three basic types of fossils:trace, replacement and actual lifeform. Trace fossils are imprints made by a living organism in the former surface of the earth, including things like animal tracks or an imprint where a leaf came to rest, before being covered over by the next layer of sediment. With trace fossils, nothing besides the imprint remains, so they are found as shapes along contacts between sedimentary layers. The second type, replacement fossils, are formed when an organism or part of an organism is buried within sedimentary strata and its original chemical make-up is altered by mineral solutions, which, molecule by molecule, replace organic compounds with more stable minerals such as silica or calcite. The end result is a rock hard replica of the original organism. A good example of a replacement fossil is petrified wood, which still looks like wood, but is composed of a variety of different silica minerals. The third type of fossil occurs when the original organic material is preserved, thus preserving the actual life form. An example of an actual lifeform fossil would be an insect trapped in amber.

Fossils from both land (terrestrial) and ocean (marine) origins are common in the Los Padres. Clams, oysters and snail fossils are abundant in some sandstones and shales. Microscopic marine fossils (foraminifera) are often found in shale. Whale bones, fish, and other marine vertebrate fossils are most widespread in the Monterey Formation. Terrestrial vertebrate fossils such as camel, three toed horses, turtles and rodents have been found in the Cuyama Valley area. Numerous other types of fossils have been collected and studied over the years, some of which are on display at various southern California museums and educational institutions.

Collection of invertebrate (without backbone) fossils for personal, scientific, or educational use is permitted in the Forst, except where otherwise prohibited (e.g. wilderness areas). Collection of vertebrate fossils is only allowed by permit, and only by authorized museums and universities, which have access to the facilities for curation and storage. Collection of any fossil from National Forest lands for commercial use is prohibited.

Find out more about the USDA policy for collecting fossils at the national US Forest Service website for minerals and geology management

Dating back to the California Gold Rush, Los Padres National Forest has a rich history of mining on its lands. Minerals are really only rocks with an ascribed value based upon human demand for them, which is usually a function of their usefulness. Although they may not be of commercial value, there are many beautiful rocks and minerals to be found on the Forest. Federal regulations define minerals in three categories:locatable, leaseable, saleable. The laws, regulations and policies governing these categories are distinct, although in all cases, extraction is to be accomplished in an environmentally sound manner. To find out about the policy for mining and mineral collection in Forest land, visit the US Forest Service national site for minerals and geology management.

Locatable minerals found in Los Padres include: gold, copper, zinc, chrome, antimony, silver, uranium, mercury and limestone. Leasable minerals include oil and gas, phosphate, and gypsum. Saleable minerals include sand, gravel and building stone. While panning for gold used to be a profitable business on forest, now most gold deposits have been exploited. Mineral resources being excavated in large quantities in the Forest are limestone, bentonite, oil and gas, as well as mineral materials such as gravel, sand and clay for use in construction.

While the Forest is committed to fostering the development of important minerals and mineral materials, it is also dedicated to preserving the earth's natural environment and reducing human impact on plants and wildlife. Abandoned mines can be a safety hazard for the public and may damage watersheds. Abandoned mine reclamation is a significant part of Forest management; Los Padres is restoring one to two sites a year.

Fossil fuels, such as oil, gas and coal form from decomposing organic matter that is buried under sedimentary layers and compacted under the heavy weight of the overlying rock. Coal beds and oil fields of today were the forests and wetlands of millions of years ago. Petroleum is stored in the pore spaces and cracks of sedimentary rocks, often called oil shale or oil sands. In this respect, an oil field is quite similar to a groundwater aquifer, except oil is less dense than water which caused petroleum products to work their way upwards within the earth's surface and get trapped under non-porous confining layers.

Oil fields are most often located by combining subsurface geophysical data with drilling log results and geologic mapping. Then, to extract the oil and gas, a hole is drilled into the oil bearing rock and a pump on the surface extracts the black gold. Oil and gas production account for the majority of the Forest's energy production. Los Padres is the only National Forest in California with commercial petroleum reserves and the wells have been providing oil and gas for many years. Oil well placement on Forest land incorporates directional drilling and other measures that insure protection of surface resources and minimize visual impacts.