DESCRIPTION
This system consists of geologic elements including soils and bedrock and their related processes. It serves as the skeleton upon which all of the other systems function. It is about the land—they way we use it, manipulate it, and often work at cross purposes with the intrinsic qualities and cues of the broader landscape. In countless ways, the geologic system has played a role in defining the patterns and processes of urban environments throughout history.

GEOLOGIC FUNCTIONS
Support: the geologic system is supporting our movements and agendas in a real, physical way. Indeed, the stability of the geologic system is, for most people, one of the “givens". We expect stability, structure, permanance.
Erosion and depostition: erosion is a natural function of the geologic system. Trough glaciation, wind and rain erosion moves particles around on the planet. It is how river deltas are formed and how places like the Grand Canyon came to be. Erosion softens mountains countours or shifts the sands of desert dunes. Humans have dramatically altered these processes. Not protecting job sites using techniques like erosion and sediment control, or channelizing rivers so that soil deposition does not occur in estuarine wetlands can seriously damage ecosystems and undermine civilizations.
Substrate creation: in order for erosion to occur, the geologic system needs the raw materials: the bedrock, the stone that forms the substrate of the system. Recall that there are three primary ways that substrate is made: (1) igneous rock occurs as magma cools. (2) In some places, that igneous rock is covered by sedimentary rock, which was created over millenia as stones were compressed, compacted and cemented together. And finally, there are (3) metamorphic rocks which are igneous or sedimentary rocks that have changed form due to environmental conditions. Slate and shist are two examples of metamorphic stone.
Soil formation: As substrate formation occurs and erosion wears it down, soil is created. Whereas stone is inert and dead, soil is alive with microbes, bacteria, and nutrients. It forms the basis for life on earth.
Natural hazard-mitigation: the geologic system provides us with mechanisms to help mitigate threats like earthquakes, mudslides, tsunamis, hurricanes. In part, it means avoiding them by not building on steep slopes or above fault lines. But natural hazard mitigation also means keeping intact those strong collaborations between the geologic and biologic systems that naturally absorb and buffer us from many of these dramatic disturbances. Wetlands, dunes, and vegetation on steep slopes are but some of the examples. Another example involves the removal of wetlands off the coast of Louisiana. According to some, the Mississippi Gulf River Outlet Canal (constructed by the U.S. Army of Engineers beginning in 1956) formed a superhighway, leading the way for Hurricane Katrina to strike New Orleans in 2005.
Soil drainage: Depending on the use, sometimes it is best to have a soil that drains quickly (i.e. for structures and roads) other times a slow draining soil (i.e. agricultural uses); it really depends on the use. In the United States, arguably the best source of information of regarding soil drainage is the Natural Resources Conservation Service, particularly on lands devoted to agriculture.
Surface drainage.

PERFORMANCE METRICS
Slope: slope determines what can be built, gives an indication of stability and locates us in place. It can be an asset, creating defensible, but arable land , like for the Incas near Machu Picchu in Peru.
Soil type and its ability to support other green infrastructure systems: big determinant of geologic system stability. Typically classified in the textural triangle, soils are broken into three main types: clay, sand and silt. Different soil types are good for different tasks and understanding their properties is important. Sandy soil, for example, is excellent for infiltrating stormwater, while silty soils hold onto water making them some of the most fertile soils in the world. Soil types also determine infiltration rates, allowing for an understanding of the way that the hydrologic system can, and will, interact with the geologic system.
Depth to bedrock: it can be another important measure of the geologic system’s performance, particularly when we need to anchor to the earth.
Seismic activity: it is a dramatic disturbance from the norm. In some places, seismic activity regularly shakes and reshapes our urban environment often times in tragic ways. Our ability to map and understand seismic patterns has grown and we have the ability to assess risk from fault zones and to engineer infrastructures to mitigate risk. These important technical advances must be shared with the developing world, especially in regions of known seismic activity.
Evaluation of other underlying forces such as seismic lines, crescent volcanics and other aspects of the land that may affect cities.An important metric are the geologically hazardous areas regulations, which have as primary purpose to avoid and minimize potential impacts to life and property from geologic hazards. Geologically hazardous areas include areas susceptible to erosion, earthquakes, volcanic eruptions, earth and mudslides, tsunamis, hurricanes or other geological events.

CASE STUDIES: PLANNING AND POLICY

1. Soil BMP in Washington -- A document with links to the WA State Soil BMP and where Soil BMPs are required in Western Washington.
   
2. Soil Erosion Prediction Technology -- A keynote discussing erosion prediction technology as a part of and tool for conservation planning.
   
3. Soil Erosion and Sediment Control Act-- The state of New Jersey's Soil Erosion and Sediment Control Act. Could serve as a jumping off point for other municipalities/states.
4. Mt. Rainier Volcanic Hazards Response-- Volcano Response Plan for Mt. Rainier.
   

CASE STUDIES: HIGH PERFORMANCE LANDSCAPES

GEOLOGIC SYSTEM RESOURCES

1. U.S. Geological Survey
2. Geology of North America
3. Building soil
4. USDA Web Soil Survey