# Geology

The USGS provides accurate geologic maps and geologic information that forms the critical framework for understanding everything from environmental change to natural hazards.

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#### I think I found a meteorite. How can I tell for sure?

Meteorites are fragments of rock or metal that fall to Earth from space. They are very rare, but many people find unusual rocks or pieces of metal and wonder if they might have found a meteorite.Meteorites have several properties that help distinguish them from other rocks:Density: Meteorites are usually quite heavy for their size, since they contain metallic iron and dense minerals.Magnetic...

#### I think I found a meteorite. How can I tell for sure?

Meteorites are fragments of rock or metal that fall to Earth from space. They are very rare, but many people find unusual rocks or pieces of metal and wonder if they might have found a meteorite.Meteorites have several properties that help distinguish them from other rocks:Density: Meteorites are usually quite heavy for their size, since they contain metallic iron and dense minerals.Magnetic...

#### I have (or think I have) a sinkhole on my property. What should I do?

While the USGS studies the types of rocks that can potentially form sinkholes, we don’t investigate individual sinkholes on private property. First, rule out human causes for your feature. Some sinkholes are caused by leaky underground pipes (talk to your utility company) and some are old construction pits or other buried materials that have settled. If you’re confident of a natural cause for your...

#### I have (or think I have) a sinkhole on my property. What should I do?

While the USGS studies the types of rocks that can potentially form sinkholes, we don’t investigate individual sinkholes on private property. First, rule out human causes for your feature. Some sinkholes are caused by leaky underground pipes (talk to your utility company) and some are old construction pits or other buried materials that have settled. If you’re confident of a natural cause for your...

#### Can you identify my rock or mineral?

Rocks and minerals must be examined in person from all perspectives for accurate identification; they are extremely difficult to identify through photographs. You will get the best results by taking your rock or mineral to a local source where it can be handled and examined closely. Possibilities include:Your state geological surveyA natural science museumA college or university with a geology...

#### Can you identify my rock or mineral?

Rocks and minerals must be examined in person from all perspectives for accurate identification; they are extremely difficult to identify through photographs. You will get the best results by taking your rock or mineral to a local source where it can be handled and examined closely. Possibilities include:Your state geological surveyA natural science museumA college or university with a geology...

#### How can I find original field notes made by USGS geologists and geographers?

The USGS Field Records Collection is an archive of unpublished field notes, maps, correspondence, manuscripts, analysis reports, and other data created or collected by USGS Geology Discipline scientists during field studies and other project work. The collection is located in the USGS Library in Denver, Colorado, and is available for on-premises examination during normal library hours. See the...

#### How can I find original field notes made by USGS geologists and geographers?

The USGS Field Records Collection is an archive of unpublished field notes, maps, correspondence, manuscripts, analysis reports, and other data created or collected by USGS Geology Discipline scientists during field studies and other project work. The collection is located in the USGS Library in Denver, Colorado, and is available for on-premises examination during normal library hours. See the...

#### Where can I obtain soil surveys?

A soil survey is the systematic description, classification, and mapping of soils in an area. They are published by the USDA Natural Resources Conservation Service (NRCS), formerly known as the Soil Conservation Service.NRCS soil surveys are available from several sources:Some are on the NRCS website.Published soil surveys can be found at some libraries or borrowed through interlibrary loan...

#### Where can I obtain soil surveys?

A soil survey is the systematic description, classification, and mapping of soils in an area. They are published by the USDA Natural Resources Conservation Service (NRCS), formerly known as the Soil Conservation Service.NRCS soil surveys are available from several sources:Some are on the NRCS website.Published soil surveys can be found at some libraries or borrowed through interlibrary loan...

#### How did Half Dome, the massive rock monument in Yosemite National Park, acquire its unique shape?

At the head of the valley in Yosemite National Park - as if on a pedestal - stands Half Dome. It is smoothly rounded on three sides and a sheer vertical face on the fourth. Half Dome, which stands nearly 8,800 feet (2,682 meters) above sea level, is composed of granodiorite, and is the remains of a magma chamber that cooled slowly and crystallized thousands of feet beneath the Earth's surface. The...

#### How did Half Dome, the massive rock monument in Yosemite National Park, acquire its unique shape?

At the head of the valley in Yosemite National Park - as if on a pedestal - stands Half Dome. It is smoothly rounded on three sides and a sheer vertical face on the fourth. Half Dome, which stands nearly 8,800 feet (2,682 meters) above sea level, is composed of granodiorite, and is the remains of a magma chamber that cooled slowly and crystallized thousands of feet beneath the Earth's surface. The...

#### What is the difference between a sinkhole and a pothole?

A sinkhole is a closed natural depression in the ground surface caused by removal of material below the ground and either collapse or gradual subsidence of the surface into the resulting void.A pothole is usually a fairly small feature caused by failure of paving materials, usually associated with roads, parking lots, and airports. In the colder parts of the country, potholes become more abundant...

#### What is the difference between a sinkhole and a pothole?

A sinkhole is a closed natural depression in the ground surface caused by removal of material below the ground and either collapse or gradual subsidence of the surface into the resulting void.A pothole is usually a fairly small feature caused by failure of paving materials, usually associated with roads, parking lots, and airports. In the colder parts of the country, potholes become more abundant...

#### What is the largest sinkhole in the United States?

There are some very large, ancient, ‘inactive’ sinkholes in some areas of the U.S. that are thousands of years old. Alabama claims to have the largest recent collapse sinkhole. It is called the “Golly Hole” and is located in Shelby County in the central part of the state. It collapsed suddenly in 1972. The sinkhole is about 325 feet long, 300 feet wide, and 120 feet deep.Learn more: USGS Water...

#### What is the largest sinkhole in the United States?

There are some very large, ancient, ‘inactive’ sinkholes in some areas of the U.S. that are thousands of years old. Alabama claims to have the largest recent collapse sinkhole. It is called the “Golly Hole” and is located in Shelby County in the central part of the state. It collapsed suddenly in 1972. The sinkhole is about 325 feet long, 300 feet wide, and 120 feet deep.Learn more: USGS Water...

#### What is the difference between a sinkhole and land subsidence?

Sinkholes are just one of many forms of ground collapse, or subsidence. Land subsidence is a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials. The principal causes of land subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost. Land...

#### What is the difference between a sinkhole and land subsidence?

Sinkholes are just one of many forms of ground collapse, or subsidence. Land subsidence is a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials. The principal causes of land subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost. Land...

#### How many sinkholes open up in a year?

There is no database of sinkhole collapses for the United States, so these data are unavailable. Some individual state geologic surveys track reported collapses within their state. Many sinkhole collapses are not reported to authorities or news organizations, and many occur in rural areas where they are unobserved.Learn more: USGS Water Science School - Sinkholes

#### How many sinkholes open up in a year?

There is no database of sinkhole collapses for the United States, so these data are unavailable. Some individual state geologic surveys track reported collapses within their state. Many sinkhole collapses are not reported to authorities or news organizations, and many occur in rural areas where they are unobserved.Learn more: USGS Water Science School - Sinkholes