Frequently Asked Questions

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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Image: New Accessions Arriving at Field Records
The USGS Field Records Collection is an archive of unpublished field notes, maps, correspondence, manuscripts, analysis reports, and other data created or collected by USGS Geology Discipline scientists during field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 ...
Image: Moon over Half Dome Panorama
At the head of the valley in Yosemite National Park - as if on a pedestal - stands Half Dome, the most colossal and recognizable rock monument in the Sierra Nevada, 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 quartz monzonite, and...
Image: Various Karst Features Along Peace River, Fl
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...
Image: Sinkholes in West-central Florida, Freeze Event of 2010
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...
Image: Winter Park Florida Sinkhole of 1981
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...
Image: Sinkholes in West-central Florida, Freeze Event of 2010
Sinkhole damages over the last 15 years cost on average at least $300 million per year. Since there is no national tracking of sinkhole damage costs, this estimate is probably much lower than the actual cost.
Image: Sinkholes in West-central Florida, Freeze Event of 2010
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.
Image: Winter Park Florida Sinkhole of 1981
What are sinkholes?   A sinkhole is a depression in the ground that has no natural external surface drainage. Basically this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface. Sinkholes are most common in what geologists call, “karst terrain.” These are regions where the type of rock...
Image: USGS Snowmastodon Research
Paleontologists don't know for certain, but perhaps a large body size protected them from most predators, helped to regulate internal body temperature, or let them reach new sources of food (some probably browsed treetops, as giraffes do today). No modern animals except whales are even close in size to the largest dinosaurs; therefore,...
Geologic time periods
Dinosaurs lived on all of the continents. At the beginning of the age of dinosaurs (during the Triassic Period, about 230 million years ago), the continents were arranged together as a single supercontinent called Pangea. During the 165 million years of dinosaur existence this supercontinent slowly broke apart. Its pieces then spread across the...
Image: Mastodon Fossil
Dinosaurs went extinct about 65 million years ago (at the end of the Cretaceous Period), after living on Earth for about 165 million years. If all of Earth time from the very beginning of the dinosaurs to today were compressed into 365 days (1 calendar year), the dinosaurs appeared January 1 and became extinct the third week of September. (Using...
Earth in motion
From about 280-230 million years ago, (Late Paleozoic Era until the Late Triassic) the continent we now know as North America was continuous with Africa, South America, and Europe. Pangea first began to be torn apart when a three- pronged fissure grew between Africa, South America, and North America. Rifting began as magma welled up through the...