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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Digital Geologic Map of Alaska
An exhaustive database (NGMDB) that provides bibliographic access to thousands of geologic, geophysical, and other kinds of maps available in USGS publications, Web sites, and in popular science journals. 
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The USGS Field Records Collection is an archive of unpublished field notes, maps, correspondence, manuscripts, analysis reports, and other data created or collected by USGS Geology Discipline scientists during field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 ...
Samples to OGRL thumbnail
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...
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
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 types of rock below the land surface...
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...