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USGS2025

USGS—An Unparalleled Scientific Asset

The U.S. Geological Survey (USGS) delivers information critical to powering our economy, managing our natural resources, and keeping Americans safe and healthy. 1 Mapping the Nation $21B Geologic maps save users an estimated 15% in annual costs: a value of between $14B and $21B. $25.6B in annual value to users of imagery from Landsat satellites, which were codeveloped by NASA and the USGS and operated through their lifespans by the USGS. $13.5B in annual benefits is generated by the USGS's 3D Elevation Program. Securing America’s Energy Independence 44% USGS-identified undiscovered geothermal energy is equal to 44% of current U.S. electricity generation. 29.4B barrels of oil and 391.6 trillion cubic feet of gas in recoverable resources are available on U.S. public lands based on USGS assessments. Protecting Americans’ Health and Safety $424B in recent wildland fire damages highlight the need for USGS fire science, which supports efforts to protect communities and reduce risk. USGS earthquake, volcano, landslide, and coastal hazard monitoring and information save lives and minimize costs; for example, $2.8M can be saved because of USGS enhanced information about a Mauna Loa eruption. $4.5B is the estimated cost of annual flooding. Through a network of over 11,885 streamgages, the USGS supports public safety and enables forecasts, early warning systems, and management actions that protect lives and property. Supporting National Security $3.1B The USGS identified a $3.1B risk to the American economy if China restricts gallium imports. This is one example underscoring the importance of the USGS mapping critical minerals, investigating supply chains, and producing the Nation’s critical minerals list. Enhancing Our Lands and Waters $21B in estimated annual costs results from invasive species. The USGS’s invasive species research informs approaches used to reduce their effects on agriculture, water infrastructure, disease transmission, fisheries, and outdoor recreation. USGS innovations support early warnings for harmful algal blooms—over $2M in yearly benefits are provided to Kansas alone. $45B USGS science informs the management of big game (such as deer and elk). The big-game hunting industry contributes $45B to the U.S. economy. Fostering American Prosperity $4.1T Mineral commodities are necessary for the $4.1T in value added to the GDP by major industries that consume processed mineral materials and employ 1 million workers. Because of this, USGS data on mineral supply, demand, and trade are highly valued. 45,000 metric tons Rare earths power the growing technology economy, including cell phones, electric vehicles, and medical devices. For over 70 years, USGS work has supported the discovery of rare earth resources in California’s Mountain Pass area, which produced 45,000 metric tons of rare earth concentrates in 2024—over 11% of the global supply. Guarding American Food Security $70.2B USGS science informs early warning systems and management strategies to mitigate disease outbreaks in agriculture—critical research on highly pathogenic avian influenza, for example, helps safeguard the $70B value in poultry and egg production. $11.8B USGS groundwater tools are vital for agriculture; for example, in the Mississippi Alluvial Plain, 65% of farming relies on groundwater to support its $11.8B annual industry. 1 Values throughout are given in billions (B), millions (M), and trillions (T) of U.S. dollars. GDP is “Gross Domestic Product.” Percentages are shown as %.

General Information Product↗
USGS1989

Surficial geologic map of the Meeker 30' x 60' quadrangle, Garfield, Moffat, Rio Blanco and Routt Counties, Colorado

This map is one of a series of four 30' x 60' surficial geologic maps (1:100,000 scale) intended to provide basic geologic information for planning for energy resource development and growth in northwestern Colorado. An effort is made to characterize all surficial materials, regardless of origin. Hence, residuum is given much more emphasis than is customary, and this results in several departures from conventional geologic maps: bedrock geology is deemphasized; the part of the map symbol denoting geologic age is omitted for surficial units because all surficial units shown are believed to be of Quaternary age; and faults are not shown because none in this map area was observed to displace surficial materials. Few exposures of most map units exist, except in manmade excavations, such as gravel pits and road cuts. Consequently, thicknesses usually are estimated, and data on stratification, clast size, and relative proportions of matrix and framework clasts are limited to a few localities for each map unit. The Wentworth scale is used to describe grain sizes. Mapping was done chiefly on aerial photographs taken in 1953. Hence, landslides and modifications resulting from gravel mining since 1953 may not show on this map. The scales of the aerial photographs (about 1:60,000) and the map (1:100,000) governed the minimum size of the deposits mapped. The minimum thickness of the depostis mapped is about 1.5m in most places. Deposit thickness, although not a mapping criterion, influences the topographic expression of many landforms, and landform is the basis for delineating the surficial deposits shown.

Colorado↗
USGS1991

Surficial geologic map of the Walden 30' x 60' quadrangle, Jackson, Larimer, and Routt counties, Colorado

This map is one of a series of four 30' x 60' surficial geologic maps (1:100,000 scale) intended to provide basic geologic information for planning for energy resource development and growth in northwestern Colorado. An effort is made to characterize all surficial materials, regardless of origin. Hence, residuum is given much more emphasis than is customary, and this results in several departures from conventional geologic maps: bedrock geology is deemphasized; the part of the map symbol denoting geologic age is omitted for surficial units because all surficial units shown are believed to be of Quaternary age; and faults are not shown because none in this map area was observed to displace surficial materials. Few exposures of most map units exist, except in manmade excavations, such as gravel pits and road cuts. Consequently, thicknesses usually are estimated, and data on stratification, clast size, and relative proportions of matrix and framework clasts are limited to a few localities for each map unit. The Wentworth scale is used to describe grain sizes. Mapping was done chiefly on aerial photographs taken in 1953. Hence, landslides and modifications resulting from gravel mining since 1953 may not show on this map. The scales of the aerial photographs (about 1:60,000) and the map (1:100,000) governed the minimum size of the deposits mapped. The minimum thickness of the depostis mapped is about 1.5m in most places. Deposit thickness, although not a mapping criterion, influences the topographic expression of many landforms, and landform is the basis for delineating the surficial deposits shown.

Colorado↗
USGS1991

Surficial geologic map of the Steamboat Springs 30' x 60' quadrangle, Grand, Jackson, and Routt counties, Colorado

This map is one of a series of four 30' x 60' surficial geologic maps (1:100,000 scale) intended to provide basic geologic information for planning for energy resource development and growth in northwestern Colorado. An effort is made to characterize all surficial materials, regardless of origin. Hence, residuum is given much more emphasis than is customary, and this results in several departures from conventional geologic maps: bedrock geology is deemphasized; the part of the map symbol denoting geologic age is omitted for surficial units because all surficial units shown are believed to be of Quaternary age; and faults are not shown because none in this map area was observed to displace surficial materials. Few exposures of most map units exist, except in manmade excavations, such as gravel pits and road cuts. Consequently, thicknesses usually are estimated, and data on stratification, clast size, and relative proportions of matrix and framework clasts are limited to a few localities for each map unit. The Wentworth scale is used to describe grain sizes. Mapping was done chiefly on aerial photographs taken in 1953. Hence, landslides and modifications resulting from gravel mining since 1953 may not show on this map. The scales of the aerial photographs (about 1:60,000) and the map (1:100,000) governed the minimum size of the deposits mapped. The minimum thickness of the depostis mapped is about 1.5m in most places. Deposit thickness, although not a mapping criterion, influences the topographic expression of many landforms, and landform is the basis for delineating the surficial deposits shown.

Colorado↗
USGS2000

Geologic map of the Sasquatch Steps area, north flank of Mount St. Helens, Washington

The 1980 eruption of Mount St. Helens resulted in both new volcanic deposits and deeply incised exposures into pre-1980 deposits. These exposures were produced by excavation of the crater by the 1980 landslides and lateral explosion as well as the subsequent erosion of Step and Loowit creeks by northerly stream flow out of the horseshoe-shaped crater. The map covers the area known as the Sasquatch Steps (commonly called the Steps), which lies between the Pumice Plain on the north and the lowermost portion of the crater on the south. Rapid alluvial aggradation at the base of the Steps is presently burying some of the lowest exposures, and erosion is stripping many of the upland deposits. The stratigraphic sequence exposed in the map area includes deposits from the eruptive periods listed in table 1 (Crandell, 1987). Assignment of deposits to the various eruptive periods is based on lithology and ferromagnesian-mineral suites typical for each of the eruptive periods (Mullineaux and Crandell, 1981; Mullineaux, 1986), as well as three 14 C dates from wood found in the deposits. Faults displayed on the map are largely confined to the older part of the stratigraphic section. These older units are highly shattered, with an extremely complicated fracture pattern, and it is only possible to show the largest and most distinctive of these structures at the map scale. Interpretation of the stratigraphy and structure of this area is given in Hausback and Swanson (1990).

Washington↗
USGS1995

Geologic map of Arsia Mons Volcano, Mars

The geologic map shows the flanks and summit caldera of Arsia Mons, the southernmost of three large shield volcanoes ( Arsia , Pavonis, and Ascrae us Montes) that form the Tharsis Montes volcanic chain (fig. 1). The volcanoes lie along the cre st of a regional northeast-trending rise that extends more than 3,000 km along or near the planet-wide boundary that separates th e southern highlands from the northern lowlands. Previous geologic mapping of this region (Scott and others, 1981; Scott and Tanaka, 1986) shows six major lava flows that were extruded from the Tharsis volcanoes during the Early Hespe rian to Late Amazonian Epochs; the flows cover and area exceeding 7x10 6 km 2 around the volcanic centers. All of these flows – mapped as members of the Tharsis Montes Formation – are pre sent in the map area. Broad, fan-shaped surficial deposits that resemble landslides extend down the northwest sides of each volcano and of Olympus Mons, about 1,500 km northwest of Arsia Mons (fig. 1). The largest of these gently sloping, lobate deposits is on Arsia Mons, where ambiguous relations bet wee n one facies of the fan-shaped accumulations and underlying topographic features have provoked questions as to the origin of the deposits.

IMAP↗
USGS1998

Geologic map of the western Ophir Planum region (MTM -10067) of Mars

The map area, in the Coprates 1:2,000,000-scale quadrangle MC-18 NW lies in the heart of the Valles Marineris trough system. The western part of Ophir Planum (36,660 km 2 ) occupies 40 percent of the map areas; parts of Candor , Melas, and Coprates Chasmata make up the remainder. The troughs contain distinct ive landslide deposits, normal faults, possible young volcanic rocks, and layered materials. Ophir Planum plateau is deformed by normal faults and grabens in an en echelon array that is unique along the Valles Marineris .

IMAP↗
USGS2002

Geologic Map of the Diana Chasma Quadrangle (V-37), Venus

Introduction The Diana Chasma quadrangle (V-37), an equatorial region between 0° to 25° S. and 150° to 180° E. that encompasses ~8,400,000 km 2 , is broadly divided into southern Rusalka Planitia in the north, eastern Aphrodite Terra in the central region, and unnamed regions to the south. Geologic mapping constrains the temporal and spatial relations of the major features, which include a tessera inlier, Markham crater, six large coronae (300-675 km diameter), four smaller coronae (150-225 km diameter), Diana and Dali chasmata, a large fracture zone, and southern Rusalka Planitia. Eastern Aphrodite Terra, marked here by large coronae, deep chasmata, and an extensive northeast-trending fracture zone, extends from Atla Regio to Thetis Regio. The large coronae are part of a chain of such features that includes Inari Corona to the west-southwest and Zemina Corona to the northeast. V-37 quadrangle is bounded on the north by Rusalka Planitia and on the south by Zhibek Planitia. International Astronomical Union (IAU) approved and provisional nomenclature and positions for geographic features within Diana Chasma quadrangle are shown on the geologic map. [Note: Atahensik Corona was referred to as Latona Corona in much previously published literature.] Diana Chasma quadrangle hosts some of the steepest topography on Venus. Altimetry measurements range from -2.5 to 4.7 km (0.0 = mean planetary radius), with a surface mean of 0.6 km. Fractures and faults within the central fracture/rift zone create large blocks of down-dropped material, especially along the east-central edge of the map area. The Dali and Diana chasmata display slopes of >30°, the steepest and deepest trenches on Venus. Both chasmata host landslide deposits presumably sourced from the steep chasmata walls. The tessera inlier, coronae, and ridge belts sit topographically above Rusalka and Zhibek planitiae. Rusalka Planitia topography describes broad undulations having northwest-trending ridges spaced ~200 km apart. The most distinctive ridge, Vetsorgo Dorsum, centered at 6.5° S., 163° E., is a Class I ridge belt owing to its simple arch morphology. The central interior of Markham crater sits topographically lower than the surrounding region, which slopes downward to the east.

IMAP↗
USGS2003

Geologic map of the Hogback Mountain quadrangle, Lewis and Clark and Meagher Counties, Montana

The geologic map of the Hogback Mountain quadrangle, scale 1:24,000, was made as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Hogback Mountain area, rocks ranging in age from Middle Proterozoic through Cretaceous are strongly folded within and under thrust plates of equivalent rocks. Continental rocks of successive thrust plates have been telescoped eastward over a buttress of the stable continent. Erosional remnants of Oligocene andesitic basalt lie on highest surfaces eroded across the strongly deformed older rocks; younger erosion has dissected the terrain deeply, producing Late Tertiary and Quaternary deposits of alluvium, colluvium, and local landslide debris in the valleys and canyons. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part of the quadrangle at the lowest structural level, rocks of the Upper Mississippian Big Snowy Group, including the Kibbey Formation and the undivided Otter and Heath Formations, the overlying Pennsylvanian Amsden and undivided Quadrant and Phosphoria Formations, the Ellis Group, and the Kootenai Formation, are folded and broken by thrust faults. The next higher structural level, the Avalanche Butte thrust plate, exposes strongly folded and, in places, attenuated strata of Cambrian (Flathead Sandstone, Wolsey Shale, Meagher Limestone, and undivided Pilgrim Formation and Park Shale), Devonian (Maywood Formation, Jefferson Formation, and most of the Three Forks Formation), and Mississippian (uppermost part of the Three Forks Formation and Lodgepole and Mission Canyon Limestones) ages. The overlying Hogback Mountain thrust plate contains strongly folded rocks ranging in age from the Middle Proterozoic Greyson Formation to the Upper and Lower Mississippian Mission Canyon Limestone and Cretaceous diorite sills. The highest structural level, the Moors Mountain thrust plate, contains the Middle Proterozoic Greyson and Newland Formations and discontinuous Upper Proterozoic diabase sills. Rocks are complexly folded and faulted across the quadrangle. At the lowest level in the northeastern part of the quadrangle, Upper Mississippian and younger strata are folded along northwest-trending axes and broken by thrust faults that at outcrop level displace the same rocks. The central core of the quadrangle is formed by the Avalanche Butte thrust plate, which contains recumbently folded and thrust faulted Paleozoic rocks. A succession of four tight recumbent folds within the plate have axial traces that trend northwest and north-northwest, and that are both arched and downfolded along east- and northeast-trending axes. Carbonate rocks of the Mission Canyon and Lodgepole Limestones in the upper part of the Avalanche Butte thrust plate exposed in the canyon of Trout Creek are folded and attenuated in stacked east-directed recumbent folds that developed as a succession of folded duplex thrust slices. The exposed remnant of the next higher structural level, the Hogback Mountain thrust plate, contains northeast- and east-trending folds that are inverted on the upper overturned limb of a younger northwest-trending recumbent fold. The Hogback Mountain thrust fault is itself folded and, in its northernmost exposures, is overturned to dip west beneath the overlying Moors Mountain thrust plate. During post-middle Tertiary deformation, the Hogback Mountain thrust fault moved as a normal fault, down on the east. The structurally highest Moors Mountain thrust plate rests on the Avalanche Butte thrust plate in the southwestern part of the quadrangle and across both the Avalanche Butte and Hogback Mountain thrust plates along the northwest edge of the quadrangle. In the central eastern part of the map area, the edge of a large klippen of the Moors Mounta

IMAP↗
USGS2003

Geologic map of the Nelson quadrangle, Lewis and Clark County, Montana

The geologic map of the Nelson quadrangle, scale 1:24,000, was prepared as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Nelson area, rocks ranging in age from Middle Proterozoic through Cretaceous are exposed on three major thrust plates in which rocks have been telescoped eastward. Rocks within the thrust plates are folded and broken by thrust faults of smaller displacement than the major bounding thrust faults. Middle and Late Tertiary sedimentary and volcaniclastic rocks unconformably overlie the pre-Tertiary rocks. A major normal fault displaces rocks of the western half of the quadrangle down on the west with respect to strata of the eastern part. Alluvial and terrace gravels and local landslide deposits are present in valley bottoms and on canyon walls in the deeply dissected terrain. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part, strata of the Middle Cambrian Flathead Sandstone, Wolsey Shale, and Meagher Limestone, the Middle and Upper Cambrian Pilgrim Formation and Park Shale undivided, the Devonian Maywood, Jefferson, and lower part of the Three Forks Formation, and Lower and Upper Mississippian rocks assigned to the upper part of the Three Forks Formation and the overlying Lodgepole and Mission Canyon Limestones are complexly folded and faulted. These deformed strata are overlain structurally in the east-central part of the quadrangle by a succession of strata including the Middle Proterozoic Greyson Formation and the Paleozoic succession from the Flathead Sandstone upward through the Lodgepole Limestone. In the east-central area, the Flathead Sandstone rests unconformably on the middle part of the Greyson Formation. The north edge, northwest quarter, and south half of the quadrangle are underlain by a succession of rocks that includes not only strata equivalent to those of the remainder of the quadrangle, but also the Middle Proterozoic Newland, Greyson, and Spokane Formations, Pennsylvanian and Upper Mississippian Amsden Formation and Big Snowy Group undivided, the Permian and Pennsylvanian Phosphoria and Quadrant Formations undivided, the Jurassic Ellis Group and Lower Cretaceous Kootenai Formation. Hornblende diorite sills and irregular bodies of probable Late Cretaceous age intrude Middle Proterozoic, Cambrian and Devonian strata. No equivalent intrusive rocks are present in structurally underlying successions of strata. In this main part of the quadrangle, the Flathead Sandstone cuts unconformably downward from south to north across the Spokane Formation into the upper middle part of the Greyson Formation. Tertiary (Miocene?) strata including sandstone, pebble and cobble conglomerate, and vitric crystal tuff underlie, but are poorly exposed, in the southeastern part of the quadrangle where they are overlain by late Tertiary and Quaternary gravel. The structural complexity of the quadrangle decreases from northeast to southwest across the quadrangle. At the lowest structural level (Avalanche Butte thrust plate) exposed in the canyon of Beaver Creek, lower and middle Paleozoic rocks are folded in northwest-trending east-inclined disharmonic anticlines and synclines that are overlain by recumbently folded and thrust faulted Devonian and Mississippian rocks. The Mississippian strata are imbricated adjacent to the recumbent folds. In the east-central part of the quadrangle, a structurally overlying thrust plate, likely equivalent to the Hogback Mountain thrust plate of the Hogback Mountain quadrangle adjacent to the east (Reynolds, 20xx), juxtaposes recumbently folded Middle Proterozoic and unconformably overlying lower Paleozoic rocks on the complexly folded and faulted rocks of the Avalanche Butte thrust plate. The highest structural plate, bounded below

IMAP↗
USGS2002

Geologic Map of the Katmai Volcanic Cluster, Katmai National Park, Alaska

This digital publication contains all the geologic map information used to publish U.S. Geological Survey Geologic Investigations Map Series I-2778 (Hildreth and Fierstein, 2003). This is a geologic map of the Katmai volcanic cluster on the Alaska Peninsula (including Mount Katmai, Trident Volcano, Mount Mageik, Mount Martin, Mount Griggs, Snowy Mountain, Alagogshak volcano, and Novarupta volcano), and shows the distribution of ejecta from the great eruption of June, 1912 at Novarupta. Widely scattered erosional remnants of volcanic rocks, unrelated to but in the vicinity of the Katmai cluster, are also mapped. Distribution of glacial deposits, large landslides, debris avalanches, and surficial deposits are a snapshot of an ever-changing landscape.

IMAP↗
USGS2003

Hawaii's volcanoes revealed

Hawaiian volcanoes typically evolve in four stages as volcanism waxes and wanes: (1) early alkalic, when volcanism originates on the deep sea floor; (2) shield, when roughly 95 percent of a volcano's volume is emplaced; (3) post-shield alkalic, when small-volume eruptions build scattered cones that thinly cap the shield-stage lavas; and (4) rejuvenated, when lavas of distinct chemistry erupt following a lengthy period of erosion and volcanic quiescence. During the early alkalic and shield stages, two or more elongate rift zones may develop as flanks of the volcano separate. Mantle-derived magma rises through a vertical conduit and is temporarily stored in a shallow summit reservoir from which magma may erupt within the summit region or be injected laterally into the rift zones. The ongoing activity at Kilauea's Pu?u ?O?o cone that began in January 1983 is one such rift-zone eruption. The rift zones commonly extend deep underwater, producing submarine eruptions of bulbous pillow lava. Once a volcano has grown above sea level, subaerial eruptions produce lava flows of jagged, clinkery ?a?a or smooth, ropy pahoehoe. If the flows reach the ocean they are rapidly quenched by seawater and shatter, producing a steep blanket of unstable volcanic sediment that mantles the upper submarine slopes. Above sea level then, the volcanoes develop the classic shield profile of gentle lava-flow slopes, whereas below sea level slopes are substantially steeper. While the volcanoes grow rapidly during the shield stage, they may also collapse catastrophically, generating giant landslides and tsunami, or fail more gradually, forming slumps. Deformation and seismicity along Kilauea's south flank indicate that slumping is occurring there today. Loading of the underlying Pacific Plate by the growing volcanic edifices causes subsidence, forming deep basins at the base of the volcanoes. Once volcanism wanes and lava flows no longer reach the ocean, the volcano continues to submerge, while erosion incises deep river valleys, such as those on the Island of Kaua?i. The edges of the submarine terraces that ring the islands, thus, mark paleocoastlines that are now as much as 2,000 m underwater, many of which are capped by drowned coral reefs.

Hawai'i↗
USGS1972

Map Showing Areas Containing Swelling Clay in the Morrison Quadrangle, Jefferson County, Colorado

Formations that contain clays having swelling pressures higher than 2,500 pounds per square foot (as measured by the Potential Volume Change meter) are listed in order of decreasing swelling pressure: Denver Formation, Pierre Shale, Laramie Formation, Green Mountain Conglomerate, Fox Hills Sandstone, and Arapahoe Formation. Some landslides derived from these formations also contain swelling clay and are mapped with the bedrock formations listed above.

IMAP↗
USGS1978

Geologic map of the Boulder-Fort Collins-Greeley area, Colorado

This digital map shows the geographic extent of rock stratigraphic units (formations) as compiled by Colton in 1976 under the Front Range Urban Corridor Geology Program. Colton used his own geologic mapping and previously published geologic maps to compile one map having a single classification of geologic units. The resulting published color paper map (USGS Map I-855-G, Colton, 1978) was intended for land-use planning and to depict the regional geology. In 1997-1999, another USGS project designed to address urban growth issues was undertaken. This project, the USGS Front Range Infrastructure Resources Project, undertook to digitize Colton's map at 1:100,000 scale, making it useable in Geographical Information Systems (GIS). That product is described here. In general, the digitized map depicts in its western part Precambrian igneous and metamorphic rocks, Pennsylvanian and younger sedimentary rock units, major faults, and brecciated zones along an eastern strip (5-20 km wide) of the Front Range. The central and eastern parts of the map (Colorado Piedmont) show a mantle of Quaternary unconsolidated deposits and interspersed outcrops of sedimentary rock of Cretaceous or Tertiary age. A surficial mantle of unconsolidated deposits of Quaternary age is differentiated and depicted as eolium (wind-blown sand and silt), alluvium (river gravel, sand, and silt of variable composition), colluvium, and a few landslide deposits. At the mountain front, north-trending, Paleozoic and Mesozoic formations of sandstone, shale, and minor limestone dip mostly eastward and form folds, fault blocks, hogbacks and intervening valleys. Local dikes and sills of Tertiary rhyodacite and basalt intrude rocks near the range front, mostly in the Boulder area.

Colorado↗
USGS1979

Geologic map of the greater Denver area, Front Range urban corridor, Colorado

This digital map shows the areal extent of surficial deposits and rock stratigraphic units (formations) as compiled by Trimble and Machette from 1973 to 1977 and published in 1979 under the Front Range Urban Corridor Geology Program. Trimble and Machette compiled their geologic map from published geologic maps and unpublished geologic mapping having varied map unit schemes. A convenient feature of the compiled map is its uniform classification of geologic units that mostly matches those of companion maps to the north (USGS I-855-G) and to the south (USGS I-857-F). Published as a color paper map, the Trimble and Machette map was intended for land-use planning in the Front Range Urban Corridor. This map recently (1997-1999) was digitized under the USGS Front Range Infrastructure Resources Project. In general, the mountainous areas in the western part of the map exhibit various igneous and metamorphic bedrock units of Precambrian age, major faults, and fault brecciation zones at the east margin (5-20 km wide) of the Front Range. The eastern and central parts of the map (Colorado Piedmont) depict a mantle of unconsolidated deposits of Quaternary age and interspersed outcroppings of Cretaceous or Tertiary-Cretaceous sedimentary bedrock. The Quaternary mantle comprises eolian deposits (quartz sand and silt), alluvium (gravel, sand, and silt of variable composition), colluvium, and a few landslides. At the mountain front, north-trending, dipping Paleozoic and Mesozoic sandstone, shale, and limestone bedrock formations form hogbacks and intervening valleys.

Colorado↗
USGS1987

Subsurface stratigraphy of the eastern Hollister Valley, California

In September 1977, four cores were recovered by shallow auger drilling from Hollister Valley, California, near the Calaveras fault. The wells were drilled to search for evidence that Hollister Valley may have been occupied by a large lake during the late Pleistocene or Holocene. This small valley, near Monterey Bay, may have been dammed by a large landslide on the San Andreas fault (Jenkins, 1973; Herd and Helley, 1977). The cores sampled the first 38 m of sediment below the valley floor, but no lacustrine deposits were found at these sites; a very detailed record to Holocene alluviation in a tectonically subsiding basin.

California↗
USGS1984

Aeromagnetic map of the Fossil Springs Roadless Area, Yavapai, Gila, and Coconino counties, Arizona

The aeromagnetic map of the Fossil Springs Roadless Area was compiled from data collected in 1980 by Airmag Surveys, Inc., for the U.S. Geological Survey. Total magnetic intensity measurements were made along east-west flight lines about 0.5 mi apart and flown at an average altitude of 1,000 ft above the ground surface. A regional magnetic field (the International Geomagnetic Reference Field, 1975, updated to months flown) was removed from the data and a constant of 50,800 gammas was added to the adjusted total field intensity values. The roadless area includes the upper part of Fossil Creek and its northeastern tributaries in Sandrock Canyon and Calf Pen Canyon. The extremely rugged canyon of Fossil Creek is in several places more than 1,500 ft deep. Elevation of the canyon floor ranges from 4,600 ft near the mouth of Calf Pen Canyon to 3,500 ft at the southwest end of the area. Peaks and ridges on the uplands bordering the canyons range in elevation from 5,300 ft west of Fossil Springs to 6,900 ft in the northeastern part of the area. Maximum topographic relief along these uplands is less than 200 ft. The Fossil Springs Roadless Area is underlain by more than 3,000 ft of Paleozoic rocks consisting mostly of sandstone, shale, dolomite, and limestone. West of Fossil Springs and along most of the border of the area, these rocks are generally overlain by late Tertiary volcanic rocks, mainly basaltic lavas and pyroclastic deposits. Quaternary alluvial, colluvial, landslide, and travertine deposits overlie large parts of the country rock in the canyons. In the southwestern part of the area, the volcanic rocks are more than 2,000 ft thick. Along the northwest and northeast margins, these rocks are 300-400 ft thick. The prevailing dip of the Paleozoic strata is low to the north or northeast. The dominant homoclinal structure is interrupted by several fault blocks, in which the strata dip westward or southward. All the faults are high-angle normal faults and have displacements commonly ranging from about 50 to 400 ft. Although fault relations are obscure within the volcanic sequence, many faults seem to displace the volcanic rocks less than the underlying Paleozoic rocks. The volcanic rocks, which rest unconformably on the Paleozoic strata, are flat lying in the northern part of the map area, but west of Fossil Springs they dip gently southwestward. The ancestral Mogollon Rim, a north-northwest-trending escarpment of Paleozoic rocks now concealed by Tertiary volcanic rocks lies near Fossil Springs (Twenter, 1962). The magnetic anomalies and patterns on the aeromagnetic map reflect variations of magnetization in the underlying rocks. Basaltic rocks contain moderate amounts of magnetic minerals, mainly magnetite, and possess strong intensities of magnetization. The more silicic volcanic rocks have much lower magnetization intensities. Sedimentary rocks contain little or no magnetite and are virtually nonmagnetic.

Arizona↗
USGS1984

Types of damage that could result from a great earthquake in the New Madrid, Missouri, seismic zone

In the winter of 1811–1812 a series of three great earthquakes occurred in the New Madrid seismic zone. In addition to the three principal shocks, at least 15 other earthquakes, I o ≥ VIII, occurred within a year of the first large earthquake on December 16, 1811. The three main shocks were felt over the entire eastern United States. They were strong enough to cause minor damage as far away as Indiana and Ohio on the north, the Carolinas on the east, and southern Mississippi on the south. They were strong enough to cause severe or structural damage in parts of Missouri, Illinois, Indiana, Kentucky, Tennessee, Mississippi, and Arkansas. The section of this poster titled "Seismic history of the New Madrid region" describes what happened in the epicentral region. Fortunately, few people lived in the severely shaken area in 1811; that is not the case today. What would happen if a series of earthquakes as large and numerous as the "New Madrid" earthquakes were to occur in the New Madrid seismic zone today? Photographs 1-10 show typical damage to structures that occurred during various earthquakes in the United States. Structural damage to buildings in the Modified Mercalli intensity scale, a scale used for assigning numbers to earthquake effects, begins at intensity VIII. Minor or architectural damage (cracked plaster, windows, and chimneys) occurs at intensities VI and VII, and effects on people and small objects predominate at intensities below VI (earthquake felt, direction and duration noted, dishes broken). Photographs 1-10 illustrate damage caused by intensity VIII and above. None of the damage shown in these photographs occurred in earthquakes larger than the 1811–1812 New Madrid shocks, and most of the examples are from considerably smaller shocks. Photographs 1-4 and 7 show damage to masonry buildings, mostly old and unreinforced, none designed to be earthquake resistant. How many such buildings are in use in your community? Photographs 5 and 6 show damage to modern structures close to the epicenter of a magnitude 6.5 earthquake, a small shock compared to the magnitudes (8.4–8.7) of the New Madrid earthquakes. Photographs 8–10 are typical of damage that can occur at large distances from great earthquakes. Tall buildings are particularly susceptible to ground motions with relatively long periods (greater than 1 second), while short, rigid buildings are generally more likely to be damaged by ground motions with periods of less than 1 second. Shorter period ground motions attenuate more rapidly with distance from the epicenter than do the longer period motions. The 1811-1812 earthquakes produced extensive ground effects. Earthquakes can cause many different kinds of ground effects, ranging from minor fissures, slumps, and rockslides to major landslides and disturbances of the ground surface. Photographs 1117 show typical earthquake ground effects and the kinds of damage they can cause to manmade structures. Is another earthquake as large as the 1811-1812 shocks really likely to occur in New Madrid seismic zone? Great earthquakes such as the 1811-1812 series are estimated to occur in the zone on the average every 500 years. However, earthquakes strong enough to cause structural damage (VIII in the Modified Mercalli intensity scale) are estimated to occur in the seismic zone on the average every 50 years. The last such shock occurred in 1843. How do you prepare for a possible earthquake and what do you do if one occurs? The section on "Earthquake safety tips" explains what to do before, during, and after an earthquake. Want to know more? See "Sources of additional information." Other reports of interest are listed in "References cited."

New Madrid seismic zone↗