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USGS2012

Influence of fault trend, bends, and convergence on shallow structure and geomorphology of the Hosgri strike-slip fault, offshore central California

We mapped an &sim;94-km-long portion of the right-lateral Hosgri fault zone in offshore central California using a dense network of high-resolution seismic reflection profiles, marine magnetic data, and multibeam bathymetry. These data document the location, length, and continuity of multiple fault strands, highlight fault-zone heterogeneity, and demonstrate the importance of fault trend, fault bends, and fault convergence in the development of shallow structure and tectonic geomorphology along strike-slip faults. Eight sections (A through H) of the Hosgri fault are mapped. The fault trends &sim;335° to 341° in the southern &sim;40 km of the study area (sections A through C) where shallow deformation is primarily dilational. The absence of tectonic uplift in this area has contributed to localization of the Santa Maria River and delta and, as a result, Holocene sediments cover the fault zone. The Hosgri fault generally trends 329° to 337° in the central &sim;24 km of the study area (sections D through F), which coincides with oblique convergence of the Hosgri and the more northwest-trending Los Osos and Shoreline faults. This convergence has resulted in local restraining and releasing fault bends, transpressive uplifts, and extensional basins of varying size and morphology. Notably, development of a paired fault bend is linked to indenting and bulging of the Hosgri fault by a strong crustal block translated to the northwest along the Shoreline fault. Two diverging Hosgri fault strands bounding a central uplifted block characterize the northern &sim;30 km of the Hosgri fault (sections G and H) in this area. The eastern Hosgri passes through significant releasing (329° to 335°) and restraining (335° to 328°) bends before passing onland at San Simeon; the releasing bend is the primary control on development of an elongate, asymmetric, 15-km-long × 300- to 2400-m-wide, “Lazy Z” sedimentary basin. The western strand of the Hosgri fault passes through a significant restraining bend (329° to 316°) and continues northward until slip is transferred to faults underlying the Piedras Blancas fold belt. Earthquake hazard assessments should incorporate a minimum rupture length of 110 km based on continuity of the Hosgri fault zone through this area. Lateral slip rates may vary along the fault (both to the north and south) as different structures converge and diverge but are probably in the geodetically estimated range of 2–4 mm/yr.

California↗

USGS2015

How big of an effect do small dams have? Using geomorphological footprints to quantify spatial impact of low-head dams and identify patterns of across-dam variation

Longitudinal connectivity is a fundamental characteristic of rivers that can be disrupted by natural and anthropogenic processes. Dams are significant disruptions to streams. Over 2,000,000 low-head dams (<7.6 m high) fragment United States rivers. Despite potential adverse impacts of these ubiquitous disturbances, the spatial impacts of low-head dams on geomorphology and ecology are largely untested. Progress for research and conservation is impaired by not knowing the magnitude of low-head dam impacts. Based on the geomorphic literature, we refined a methodology that allowed us to quantify the spatial extent of low-head dam impacts (herein dam footprint), assessed variation in dam footprints across low-head dams within a river network, and identified select aspects of the context of this variation. Wetted width, depth, and substrate size distributions upstream and downstream of six low-head dams within the Upper Neosho River, Kansas, United States of America were measured. Total dam footprints averaged 7.9 km (3.0–15.3 km) or 287 wetted widths (136–437 wetted widths). Estimates included both upstream (mean: 6.7 km or 243 wetted widths) and downstream footprints (mean: 1.2 km or 44 wetted widths). Altogether the six low-head dams impacted 47.3 km (about 17%) of the mainstem in the river network. Despite differences in age, size, location, and primary function, the sizes of geomorphic footprints of individual low-head dams in the Upper Neosho river network were relatively similar. The number of upstream dams and distance to upstream dams, but not dam height, affected the spatial extent of dam footprints. In summary, ubiquitous low-head dams individually and cumulatively altered lotic ecosystems. Both characteristics of individual dams and the context of neighboring dams affected low-head dam impacts within the river network. For these reasons, low-head dams require a different, more integrative, approach for research and management than the individualistic approach that has been applied to larger dams.

PLoS ONE↗

USGS2003

Lewis and Clark's observations and measurements of geomorphology and hydrology, and changes with time

Two VERY different men, Meriwether Lewis and William Clark, joined to J, ~ake the first recorded set of scientific observations and measurements of geomorphology and hydrology west of the Mississippi River. They did not limit themselves to these two scientific topics but were true naturalists, making observations and measurements related to astronomy (Large, 1979; Bedini, 1984; Plamondon, 1991; Bergantino, 1998), biology (Cutright, 1969), ecology, ethnology (Ronda, 1984a), geology (Bluemle, 2001; Bergantino, 1998), and phenology, as well as to the general geographical understanding of the arrangements of rivers and other topographical features of the trans-Mississippi West (Allen, 1975) .

Circular↗

USGS2004

Distribution of Holocene Sediment in Chesapeake Bay as Interpreted from Submarine Geomorphology of the Submerged Landforms, Selected Core Holes, Bridge Borings and Seismic Profiles

Overview -- We have interpreted the geomorphology of the submerged landforms to show thick Holocene sediment that accumulated from three different sources during on-going sea level rise that began 10,000 - 12,000 years ago at the end of Pleistocene. We used a variety of subsurface data from the literature and unpublished information to document thicknesses, materials, dates and duration of processes. Although the details of the true extent and thicknesses are unknown, the deposits of different sources have affinity for particular geographic and submerged geomorphic regions of the Chesapeake Bay and its tidal tributaries. During the last Pleistocene glacial event (Wisconsian), the area now occupied by the Chesapeake Bay was exposed, sea level being about 100 m lower than present. The Susquehanna River valley extended beyond the Bay well out on the exposed Atlantic Shelf. The Susquehanna transported glacial outwash from northern Pennsylvania and New York; the glacio-fluvial deposits were graded to the edge of the continental shelf (Colman et al., 1990; Hack, 1957). Other Piedmont and Appalachian Rivers including the Potomac and James Rivers transported large volumes of sediment to confluence with the Susquehanna channel. Locally, across the encompasing coastal plain landscape, intensive headward erosion, gullies, and slope failure, generated extensive debris flows, sheet wash, and terraces of braided alluvial channel deposits. Large volumes of sediment were moved through the river system to the continental shelf. This was accomplished by a cold, wet climate that included much freezing and thawing; steep eroding slopes resulted from the lowering of sea level from the previous high stand (Stage 5e) between glacial events. Across the Delmarva peninsula extensive wind-blown deposits of sand and loess were recycled onto low terraces and uplands from the unvegetated glacio-fluvial sediments moving through the system (Denny et al., 1979). The volume and distribution of sediment eroded and transported from the watershed surrounding the area of the Bay was several orders of magnitude greater than generally observed in transport and storage on the present day landscape.

Open-File Report↗

USGS2007

Quaternary stratigraphy, drainage-basin development, and geomorphology of the Lake Manix basin, Mojave Desert: Guidebook for fall field trip, Friends of the Pleistocene, Pacific Cell, October 4-7, 2007

The 2007 field trip of the Pacific Cell, Friends of the Pleistocene, visited features of the Quaternary geology and geomorphology of the Lake Manix basin in the Mojave Desert. This report is the guidebook for this trip and includes some discussion of relations observable along the road and at various field trip stops. The Mojave River originates in the San Bernardino Mountains and in high-water years flows north and east to its terminus in Silver Lake playa north of Baker, Calif. Along this course, the river passes through or near several basins that were internally drained prior to integration by the Mojave River, including the Victorville, Harper, Manix, and Soda Lake basins. Sediments in the Lake Manix basin record Mojave River discharge and lake fluctuations that began during the middle Pleistocene and continued through most of the late Pleistocene.

California↗

USGS2007

Geomorphology and depositional sub-environments of Assateague Island MD/VA

The U.S. Geological Survey is studying coastal hazards and coastal change to improve our understanding of coastal ecosystems and to develop better capabilities of predicting future coastal change. One approach to understanding the dynamics of coastal systems is to monitor changes in barrier-island sub-environments through time. This involves examining morphological and topographic change at time scales ranging from millennia to years and space scales ranging from tens of kilometers to meters. Of particular interest are the processes that produce those changes and determining whether or not those processes are likely to persist into the future. In these analyses of hazards and change, both natural and anthropogenic influences are considered. Quantifying past magnitudes and rates of coastal change and knowing the principal factors that govern those changes are critical to predicting what changes are likely to occur under different scenarios, such as short-term impacts of extreme storms or long-term impacts of sea-level rise. Assateague Island MD/VA was selected for detailed mapping of barrier island morphology and topography because the island offers a diversity of depositional sub-environments that are representative of other barrier islands along the middle Atlantic coast. The geomorphology and sub-environment map emphasizes the origins of the surficial features and it also serves as a basis for documenting which sub-environments are relatively stable, such as the barrier island core, and those that are highly dynamic, such as the beach and active overwash zones.

Maryland, Virginia↗

USGS2007

Geomorphology and tectonics at the intersection of Silurian and Death Valleys, Southern California - 2005 Guidebook Pacific Cell Friends of the Pleistocene

This publication describes results from new regional and detailed surficial geologic mapping, combined with geomorphologic, geochronologic, and tectonic studies, in Silurian Valley and Death Valley, California. The studies address a long-standing problem, the tectonic and geomorphic evolution of the intersection between three regional tectonic provinces: the eastern California shear zone, the Basin and Range region of southern Nevada and adjacent California, and the eastern Mojave Desert region. The chapters represent work presented on the 2005 Friends of the Pleistocene field trip and meeting as well as the field trip road log.

California↗

USGS2010

Geomorphology and depositional subenvironments of Gulf Islands National Seashore, Mississippi

The U.S. Geological Survey (USGS) is studying coastal hazards and coastal change to improve our understanding of coastal ecosystems and to develop better capabilities of predicting future coastal change. One approach to understanding the dynamics of coastal systems is to monitor changes in barrier-island subenvironments through time. This involves examining morphological and topographic change at temporal scales ranging from millennia to years and spatial scales ranging from tens of kilometers to meters. Of particular interest are the processes that produce those changes and the determination of whether or not those processes are likely to persist into the future. In these analyses of hazards and change, both natural and anthropogenic influences are considered. Quantifying past magnitudes and rates of coastal change and knowing the principal factors that govern those changes are critical to predicting what changes are likely to occur under different scenarios, such as short-term impacts of extreme storms or long-term impacts of sea-level rise. Gulf Islands National Seashore was selected for detailed mapping of barrier-island morphology and topography because the islands offer a diversity of depositional subenvironments and the islands' areas and positions have changed substantially in historical time. The geomorphologic and subenvironmental maps emphasize the processes that formed the surficial features and also serve as a basis for documenting which subenvironments are relatively stable, such as the beach ridge complex, and those which are highly dynamic, such as the beach and active overwash zones. The primary mapping procedures used supervised functions within a Geographic Information System (GIS) that classified depositional subenvironments and features (map units) and delineated boundaries of the features (shapefiles). The GIS classified units on the basis of tonal patterns of a feature in contrast to adjacent features observed on georeferenced aerial photographs. Land elevations from recent lidar surveys served as supplementary data to assist in delineating the map-unit boundaries.

Mississippi↗

USGS2010

Geomorphology and depositional subenvironments of Gulf Islands National Seashore, Perdido Key and Santa Rosa Island, Florida

The U.S. Geological Survey (USGS) is studying coastal hazards and coastal change to improve our understanding of coastal ecosystems and to develop better capabilities of predicting future coastal change. One approach to understanding the dynamics of coastal systems is to monitor changes in barrier-island subenvironments through time. This involves examining morphologic and topographic change at temporal scales ranging from millennia to years and spatial scales ranging from tens of kilometers to meters. Of particular interest are the processes that produce those changes and the determination of whether or not those processes are likely to persist into the future. In these analyses of hazards and change, both natural and anthropogenic influences are considered. Quantifying past magnitudes and rates of coastal change and knowing the principal factors that govern those changes are critical to predicting what changes are likely to occur under different scenarios, such as short-term impacts of extreme storms or long-term impacts of sea-level rise. Gulf Islands National Seashore was selected for detailed mapping of barrier-island morphology and topography because the islands offer a diversity of depositional subenvironments and because island areas and positions have changed substantially in historical time. The geomorphologic and subenvironmental maps emphasize the processes that formed the surficial features and also serve as a basis for documenting which subenvironments are relatively stable, such as the vegetated barrier core, and those which are highly dynamic, such as the beach and inactive overwash zones. The primary mapping procedures were supervised functions within a Geographic Information System (GIS) that were applied to delineate and classify depositional subenvironments and features, collectively referred to as map units. The delineated boundaries of the map units were exported to create one shapefile, and are differentiated by the field "Type" in the associated attribute table. Map units were delineated and classified based on differences in tonal patterns of features in contrast to adjacent features observed on orthophotography. Land elevations from recent lidar surveys served as supplementary data to assist in delineating the map unit boundaries.

Florida↗

USGS2013

Geomorphology and groundwater origin of amphitheater-shaped gullies at Fort Gordon, Georgia, 2010-2012

Seven amphitheater-shaped gullies at valley heads in the northern part of Fort Gordon, Georgia, were identified by personnel from Fort Gordon and the U.S. Geological Survey during a field investigation of environmental contamination near the cantonment area between 2008 and 2010. Between 2010 and 2012, the amphitheater-shaped gullies were photographed, topographic features were surveyed using a global positioning system device, and the extent of erosion was estimated using Light Detection and Ranging imagery. The seven gullies are distributed across a broad area (and most likely are not the only examples) and have a similar geomorphology that includes (1) an amphitheater (semicircular) shaped escarpment at the upgradient end on a plateau of Upper Eocene sands of no readily discernible elevated catchment area or natural surface-water drainage; (2) a narrow, trench-shaped, flat-bottomed incisement of low-permeability marl at the downgradient end; and (3) steep-sided valley walls, some formed by landslides. Surface-water runoff is an unlikely cause for the amphitheater-shaped gullies, because each valley has a relatively small drainage area of sandy terrain even at those gullies that have recently received discharge from stormwater drains. Also, presumed high rates of runoff and gully formation associated with historic land uses, such as clearcutting, cotton production, and silviculture, would have occurred no later than when the fort was established in the early 1900s. The lack of an elevated catchment area at the headward scarps, the amphitheater shape, and presence of low permeability marl at the base of each feature provides the most convincing lines of evidence for headward erosion by groundwater sapping. The absence of current (2013) seeps and springs at most of the amphitheater-shaped gullies indicates that the gullies may have been formed previously by groundwater sapping under conditions of higher and (or) sustained precipitation amounts, local water-table altitudes, and seepage than current (2013) conditions. One gully characterized by groundwater seepage may support a unique ecological niche that, if assessed to contain endangered species or rare plants, could require protection under State laws.

Georgia↗

USGS2025

Benthic habitat map of Olowalu Reef, Maui, Hawaii—Geomorphological structure, biological cover, and geologic zonation determined with spectral, lidar, and acoustic data

The fringing coral reef off Olowalu, Maui, Hawaii, has been identified as a local conservation priority site. In 2007, the National Oceanic and Atmospheric Administration (NOAA) produced a benthic habitat map of the Hawaiian Islands that was used as a foundation for this study. To support place-based management of the reef in the future, the U.S. Geological Survey (USGS) mapped the geologic zone, major and dominant geomorphological structure, biological cover type, and percent of biological cover for 11 square kilometers (km 2 ) of Olowalu Reef at a minimum mapping unit (MMU) of 100 square meters (m 2 ) to create a benthic habitat map. Heads-up digitization was employed on 0.50-meter (m) natural color satellite orthoimagery with ancillary 1-m acoustic backscatter imagery from single-scan sonar (sound navigation and ranging). A 1-m, 4-m, and 8-m digital bathymetric model (DBM) was interpolated from bathymetric lidar (light detection and ranging), and various geomorphometric layers derived from the DBMs were used for habitat interpretation. Still-frame imagery of the seafloor extracted from vessel-towed underwater video transects on Olowalu Reef served as ground validation points ( n =870) during active mapping and accuracy assessment points ( n =216) for thematic accuracy assessment. Thematic accuracy was cross-validated by the Hawai‘i Department of Land and Natural Resources Division of Aquatic Resources. Final thematic accuracy was 88.8 percent for major structure, 85.6 percent for dominant structure, 86.0 percent for major biological cover, and 78.6 percent for type and percent of major biological cover. Reef and hardbottom constituted 52 percent of the total mapped habitat, comprising mostly aggregate reef (31 percent) and pavement (11 percent), with large swaths of spur-and-groove (9 percent). Of this hardbottom, 17 percent was covered with moderate (10 to <50 percent) coral and 27 percent with high coral cover (50 to <90 percent). High (50 to <90 percent) macroalgae cover dominated the continuous sand sheets in offshore bank/shelf zones. The map created in this study supplements the NOAA 2007 map and expands on the observations made by USGS sampling of the reef. The NOAA 2007 map and our map differed in total areal extent by a negligible 6 m 2 and were in general thematic agreement. Our map is intended to serve as a baseline for public access, general research, local-level management, and reef change for future studies.

Hawaii↗

USGS1987

Geomorphological interpretations of late Quaternary terraces in western Tennessee and their regional tectonic implications

By use of large-scale topographic maps and traditional techniques of geomorphology. a series of stream terraces was identified and delineated on the Obion, Forked Deer, Hatchie, Loosahatchie, and Wolf Rivers in western Tennessee. From lowest and youngest to highest and oldest, they are designated the Finley, Hatchie, Humboldt, and Henderson terraces. The areal extent and continuity of the relict flood plains are ample to permit reconstruction of former elevations and valley slopes. Downvalley gradients of the terraces and morphology are strongly indicative of the processes and events that influenced terrace formation. Nil gradients for several tens of kilometers upstream from the Mississippi alluvial valley on the Finley and Hatchie terraces and shoreline features on the Finley terrace are interpreted as evidence that backwater flooding from the Mississippi Valley produced extensive seasonal or permanent lakes in the tributary valleys. Therefore, in part. these terraces are relict lacustrine plains. The Humboldt and Henderson terraces do not have any of these characteristics and are interpreted as being entirely of fluvial origin. All terraces are capped by a veneer of loess representing one or more episodes of deposition. Interstream terrace correlations made by using only geomorphic evidence are not definitive, and two interpretations are nearly equally viable. One of these has potentially significant regional tectonic implications because it suggests Quaternary uplift in the vicinity of a known pluton along the flank of the major rift in the New Madrid seismic zone. However, the preferred interpretation suggests that no appreciable regional structural deformation has taken place. Neither interpretation indicates Quaternary deformation in the upland area relative to the Mississippi alluvial valley. Topographic relationships of the terraces to features resulting from the sequence of Pleistocene aggradation and degradation in the Mississippi Valley indicate correlation of the Finley terrace with the early Wisconsinan episode of outwash deposition. Several lines of evidence suggest correlation of the Hatchie terrace with the Prairie terrace of the lower Mississippi Valley, which is Sangamonian in age. By inference, the Humboldt terrace could be of Yarmouthian age.

Tennessee↗

USGS1956

Surficial geology and geomorphology of Potter County, Pennsylvania

Potter County is located in the Appalachian Plateaus of north-central Pennsylvania and contains the headwaters of the Genesee River, the Allegheny River, and the Susquehanna River. Drift of Wisconsin age covers the northeastern part of the county. This study includes a detailed survev of the surficial deposits of the Genesee quadrangle in north-central Potter County and a reconnaissance of the remainder of the county; a soil survey and a botanical survey were carried on concurrently. The region is a deeply dissected plateau having extensive areas of steeply sloping land separated by narrow ridges and valleys; there is very little level land. Near the junction of the three watersheds the uplands rise to altitudes of more than 2,500 feet. The maximum relief in the Susquehanna drainage is more than 1,500 feet; in the Genesee and Allegheny drainage it. is about 800 feet. Valley walls are steep (15° to 30°), and the uplands have gentle slopes (0.5° to 10°). The drainage pattern is trellised. The climate is continental. Temperatures range from about -30° F. to more than 100° F. The average annual precipitation ranges approximately from 34 to 42 inches. Floods may occur at any season of the year. The large volumes of water from rain or melting snow carried by small streams come from springs. There is little precise data on frost in the ground, but it is probable that the ground seldom freezes in forested areas. The soils of Potter County have relatively immature profiles with poorly developed horizons that commonly have many characteristics inherited from their parent materials. At the great soil group level, the zonal soils are divided into Podzol soils and Brown Podzolic soils. Many soils have a high silt content in the upper part of the profile, apparently derived (at least partly) from a mantle of eolian silt. Mos~ of Potter County is covered by second-growth forests consisting of 40- to 60-year-old hardwood stands. The present forests growing on slopes and summits are composed approximately of 25 species of trees. The northern hardwood region includes most of the county, with an oak-forest region near the borders, principally along its southern margin. Potter County is underlain by sandstone, siltstone, shale, conglomerate, and minor amounts of coal and calcareous rock that range in age from Late Devonian to Pennsylvanian. These rocks form broad open folds that strike northeast. South of the border of the Wisconsin drift, and possibly at two localities inside the drift border, are scattered remnants of ancient soils (here called paleosol), that were formed in preWisconsin time-probably during the Sangamon interglacial stage. This paleosol ranges in texture from clay loam to silt loam, ranges in color from yellowish red to red, includes a few percent to more than 25 percent of rock fragments, and apparently contains a small percentage of gibbsite and varying amounts of kaolinite. Known thicknesses range from 1 to 33 feet. Paleosol was developed on diverse kinds of parent material, such as till, stratified drift, colluvium, and residuum, at altitudes ranging from a few hundred to 2,400 feet. The climatic conditions under which the paleosol formed are uncertain; however, these ancient soils may record an episode of subtropical climatic conditions during which lateritic soils were formed. Perhaps these soils are analogous to the Red-Yellow Podzolic soils of southeastern United States. Except for one possible remnant, no pre-Wisconsin drift has been recognized in Potter County. The Wisconsin glacial deposits of Potter County belong to either the Iowan or Tazewell substages and are dominantly till with minor amounts of glaciofluvial deposits. Erratics of igneous or metamorphic rock comprise less than 0.1 percent of the total number of rock fragments. The till is slightly weathered to depths ranging from 3 to about 12 feet. The drift border is indefinite and has been drawn at the southern limit of erratics or well-rounded or striated pebbles and is only locally marked by a terminal moraine or by a distinct change in the surficial deposits. The drift border is relatively straight and crosses the Genesee quadrangle in a northwesterly direction with little regard for the major topographic features, thus suggesting that the Wisconsin ice sheet had a relatively straight and steep front. Over most of the unglaciated part of Potter County, the bedrock is concealed beneath rubble that probably was formed during the Iowan or Tazewell substage, almost contemporaneously with the adjacent drift. In general, the rubble is thickest and most extensive within about 10 miles of the drift border, becoming thinner and less continuous farther away. The apparent parallelism between a belt of thick periglacial deposits and the drift border suggests that the deposits result from climatic factors in operation while the Wisconsin ice sheet was nearby. Ancient soil structures or patterned ground occur at, or near, the surface of both the periglacial deposits and the adjacent drift. These ancient soil structures are so similar to modern forms in arctic or alpine environments that they are considered to be the result of vigorous frost action. Many of the structures are believed to be a result of down-slope movement of debris by solifluction, facilitated by a frozen subsoil as much as 10 feet deep. Perennially frozen ground may have been present, but this is not a prerequisite. The periglacial deposits underlie long smooth slopes that extend from ridge crest to valley bottom. Flood plains are absent near the headwaters of many streams, the valley walls forming a V-shaped profile. While frost action was in progress, forests probably were restricted to flood plains, lower slopes, and scattered upland areas. Large parts of the upland were bare or partly covered by tundra vegetation; elsewhere, there were scattered trees but no dense forest. 1 2 SURFICIAL GEOLOGY AND GEOMORPHOLOGY OF POTTER COUNTY, PENNSYLVANIA Recent alluvium and alluvial fans include sand and sandy loams, 1 to 3 feet thick, that overlie gravel. The alluvium contains organic matter and lenses of finer materials. Thickness ranges from a few to more than 100 feet. Along the principal streams the alluvium probably overlies Pleistocene deposits. Most of the alluvial fans are composed of unstratified rubbly, pebbly, cobbly. or bouldery sandy loams to silty clay loams with local lenses of stratified sand and gravel. The alluvial fans mapped in the Genesee quadrangle probably include both Wisconsin stage and Recent deposits. The summits of the A.ppalachian Plateaus in north-central Pennsylvania have long been recognized as the remnants or traces of one or more peneplains. To test this hypothesis, a restored contour map was prepared to show the configuration of a supposed peneplain on the assumption that the plateau tops are remnants of such an old erosion surface. The restored contours delineate a surface that corresponds roughly to rock structure. In general, the uplands slope parallel to the dip of the bedrock. The major streams, such as the West Branch Susquehanna River, cross the ridges and valleys of the restored surface in such a way that it is difficult to suppose that the restored surface was ever graded to these streams. On the contrary, it is probable that the restored surface never existed and that the plateau tops are structurally controlled surfaces held up by sandstone and conglomerate beds in the Pottsville and Pocono formations. The plateau tops may have been lowered by erosion as much as 200 feet during the Pleistocene-in other words, after the major streams were incised. If this portion of the Appalachian Plateaus was ever reduced to a peneplain, such a hypothetical surface must have lain many hundreds of feet above the uplands of the present day. The only alternative that might involve peneplanation is the improbable hypothesis that the plateau tops are remnants of a slightly deformed peneplain and that the peneplain was folded along the axes of the Appalachian orogeny. This remote possibility is not supported by any known evidence. The geomorphic analysis yields no new data on the origin of the cross-axial drainage. Regardless of whether the plateaus are peneplain remnants or are structurally controlled surfaces, the beginning of the major southeastward-flowing streams long antedates the existing landscape. The geomorphic history of Potter County begins with an assumed long interval of erosion during the Mesozoic and early Cenozoic eras, for which no record remains in this area. The southeast master drainage was established by the latter part of the Tertiary period (perhaps at a much earlier date), probably as the result of the northwestward migration of the Atlanticinterior divide. In late Pliocene(?) time, areas adjacent to parts of the West Branch Susquehanna River-and probably elsewhere-had a moderate relief ranging from 300 to 700 feet. Some segments of the West Branch meandered across a broad valley that lay about 900 feet above the present streams. The landscape probably was covered by deep residual soils, perhaps by saprolite. The early Pleistocene history of Potter County is essentially unknown. No deposits of the Kansan stage are known except for a possible trace of pre-Illinoian drift on the uplands in central Potter County (Ayers Hill quadrangle). Some deposits in central and eastern Pennsylvania may be of Kansan age. It is probable that the assumed Aftonian regolith was removed by mass movements and other processes during the Kansan stage, thus resulting in a lowering of the plateau tops by as much as 10 feet. By the close of the Yarmouth(?) interglacial stage the major streams were incised to essentially their present depths. The climates of the Yarmouth interglacial stage probably produced deep residual soils over the landscape, parts of which may still be preserved in the paleosol remnants of the present day. No Illinoian drift is known in Potter County, but drift assigned to this stage occurs in areas to the northwest and to the southeast. Some valleys, such as Kettle Creek valley, were filled with sand and gravel alluvium to depths of as much as 150 feet above their present flood plains. It is assumed that the Yarmouth residual soils were removed by mass movements and other processes induced by a periglacial climate, thus lowering the plateau tops by as much as 10 feet. During the Sangamon interglacial stage, deep (10-to-20 foot) residual soils or paleosol were developed in Potter County and probably throughout much of Pennsylvania, perhaps as a result of lateritic weathering in a subtropical climate. It is possible that the paleosol was largely removed by mass movements and by running water during late Sangamon time. During either the Iowan or Tazewell substages of the Wisconsin (perhaps the Iowan), the ice sheet advanced into the northeastern part of Potter County. The drift is similar to the Olean drift (local usage). The paleosol was almost completely removed by mass movements and other processes induced· by a periglacial climate, prior to drift deposition. This removal probably resulted in a lowering of the plateau tops by as much as 10 feet since Sangamon time. Nearly contemporaneously with drift deposition, the periglacial deposits were formed by frost heaving, solifluction, and fluvial transport in areas outside the drift border. Soil structures or patterned ground were developed on both the drift and the periglacial deposits. It is probable that the forests in the periglacial area were greatly restricted and that large areas on the uplands were essentially treeless. Little is known about the history of Potter County in postOlean time. Presumably, forests completely covered the county by the onset of the next substage, during which the Binghamton drift of MacClintock and Apfel was deposited. This drift also is found in southern New York State. The formation of the alluvium and alluvial fans probably began in the Tazewell substage and continued during the Recent epoch. Since these deposits were formed there has been very little dissection. There is little, if any, difference between soils developed on periglacial deposits and soils developed on drift. The roots of fallen trees have disturbed the soil horizons, and it is unlikely that the existing soil profiles are more than 500 years old. The forested landscape of Potter County has a distinctive microrelief ranging from a few inches to a few feet of mounds and pits produced by the roots of fallen trees. Most mounds and pits range from 10 to 20 feet in length and from 6 to 15 feet in width. On level land, many mounds are oriented with their long axes trending northward, and in some areas the orientation is random. On slopes, the mounds are oriented with their long axes at right angles to the maximum slope as a result of trees falling downslope. The toppling of trees increases the permeability of surficial deposits and mixes and destroys the soil horizons. The microrelief is a factor in forest development. The toppling of trees on slopes is a significant agent of slope erosion. The process loosens, breaks up, or overturns the upper 2 to 3 feet of the forest soil, and it tends to make the surficial layer more stony and to produce features resembling soil structures.

Pennsylvania↗

USGS2015

Offshore geology and geomorphology from Point Piedras Blancas to Pismo Beach, San Luis Obispo County, California

Marine geology and geomorphology were mapped along the continental shelf and upper slope between Point Piedras Blancas and Pismo Beach, California. The map area is divided into the following three (smaller) map areas, listed from north to south: San Simeon, Morro Bay, and Point San Luis. Each smaller map area consists of a geologic map and the corresponding geophysical data that support the geologic mapping. Each geophysical data sheet includes shaded-relief multibeam bathymetry, seismic-reflection-survey tracklines, and residual magnetic anomalies, as well as a smaller version of the geologic map for reference. Offshore geologic units were delineated on the basis of integrated analysis of adjacent onshore geology, seafloor-sediment and rock samples, multibeam bathymetry and backscatter imagery, magnetic data, and high-resolution seismic-reflection profiles. Although the geologic maps are presented here at 1:35,000 scale, map interpretation was conducted at scales of between 1:6,000 and 1:12,000. Sea level was approximately 120 to 130 m lower during the Last Glacial Maximum (about 21 ka). This approximate depth corresponds to the modern shelf break, a lateral change from the gently dipping (0.8° to 1.0°) outer shelf to the slightly more steeply dipping (about 1.5° to 2.5°) upper slope in the central and northern parts of the map area. South of Point San Luis in San Luis Bay, deltaic deposits offshore of the mouth of the Santa Maria River (11 km south of the map area) have prograded across the shelf break and now form a continuous low-angle (about 0.8°) ramp that extends to water depths of more than 160 m. The shelf break defines the landward boundary of slope deposits. North of Estero Bay, the shelf break is characterized by a distinctly sharp slope break that is mapped as a landslide headscarp above landslide deposits. Multibeam imagery and seismic-reflection profiles across this part of the shelf break show evidence of slope failure, such as slumping, sliding, and soft-sediment deformation, along the entire length of the scarp. Notably, this shelf-break scarp corresponds to a west splay of the Hosgri Fault that dies out just north of the scarp, suggesting that faulting is controlling the location (and instability) of the shelf break in this area.

California↗

USGS2008

Questa baseline and pre-mining ground-water quality investigation. 17. Geomorphology of the Red River Valley, Taos County, New Mexico, and influence on ground-water flow in the shallow alluvial aquifer

In April 2001, the U.S. Geological Survey (USGS) and the New Mexico Environment Department (NMED) began a cooperative study to infer the pre-mining ground-water chemistry at the Molycorp molybdenum mine site in the Red River Valley of north-central New Mexico. This report is one in a series of reports that can be used to determine pre-mining ground-water conditions at the mine site. Molycorp’s Questa molybdenum mine in the Red River Valley, northern New Mexico, is located near the margin of the Questa caldera in a highly mineralized region. The bedrock of the Taos Range surrounding the Red River is composed of Proterozoic rocks of various types, which are intruded and overlain by Oligocene volcanic rocks associated with the Questa caldera. Locally, these rocks were altered by hydrothermal activity. The alteration zones that contain sulfide minerals are particularly important because they constitute the commercial ore bodies of the region and, where exposed to weathering, form sites of rapid erosion referred to as alteration scars. Over the past thousand years, if not over the entire Holocene, erosion rates were spatially variable. Forested hillslopes eroded at about 0.04 millimeter per year, whereas alteration scars eroded at about 2.7 millimeters per year. The erosion rate of the alteration scars is unusually rapid for naturally occurring sites that have not been disturbed by humans. Watersheds containing large alteration scars delivered more sediment to the Red River Valley than the Red River could remove. Consequently, large debris fans, as much as 80 meters thick, developed within the valley. The geomorphology of the Red River Valley has had several large influences on the hydrology of the shallow alluvial aquifer, and those influences were in effect before the onset of mining within the watershed. Several reaches where alluvial ground water emerges to become Red River streamflow were observed by a tracer dilution study conducted in 2001. The aquifer narrows where erosion-resistant bedrock, which tends to form vertical cliffs, restricts the width of the valley bottom. Although the presence of a shallow bedrock sill, overlain by shallow alluvium, is a plausible cause of ground-water emergence, this cause was not demonstrated in the study area. The water-table gradient can locally decrease in the downstream direction because of changes in the hydraulic properties of the alluvium, and this may be a contributing cause of ground-water emergence. However, at one site (near Cabin Springs), ground-water emergence could not be explained by spatial changes in geometric or hydraulic properties of the aquifer. Furthermore, the available evidence demonstrates that ground water flowing through bedrock fractures or colluvium entered the north side of the alluvial aquifer, and is the cause of ground-water emergence. At that location the alluvial aquifer was already flowing full, causing the excess water to emerge into the stream. An indirect consequence of altered rock in the tributary watersheds is the rapid erosion rate of alteration scars combined with the hydraulic properties of sediments shed from those scars. Where alteration scars are large the debris fans at the mouths of the tributary watersheds substantially encroach into the Red River Valley. At such locations debris-fan materials dominate the width and thickness of the alluvium in the valley and reduce the rate of flow of ground water within the Red River alluvial aquifer. Most sites of groundwater emergence are located immediately upstream from or along the margins of debris fans. A substantial fraction of the ground water approaching a debris fan can emerge to become streamflow. This last observation has three implications. First, very little water can flow the entire length of the study area entirely within the alluvial aquifer because the ground water repeatedly contacts debris-fan sediments over that length. Second, it follows that emerging water containing unique elemental constituents must have entered the alluvial aquifer at a relatively short distance upstream. Third, a gravel aquifer downstream from a large debris fan can transmit more ground water than flows into it through the debris fan. This observation explains how the water table can be naturally, and permanently, located well beneath the level of the bed of a perennial stream.

New Mexico↗

USGS2007

An Assessment of Hydrology, Fluvial Geomorphology, and Stream Ecology in the Cardwell Branch Watershed, Nebraska, 2003-04

An assessment of the 16.3-square-mile Cardwell Branch watershed characterized the hydrology, fluvial geomorphology, and stream ecology in 2003-04. The study - performed by the U.S. Geological Survey in cooperation with the City of Lincoln, Nebraska, and the Lower Platte South Natural Resources District - focused on the 7.7-square-mile drainage downstream from Yankee Hill Reservoir. Hydrologic and hydraulic models were developed using the Hydrologic Modeling System (HEC-HMS) and River Analysis System (HEC-RAS) of the U.S. Army Corps of Engineers Hydraulic Engineering Center. Estimates of streamflow and water-surface elevation were simulated for 24-hour-duration design rainstorms ranging from a 50-percent frequency to a 0.2-percent frequency. An initial HEC-HMS model was developed using the standardized parameter estimation techniques associated with the Soil Conservation Service curve number technique. An adjusted HEC-HMS model also was developed in which parameters were adjusted in order for the model output to better correspond to peak streamflows estimated from regional regression equations. Comparisons of peak streamflow from the two HEC-HMS models indicate that the initial HEC-HMS model may better agree with the regional regression equations for higher frequency storms, and the adjusted HEC-HMS model may perform more closely to regional regression equations for larger, rarer events. However, a lack of observed streamflow data, coupled with conflicting results from regional regression equations and local high-water marks, introduced considerable uncertainty into the model simulations. Using the HEC-RAS model to estimate water-surface elevations associated with the peak streamflow, the adjusted HEC-HMS model produced average increases in water-surface elevation of 0.2, 1.1, and 1.4 feet for the 50-, 1-, and 0.2-percent-frequency rainstorms, respectively, when compared to the initial HEC-HMS model. Cross-sectional surveys and field assessments conducted between November 2003 and March 2004 indicated that Cardwell Branch and its unnamed tributary appear to be undergoing incision (the process of downcutting) (with three locations showing 2 or more feet of streambed incision since 1978) that is somewhat moderated by the presence of grade controls and vegetation along the channel profile. Although streambank failures were commonly observed, 96 percent of the surveyed cross sections were classified as stable by planar and rotational failure analysis-a disconnect that may have been the result of assumed soil properties. Two process-based classification systems each indicated that the reaches within the study area were incising and widening, and the Rosgen classification system characterized the streams as either type E6 or B6c. E6 channels are hydraulically efficient with low width-depth ratios, low to moderate sinuosity, and gentle to moderately steep slopes. B6c channels typically are incised with low width-depth ratios maintained by riparian vegetation, low bedload transport, and high washload transport. No obvious nickpoints (interruption or break in slope) were observed in the thalweg profile (line of maximum streambed descent), and the most acute incision occurred immediately downstream from bridges and culverts. Nine water-quality samples were collected between August 2003 and November 2004 near the mouth of the watershed. Sediment-laden rainfall-runoff substantially affected the water quality in Cardwell Branch, leading to greater biochemical and chemical oxygen demands as well as increased concentrations of several nutrient, bacteriological, sediment, and pesticide constituents. The storage of rainfall runoff in Yankee Hill Reservoir may prolong the presence of runoff-related constituents downstream. Across the study area, there was a lack of habitat availability for aquatic biota because of low dissolved oxygen levels and low streamflows or dry channels. In August 2003, the aquatic community near the mouth of

Scientific Investigations Report↗

USGS2011

Geomorphology of the Elwha River and its Delta: Chapter 3 in Coastal habitats of the Elwha River, Washington--biological and physical patterns and processes prior to dam removal

The removal of two dams on the Elwha River will introduce massive volumes of sediment to the river, and this increase in sediment supply in the river will likely modify the shapes and forms of the river and coastal landscape downstream of the dams. This chapter provides the geologic and geomorphologic background of the Olympic Peninsula and the Elwha River with emphasis on the present river and shoreline. The Elwha River watershed was formed through the uplift of the Olympic Mountains, erosion and movement of sediment throughout the watershed from glaciers, and downslope movement of sediment from gravitational and hydrologic forces. Recent alterations to the river morphology and sediment movement through the river include the two large dams slated to be removed in 2011, but also include repeated bulldozing of channel boundaries, construction and maintenance of flood plain levees, a weir and diversion channel for water supply purposes, and engineered log jams to help enhance river habitat for salmon. The shoreline of the Elwha River delta has changed in location by several kilometers during the past 14,000 years, in response to variations in the local sea-level of approximately 150 meters. Erosion of the shoreline has accelerated during the past 80 years, resulting in landward movement of the beach by more than 200 meters near the river mouth, net reduction in the area of coastal wetlands, and the development of an armored low-tide terrace of the beach consisting primarily of cobble. Changes to the river and coastal morphology during and following dam removal may be substantial, and consistent, long-term monitoring of these systems will be needed to characterize the effects of the dam removal project.

Washington↗

USGS1995

Application of surface geophysical techniques in a study of the geomorphology of the lower Copper River, Alaska

As part of a geomorphology study of the lower Copper River, three surface geophysical techniques were tested for their ability to detect infilled scour holes at bridge piers, old river channels, and subbottom deposits in a glacier-formed lake. The methods were (1) ground-penetrating radar, (2) continuous seismic reflection using a color fathometer, and (3) continuous seismic reflection using a tuned transducer. In water depths less than 20 feet, ground-penetrating radar detected infilled scour holes at bridge piers and old river channels on land. Continuous seismic reflection using a tuned transducer was effective in water and detected infilled scour holes at bridge piers and subbottom deposits in a glacier lake. The color fathometer was useful in determining depths of water but was not able to penetrate the subbottom.

Water-Resources Investigations Report↗