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Elliptical borehole enlargements or "breakouts" caused by systematic spalling of a borehole wall due to regional maximum horizontal stresses were identified in 18 wells drilled in the Coast Range and Willamette ...
Citation Citation
- Title:
- I. Direction of maximum horizontal compression in western Oregon determined by borehole breakouts. II. Structure and tectonics of the northern Willamette Valley, Oregon
- Author:
- Werner, Kenneth Stefan
Elliptical borehole enlargements or "breakouts" caused by systematic spalling of a borehole wall due to regional maximum horizontal stresses were identified in 18 wells drilled in the Coast Range and Willamette Valley of western Oregon. The breakouts generally indicate a NNW to NNE orientation of maximum horizontal compression (oH[subscript max]) that agrees with the predominant direction of Gllmax determined from earthquake focal mechanisms, from post-middle Miocene structural features, and from alignments of Holocene volcanic centers in the Pacific Northwest. However, this orientation is inconsistent with the N50°E convergence between the Juan de Fuca and North American plates determined by Riddihough [1984] from Juan de Fuca plate magnetic lineations as young as 730 ka (the Brunhes-Matuyama boundary). The predominant NNW to NNE orientation of Gllmax may be due to the complex interaction of a northwestward-moving Pacific plate driving into the Gorda and Juan de Fuca plates and indirectly transmitting N-S compression across the strongly coupled Cascadia subduction zone into the overriding North American plate [Spence, 1989]. Alternatively, the predominant NNW to NNE orientation of cillmax may be due to a landward counterclockwise rotation of the direction of oHmax from N50°E compression offshore to N-S compression in the Coast Range. The northern Willamette Valley lies on the eastern flank of the broad northnortheast- trending Oregon Coast Range structural arch. Eocene to Oligocene marine sedimentary rocks crop out along the western side of the northern Willamette Valley and form a gently eastward dipping homocline. However, beneath the center of the Willamette Valley, Eocene to Oligocene strata are structurally warped up. During the Eocene several major volcanic centers subdivided the Coast Range forearc region into shallow to deep marine basins. Several such volcanic centers occur adjacent to the northern Willamette Valley and are associated with residual gravity anomaly highs and lineations. The top of basalt in the northern Willamette Valley (middle Miocene Columbia River basalt except near the valley margins) is contoured based on petroleum exploration wells, water wells, and seismic-reflection data. It is structurally downwarped to an altitude of less than -500 m just north of Woodburn. The downwarp is bounded to the south by the NE-trending Waldo Hills range-front fault and in part to the north by the NE-trending Yamhill River-Sherwood fault zone. The NW-trending Mt. Angel fault extends across the northern Willamette Valley between Mt. Angel and Woodburn and deforms middle Miocene Columbia River basalt and overlying Pliocene and Miocene fluvial and lacustrine deposits. The top of Columbia River basalt is vertically separated, NE side up, roughly 100 m based on seismic-reflection data near Woodburn, and 250+ m based on water-well data near Mt. Angel. The Mt. Angel fault is part of a NW-trending structural zone that includes the Gales Creek fault west of the Tualatin basin; however, a connection between the Gales Creek and Mt. Angel faults does not occur through Willamette River alluvial deposits. A series of small earthquakes (6 events with me = 2.0, 2.5, 2.4, 2.2, 2.4, 1.4) occurred on August 14, 22, and 23, 1990 with epicenters near the northwest end of the Mt. Angel fault. Routine locations indicate a depth of about 30 km. The preferred composite focal mechanism is a right-lateral strike-slip fault with a small normal component on a plane striking north and dipping steeply to the west. Both recent mapping of the Mt. Angel fault and the recent seismicity suggest that the Gales Creek-Mt. Angel lineament is similar to the Portland Hills-Clackamas River lineament found to the north. Together, these two lineaments may take up right-lateral strike-slip motions imposed on the upper plate by oblique subduction. Boring Lava appears to occur extensively in the subsurface of the northeastern portion of the northern Willamette Valley based on seismic data. Many of the faults in the area are interpreted to be largely caused by doming from influx of Boring magma or subsidence associated with evacuation of Boring magma. Such faults occur at Petes Mountain, at Parrett Mountain, along the Molalla River, and possibly near Curtis. The fault along the Molalla River appears to offset the Pleistocene (?) Rowland Formation 1 m (Glenn, 1965).
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This thesis develops a manual for interpreters at six National Park Service areas established to preserve and interpret fossils of the Cenozoic Era: Fossil Butte National Monument (Wyoming), John Day Fossil ...
Citation Citation
- Title:
- Changing landscape, climate, and life during the age of mammals: interpreting paleontology, evolving ecosystems, and climate change in the Cenozoic fossil parks
- Author:
- Kenworthy, Jason P.
This thesis develops a manual for interpreters at six National Park Service areas established to preserve and interpret fossils of the Cenozoic Era: Fossil Butte National Monument (Wyoming), John Day Fossil Beds National Monument (Oregon), Badlands National Park (South Dakota), Florissant Fossil Beds National Monument (Colorado), Agate Fossil Beds National Monument (Nebraska), and Hagerman Fossil Beds National Monument (Idaho). The manual will help interpreters place their park’s story into the context of three components of paleoecosystems preserved in each park: changes in geologic landscapes, global climate, and the evolution of mammals. It also provides context for interpreting modern climate change. The colorful landscapes of the Cenozoic fossil parks preserve evidence of changing landscapes, climates, and life as well as clues about change affecting our future. Because the six parks are nationally and globally significant paleontological sites, they also offer interpretive opportunities to connect visitors to the science of paleontology. The manual is written for interpreters with a variety of geology, other science and humanities backgrounds. The first three chapters provide a basic foundation of paleontological knowledge and interpretive resources applicable to all of the parks. Chapter 1 is an introduction to the scope and significance of the fossils and paleoecosystems preserved in each of the Cenozoic fossil parks. Chapter 2 outlines NPS interpretive theory and offers practical information for developing paleontology interpretation and interpreting longterm paleoecosystem evolution. Chapter 3 provides geologic content and interpretive methods for answering three common questions visitors ask: How old are these fossils? What is a fossil? and Were all these fossils found here? Interpretive responses to these questions allow visitors to connect with the Cenozoic Era, fossilization processes, and the profound sense of place afforded by the fossil parks. Chapters 4, 5, and 6 summarize how the major components of ecosystems changed between the extinction of dinosaurs 65 million years ago and the beginning of the Pleistocene “ice ages” 2.6 million years ago. Chapter 4 details the active geologic processes—mountain building and volcanic activity—of the American West during this time period and how these processes helped form and preserve the paleoecosystems of the parks. Chapter 5 places the parks’ paleoecosystems in chronological order and relates them to the global climate transition from the “greenhouse” world (nearly-tropical forests and lakes at Fossil Butte NM, John Day Fossil Beds NM, Badlands NP, and Florissant Fossil Beds NM) of 65 to 34 million years ago, to the “icehouse” world (cooler and drier woodlands, savannahs, and grasslands at John Day Fossil Beds NM, Badlands NP, Agate Fossil Beds NM, and Hagerman Fossil Beds NM) beginning 34 million years ago and continuing today. Chapter 6 traces the evolution of the horse during this time of global change from a four-toed, dog-sized browser to a hoofed, zebra-sized grazer on the grasslands of the American West. Chapter 7 describes the “ice ages” that followed the stories of the Cenozoic fossil parks. It also places the global climatic and ecosystem changes told by the Cenozoic fossil parks in the context of modern, rapid, anthropogenic climate changes. Each chapter includes “Digging Deeper” boxes that provide more detailed geologic content, or interpretive suggestions.
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173. [Article] Fault behavior over geomorphic time scales in the Pakistan Himalaya, Kashmir Himalaya, and California
The state of the knowledge for fault behavior in the northwest Himalaya and California varies dramatically. In the Pakistan and Kashmir Himalaya, few data constrain the role that individual active faults ...Citation Citation
- Title:
- Fault behavior over geomorphic time scales in the Pakistan Himalaya, Kashmir Himalaya, and California
- Author:
- Madugo, Christopher Lee Madden
The state of the knowledge for fault behavior in the northwest Himalaya and California varies dramatically. In the Pakistan and Kashmir Himalaya, few data constrain the role that individual active faults play in accommodating Indo-Eurasian convergence and the relative earthquake hazard across the region. By contrast, the San Andreas fault in California is one of the best-studied fault systems in the world, although seismic hazard models have yet to incorporate certain available geologic data, such as measurements of slip-in-the-last-event. This dissertation addresses the sparsity of earthquake hazard data in the northwest Himalaya, and the problem of how best to utilize available data in hazard models for California by (1) Providing the first quantitative constraints on the latest Pleistocene slip rate and earthquake potential for the thrust front Pakistan; (2) Characterizing the rate and style of upper plate faulting in Kashmir over geomorphic (10⁴ year) time scales; and (3) Creating a standardized database of fault offsets to help test time-dependent and time-independent seismic hazard models for the Uniform California Rupture Forecast. The Himalayan thrust front in Pakistan is defined by the Salt Range thrust (SRT), the up-dip extension of the plate boundary décollement, the Main Himalayan thrust (MHT). We constrain the convergence rate across the SRT by determining the slip rate for the Kalabagh fault (KF), a tear fault that is linked with the SRT at depth. Based on the age and offset of two alluvial fan apexes from their source canyons, we estimate a slip rate of between 9 and 27 mm/yr (~12-17 mm/yr best estimate) for the KF-SRT fault system. This rate matches well with the geodetically-constrained creep rate for the MHT at depth, suggesting the entire slip budget for the Pakistan Himalaya is accommodated at the thrust front. Because the SRT is cored by salt, the earthquake potential for the fault is inferred to be low, although evidence for seismogenic Holocene rupture on the Kalabagh fault, which is also locally lined with salt, suggests that the frontal fault ruptures in plate boundary earthquakes on the MHT. The primary implications of these findings are that convergence in the Pakistan Himalaya is focused at the thrust front rather than distributed between different faults across the plate boundary. In the Kashmir Himalaya, multiple active faults along the plate boundary suggest that Indo-Eurasian convergence is partitioned between the thrust front and faults to the north. To test how much deformation occurs within the overriding plate, we characterized deformation for the Balapora fault, a high-angle reverse fault on the southwest side of the Kashmir Valley. Based on dated offset stream terraces and alluvial fans, the slip rate for the Balapora fault is consistently between 0.3 and 0.5 mm/yr over time scales varying by an order magnitude between about 40 ka and 400 ka. These slip rates translate to shortening rates of 0.1 mm/yr, or less than 1% of the convergence rate across the Kashmir Himalaya. Earthquake recurrence for the Balapora fault is several thousand years, which is consistent with the low slip rate for the fault. The inference is thus that, the majority of convergence in the Kashmir Himalaya is accommodated near the thrust front, as in the Pakistan Himalaya. For California, a new database was created from thousands of measurements of slip resulting from one or more historical to prehistoric earthquakes for use in seismic hazard models. A new rating scheme characterizes the quality of the offsets. Multiple methods to estimate slip during the last event, average slip and slip-per-event are used to analyze the data. These data provide a first order check for models of earthquake behavior. With the advent of high resolution topographic datasets such as LiDAR, the new methodology serves as a template for inclusion of rapidly-accumulating topographic and paleoseismic data in California as well as to regions such as the Himalayan front, as those types of data are adopted.
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174. [Article] Paleoceanography of the Eastern Equatorial Pacific during the Neogene : synthesis of Leg 138 drilling results
The primary objective of Leg 138 was to provide detailed information about the ocean's response to global climate change during the Neogene. Two north south transects were drilled (95° and 110°W) within ...Citation Citation
- Title:
- Paleoceanography of the Eastern Equatorial Pacific during the Neogene : synthesis of Leg 138 drilling results
- Author:
- Mayer, Larry A., Pisias, Nicklas G., Mix, Alan C.
The primary objective of Leg 138 was to provide detailed information about the ocean's response to global climate change during the Neogene. Two north south transects were drilled (95° and 110°W) within the region of equatorial divergence driven upwelling (and thus high accumulation rates and resolution) and spanning the major equatorial ocean current boundaries (and thus recording a high amplitude signal of the response of the sediment to climatically and/or tectonically driven changes in ocean circulation). The Neogene is marked by a number of well known climatic and tectonic events (the closing of the Isthmus of Panama, the onset of North Atlantic Deep Water (NADW), the rapid uplift of the Himalayas, the major intensification of Northern Hemisphere glaciation), and the response of the ocean before and after these events was a key focus of Leg 138 drilling. To address these objectives at the highest resolution possible, the Leg 138 scientific staff developed a number of new shipboard strategies and analytical procedures. These included the real time analysis of the near continuous gamma ray attenuation porosity evaluator (GRAPE) and susceptibility profiles produced by the multisensor track (MST) on unsplit cores to monitor core recovery and, if necessary, to modify the drilling strategy to ensure proper offset of coring gaps; the collection of near continuous color reflectance data on split cores; the logging of the first hole drilled at each site to optimize drilling and sampling strategies for subsequent holes; and the use of multiple continuous records to unambiguously construct complete composite sections for each site. The complete, continuous records provided by the GRAPE (with a temporal resolution of often yr), in conjunction with an excellent microfossil stratigraphy and often excellent magnetostratigraphy, allowed for astronomical tuning of the stratigraphic record and resulted in a set of internally consistent, high resolution age models that provide a secure, absolute time scale for the past 6 m.y. For the period before 6 m.y., the absolute time calibration is less secure, but it is still better than any previously offered. The high resolution stratigraphic framework of Leg 138 provided new insight into the previously ambiguous tectonic history of the region. By assuming that maximum sedimentation rates along the north south transect would be expected at the equator, the Leg 138 stratigraphy supports the 1985 work of Cox and Engerbretson, which calls for two different poles of rotation of the Pacific Plate during the interval 0-20 Ma. The Leg 138 plate reconstructions also support several previously hypothesized ridge crest jumps and a slowing of the absolute motion of the Nazca Plate at about 5 Ma. Although Leg 138 data that predates about 13 Ma is limited, the impression that one can gain from these data is that the eastern equatorial Pacific was characterized by relatively high carbonate concentrations and accumulation rates before about 11 Ma. This pattern was interrupted occasionally by rapid massive outpourings of near monospecific laminated diatom oozes that probably represent the formation of massive mats along strong surface water fronts. The laminated diatom oozes (LDO) continue to be present in the Leg 138 record (many of them being expressed as seismic reflections) until about 4.4 Ma. Carbonate accumulation rates begin to decline slowly between 11 and 9.8 Ma, when, at about 9.5 Ma, a near complete loss of carbonate (the "carbonate crash") takes place everywhere in the Leg 138 region (and beyond), except at the westernmost sites close to the equator. The "carbonate crash" was a time of fundamental change for the eastern equatorial Pacific, and perhaps for most of the ocean basins. Unlike many of the carbonate variations that precede and postdate it, this "crash" represents a major dissolution event whose effects can be traced seismically in the central and western Pacific. The changes in bottom water chemistry associated with this event (or series of events) appear to be related to the early phases of the closing of the Panama Gateway. The role of NADW initiation and intensification for controlling carbonate accumulation in the eastern equatorial Pacific is still not resolved; however, ocean modeling demonstrates that the closing of the Panama Gateway may also have a direct influence on NADW production. Therefore, the effects of changes in the Panama Gateway sill depth and the production of NADW may be manifested in the history of eastern equatorial Pacific sedimentation. The "carbonate crash" was followed by a recovery of the carbonate system (except in the Guatemala and Peru basins, which never recovered) that led up to the late Miocene/ early Pliocene sedimentation rate maxima, during which equatorial sedimentation rates are as much as five times greater than those of the late Pliocene or Pleistocene. Examination of modern productivity/ preser vation relationships implies that the sedimentation rate maximum was the result of enhanced productivity. The distribution of eolian sediments and isotopic gradients, along with an analysis of the modes of variance in carbonate deposition over the last 6 m.y., suggest a more northerly position of the Intertropical Convergence Zone (ITCZ), a stronger north south gradient across the equator, and a more zonal circulation focused along the equator during the time of maximum sedimentation. The mechanisms suggested for these changes in circulation patterns include the response of the eastern equatorial Pacific to the closing of the Isthmus of Panama, as well as a global increase in the flux of Ca and Si into the oceans, a possible response to evolution of the Himalayas and the Tibetan Plateau. In an effort to understand the response of the climate system to external (orbital) forcing, 6-m.y.-long, continuous records of carbonate (derived from GRAPE), δ¹⁸O and insolation were analyzed and compared. Evolutionary spectral calculations of the variance and coherence among these records indicate that the insolation record is dominated by precessional frequencies, but that the relative importance of the two precessional frequencies has changed significantly over the last 6 m.y. In general, precessional forcing is not found in the carbonate or isotopic records. In the tilt band, however, a linear response is present between solar forcing and the carbonate and isotope records over some intervals. The carbonate record appears to be tightly coupled to the tilt component of insolation before about 1.9 Ma; however, the isotope record does not begin to show sensitivity to orbital tilt until about 4.5 Ma, the time of significant changes in sedimentation patterns in the eastern equatorial Pacific. Only during the last 500,000 yr do all frequencies respond in a similar manner; we also see a marked increase in the response of the isotopic record to orbital forcing (including 100,000- and 400,000-yr periods).
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Part 1 The concentration of seventeen elements in two species of fungus which cause wheat bunt disease, Tilletia caries (DC.)Tul. (TS) and Tilletia controversa Kiihn (DS), were determined by instrumental ...
Citation Citation
- Title:
- Chemical element profiles by instrumental neutron activation analysis : in, part 1, two species of wheat bunt spores, Tilletia caries (DC) Tul. and Tilletia controversa Kühn; part 2, representative sediment and basalt samples taken from a DSDP 678 m core, site 525A, Leg 74, Walvis Ridge
- Author:
- Liu, Yun-gang
Part 1 The concentration of seventeen elements in two species of fungus which cause wheat bunt disease, Tilletia caries (DC.)Tul. (TS) and Tilletia controversa Kiihn (DS), were determined by instrumental neutron activation analysis in 37 TS spore samples, and 31 DS spore samples. Aluminum was chosen as a soil contamination indicator to correct for soil contamination. The plot of the concentrations of the ith element [X[subscript i]] versus Al, yielded the biological concentrations of [X.[subscript i]]. The results show that the biological concentrations of Sc, V, La, and Sm are insignificantly small and that their contents in the spores are essentially all derived from soil dust contamination. For Na and Fe, considerable fractions, 0.15 and 0.60, respectively, of their total concentrations are derived from soil contamination. For other elements, the soil contamination contributions are relatively small compared to their biological concentrations. The "student" t-test was used for comparisons of the geometric means of the element concentrations between the TS and DS spore series. The differences between the mean values of Cl, K, Ca, Mn, Zn, and Br for the TS and CS series are not totally due to random errors within the 95% confidence level. The differences for K and Cl between the TS and DS series are large and outside the ±10- limits; therefore, the concentrations of these two elements can be used as reliable criteria for distinguishing these two species. Also, Br may be useful as a diagnostic trace element due to the significant difference between the Br geometric means of the TS and DS spores. Part 2 Forty sediment and four basement basalt samples, taken from a 678 m core drilled by the DSDP (Deep Sea Drilling Project) at Site 525A, Leg 74 (June 10-15, 1980), as well as sixteen selected basalt samples around the south Atlantic Ocean were subjected to instrumental neutron activation analysis. Thirty-two major, minor, and trace elements were determined. The core from the Wavlis Ridge site (2467 m) consisted of 574.6 m of sediment and 103.5 m of basalt. The downcore element concentration profiles and regression analyses show that the rare earth elements (REE) are present in significant amounts in both the carbonate and non-carbonate phases in sediments; Sr is concentrated in the carbonate phase; most of the other elements determined exist mainly in the non-carbonate (mostly clay) phase. The calculated partition coefficients of the REEs between the carbonate phase and the free REE ion concentrations in sea water were high and increased with decreasing REE ionic radii or increasing atomic number from 3.9x10⁶ for La to 15x10⁶ for Lu. Using the partition coefficients of the REEs in the carbonate and non-carbonate (clay) phases, the REE concentrations in Atlantic sea water were calculated, and the results indicate that the lanthanide concentrations have not been changed significantly in south Atlantic sea water over the past 70 m.y.. The Ce anomaly observed in >95% carbonate sediments is related to the Ce⁺³ concentration in sea water; therefore, the Ce anomaly is a redox (reducing-oxidizing) indicator of sea water. (Essentially, >99.99% of soluble Ce in sea water is present as Ce⁺³.) The REE patterns show no Ce depletion in mollusc shell segments from the late Campanian, and a slight Ce depletion in carbonate phases from the late Paleocene sediments. From early Eocene on, the REE patterns in the carbonate phase show a marked Ce depletion, the same as is observed in carbonates from the late Pleistocene to early Holocene (about 0.3 m.y. ago). The abrupt and striking change in the Ce depletion indicates that sea water was anoxic over the Walvis Ridge during the late Campanian. As the gap between northeast South America (northeast Brazil) and west central Africa (near the southwest corner of the upper half of Africa, e.g., near Liberia) widened and the Walvis Ridge subsided between the late Campanian and late Paleocene, sea water flow between the north Atlantic and south Atlantic oceans increased steadily, and gradually flushed out the anoxic water layer over the Walvis Ridge, thereby achieving oxidation conditions at about 54 m.y. ago, that are similar to present day sea water redox conditions: in the world oceans. The chemical compositions of the basement rocks of the core corresponds to alkalic basalts, not MA-Crean Ridge basalts (MORBs). Only a few basement rocks had been recovered from other Walvis Ridge sites. The results add more evidence which supports the hypothesis that the Wavlis Ridge was formed by a series of volcanoes moving over a "hot spot" near the Mid-Atlantic Ridge. These volcanoes migrated eastward as the South American and African continents drifted away. Most of the basalt samples taken from the southeast Brazilian continental margin also are not similar to MORE. From the bulk chemical composition and the REE pattern, one 112 m.y. old basalt has been identified as an early-stage MORB. To date, this is the oldest oceanic tholeiite recovered from the south Atlantic. This direct evidence indicates that the continental split between South America and Africa commenced ≥112 m.y. ago, and is consistent with the suggestion that the rift between the two continents began about 125 m.y. ago.
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176. [Article] Coastal sand dunes of Oregon and Washington
In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature ...Citation Citation
- Title:
- Coastal sand dunes of Oregon and Washington
- Author:
- Cooper, William Skinner, 1884-
In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature is relatively low in summer and rarely reaches the freezing point in winter. Winter precipitation is heavy, and there is almost no snow; there is a pronounced deficiency in precipitation in summer. The summer wind is a very constant afternoon sea breeze from north to northwest; winter winds are variable but include frequent southwest gales. Longshore currents are governed by the seasonal winds, moving southward in summer and northward in winter. The regional vegetation is dense, tall conifer forest. The influence of man has been comparatively slight: in prehistoric times the starting of forest fires; in historic time moderate disturbance due to grazing and recent efforts to control the movement of the sand. Part II deals with forms and processes. The simplest combination of elements comprises sand, wind, and water. Interaction of these produces two patterns. In the transverse-ridge pattern the individual unit is a ridge essentially normal to the summer wind and moving with it; it is asymmetric in profile with gentle windward slope and steep leeward slope (slipface). Origin and maintenance of this profile are explained in accordance with principles developed in the field of aerodynamics, and conclusions arrived at deductively are confirmed by slow-motion photography of smoke streams on the dunes. The oblique-ridge pattern occurs only where there is full exposure to both seasonal winds, plenty of space, and plenty of sand. These conditions are met only in Region III (Coos Bay dune sheet). The units are much more massive than the transverse ridges and are essentially stationary. Their trend lies between the means of summer and winter winds. A theoretical explanation of their origin and maintenance is presented, and the oblique ridges and the "longitudinal dunes" of certain desert regions are compared. Neither transverse nor oblique ridge is found in stabilized condition. The factor vegetation added to the other three-sand, wind, and water-promotes stabilization. On a prograding shore, successive beach ridges are quickly captured and fixed, and retain their initial form indefinitely. On a retrograding shore the processes are exceedingly complex and involve repeated stabilization and rejuvenation. Two cases are presented: flat shore, with and without abundant sand supply; stabilized dune masses undergoing erosion. In the latter case, the commoner, development involves the following phases: trough blowout, merging of troughs, reduction to deflation base, and precipitation ridge, which may in time become completely stabilized while still retaining its characteristic form. In places sheltered from one or the other of the seasonal winds, usually the summer wind, giant parabola dunes, which may likewise become fixed by vegetation, develop. Part III is a description of the dune localities of the Oregon-Washington coast and an account of their history. Forty per cent of this coast bears dunes of greater or lesser magnitude. Thirty dune localities are grouped in four regions. Region I includes four localities north of Tillamook Head, Oregon, making a continuous strip 53 km long, that bears the parallel beach-dune-ridge pattern associated with progradation. The forms in Regions II, III, and IV, heterogeneous and complex, are those characteristic of retrograding shores. The two principal stabilized forms are the precipitation ridge and the parabola dune. In Regions II, III, and IV the existing features came into being mainly during the last grand period of sea-level rise, and the seaward portions of massive parabola complexes have been sliced away in varying degree by the advancing sea. The beach-ridge dunes of Region I were formed during the period of comparatively stable sea level, with a probable small net lowering, which followed the maximum of sea advance and has extended to the present. Progradation here during this period, in contrast with almost none south of Tillamook Head, has been possible because of the ample bed load carried to the coast by the Columbia River. South of Tillamook Head there is, in a number of well-distributed localities, evidence of three episodes of advance. The first is represented by the strip of thoroughly stabilized dunes that nearly everywhere forms the inner marginal part of the dune complexes. This episode reached its culmination before the sea had attained its maximum of advance-attested by the slicing away of portions of completely stabilized masses. The second advance for the most part fell short of the first, though in a few places it overpassed the limits of the latter; present condition ranges from complete stabilization to vigorous activity. The third episode is represented by active dunes with open access to the shore. In certain localities there are only an inner strip of stabilized dunes and an outer zone of active dunes. It is assumed that in these the visible effects of the second and third episodes have merged. An earlier cycle of dune development, similar to the modern one in character and extent, is proved by eolian sediments containing altered podzolic soils, which make a minor part of the mantle of unconsolidated materials that lies upon the rock platform of the 30-m terrace. The dunes of which these masses are remnants were formed during the next-to-the-last grand period of submergence. Development of the dunes of Regions II, III, and IV, associated with the grand period of submergence, is assigned to the period of deglaciation that followed the Wisconsin maximum, and mainly to the period of rapid deglaciation that began after the Valders-Mankato advance. The beach-ridge dunes of Region I, on the other hand, have developed in their entirety in the time since sea-level rise was succeeded by stability. By analogy, the earlier cycle of dune development was associated with the waning phase of Illinoian glaciation, and it may be assumed that similar dune cycles were associated with the earlier glaciations of the Pleistocene.