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Full-Text Articles in Geology

Day 3. Wednesday, August 13, 2003: Oil Shale, University Of Colorado Boulder. Natural Resources Law Center Aug 2003

Day 3. Wednesday, August 13, 2003: Oil Shale, University Of Colorado Boulder. Natural Resources Law Center

Energy Field Tour 2003 (August 11-16)

8 pages.

Contains references.


Simulation Of Groundwater Flow In Cache Valley, Utah And Idaho, Barry Myers May 2003

Simulation Of Groundwater Flow In Cache Valley, Utah And Idaho, Barry Myers

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A groundwater model of Cache Valley was created using MODFLOW. Steady-state calibration of the model demonstrated that recharge to the lower confined aquifer may occur along the margin of the valley that borders the Wellsville Mountains and the Bear River Range. Steady-state calibration also showed that discharge from the unconfined aquifer may occur along the eastern and western margins of the valley in both the Utah and the Idaho portions of the valley.

Two simulations were run with increased pumping of 3 5 cubic feet per second (1 cubic meter per second) from the principal aquifer. The first simulation was …


From The Rim To The River: The Geomorphology Of Debris Flows In The Green River Canyons Of Dinosaur National Monument, Colorado And Utah, Isaac J. Larsen May 2003

From The Rim To The River: The Geomorphology Of Debris Flows In The Green River Canyons Of Dinosaur National Monument, Colorado And Utah, Isaac J. Larsen

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The Green River canyons of the eastern Uinta Mountains have experienced a 5-year period of high debris flow activity. Catchment factors were studied in watersheds and on debris fans with recent debris flows, leading to the development of a conceptual framework of the hillslope and debris flow processes that deliver sediment to the Green River. Two recent fan deposits were monitored to determine the magnitude and processes of reworking that occur during mainstem floods of varying magnitude.

The dominant debris flow initiation mechanism, termed the firehose effect, occurs when overland flow generated on bedrock slopes cascades down steep cliffs and …


Controls On Channel Organization And Morphology In A Glaciated Basin In The Uinta Mountains, Utah, Betty E. Paepke May 2001

Controls On Channel Organization And Morphology In A Glaciated Basin In The Uinta Mountains, Utah, Betty E. Paepke

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The organization and morphology of Middle Fork Sheep Creek and South Fork Sheep Creek, two mountain streams in the upper Sheep Creek basin, are controlled by the spatial distribution of glacial moraines. Both channels are organized into a reoccurring sequence of steep-gradient reaches changing downstream to low-gradient reaches. Steep-gradient reaches are located where the channels flow through moraine s. Low-gradient reaches are located in meadows downstream of the steep-gradient reaches and immediately upstream of the next moraine. Knickpoints in the longitudinal profiles of both streams coincide with the location of moraines.

Large boulder s, beyond the size transportable by the …


Type Locality For The Great Blue Limestone In The Bingham Nappe, Oquirrh Mountains, Utah, United States Geological Survey Jan 2000

Type Locality For The Great Blue Limestone In The Bingham Nappe, Oquirrh Mountains, Utah, United States Geological Survey

All U.S. Government Documents (Utah Regional Depository)

The Great Blue Limestone was named originally by Spurr (1895) from exposures near the Mercur mining district in the Oquirrh Mountains, Utah. The formation was described in greater detail by Gilluly (1932) in the Ophir mining district. Neither formally established a type locality for this formation in the Oquirrh Mountains. However, the formation has since been correlated broadly with similar sedimentary rocks elsewhere in the adjoining Rocky Mountains and Great Basin regions. For the record, and to assist future correlations, a type measured section of the Great Blue Limestone in the Oquirrh Mountains is located, described, and a detailed measured …


Tertiary Stratigraphy And Structural Geology, Wellsville Mountains To Junction Hills, North-Central Utah, Kathryn M. Goessel May 1999

Tertiary Stratigraphy And Structural Geology, Wellsville Mountains To Junction Hills, North-Central Utah, Kathryn M. Goessel

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

This study integrates detailed mapping of Tertiary deposits along the divide between the lower Bear River basin and the Cache Valley basin with several other techniques to generate a depositional model, define extension-related structures, and compile a geologic history for this part of the northeastern Basin and Range province. The study area is situated along the topographic divide between Box Elder and Cache Counties, Utah, from the Wellsville Mountains north almost to Clarkston Mountain. These ranges are cored by folded and thrusted Paleozoic rocks. They are bound on the west by normal faults of the Wasatch fault zone and on …


Geology Of The Oquirrh Mountains, Utah, United States Geological Survey Jan 1999

Geology Of The Oquirrh Mountains, Utah, United States Geological Survey

All U.S. Government Documents (Utah Regional Depository)

The Oquirrh Mountains are located in north-central Utah, immediately south of the Great Salt Lake, in the easternmost part of the Basin and Range physiographic province. The range consists of northerly-trending aligned peaks 56 kilometers long flanked on the west by Tooele and Rush Valleys and on the east by Jordan and Cedar Valleys. The range hosts several of the more prominent base- and precious-metal and desseminated-gold mining areas in the western United States. The 130-year old Bingham porphyry copper mining district, which is of world-class magnitude in the central part of the range, is still active. The Mercur mining …


A Case For Site Acclimation In The Reintroduction Of The Endangered Razorback Sucker (Xyrauchen Texanus), United States Geological Survey Jan 1999

A Case For Site Acclimation In The Reintroduction Of The Endangered Razorback Sucker (Xyrauchen Texanus), United States Geological Survey

All U.S. Government Documents (Utah Regional Depository)

Two site-acclimation studies (Mueller and Marsh 1998, Foster and Mueller 1999) were conducted in 1997 and 1998. The primary emphasis was habitat use and dispersal but we also examined if the rapid dispersal, typically associated with hatchery-produced razorback suckers (suckers), could be mitigated by allowing fish a period of time to recover from stocking-induced stress. Findings of those studies and existing physiological literature suggest that current stocking protocols may subject stocked fish to unnecessary behavioral or physiological stress that could impact performance and ultimately survival. This report presents those findings and recommends an evaluation of existing stocking procedures for the …


Selected Hydrologic Data For The Central Virgin River Basin Area, Washington And Iron Counties, Utah 1915-97, United States Geological Survey Jan 1998

Selected Hydrologic Data For The Central Virgin River Basin Area, Washington And Iron Counties, Utah 1915-97, United States Geological Survey

All U.S. Government Documents (Utah Regional Depository)

Hydrologic data were collected in Washington and Iron Counties, Utah, from 1995 to 1997 to better understand the hydrologic system. Data from earlier years also are presented. Data collected from wells include well-completion data, water-level measurements, and physical properties of the water. Data collected from springs and surface-water sites include discharge and physical properties of the water. Selected water samples collected from ground- and surface-water sites were analyzed for isotopes, chlorofluorocarbons and dissolved gases.


A Hydrogeochemical Study Of The Evolution Of The Headwaters Of The Bear River In The Uinta Mountains, Utah, Michael F. Leschin May 1997

A Hydrogeochemical Study Of The Evolution Of The Headwaters Of The Bear River In The Uinta Mountains, Utah, Michael F. Leschin

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The headwaters of the Bear River in the Uinta Mountains of Utah provide a good setting in which to examine the influence of geological materials on stream chemistry. Ionic contributions to the stream-water from soils, vegetation, and the atmosphere generally are sparse enough that they do not mask the geologic contributions. Samples from 37 sites on the four major headwater streams and several minor tributaries were examined geochemically. Data derived from the samples allowed the construction of a hydrogeochemical weathering model specific to the study area. A significant feature of this model is that carbonic acid is the dominant chemical …


Hydrochemical Definition Of Ground Water And Surface Water, With An Emphasis On The Origin Of The Ground-Water Salinity In Southern Juab Valley, Juab County, Utah, Heidi K. Hadley May 1996

Hydrochemical Definition Of Ground Water And Surface Water, With An Emphasis On The Origin Of The Ground-Water Salinity In Southern Juab Valley, Juab County, Utah, Heidi K. Hadley

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

As part of a U.S. Geological Survey study in Juab Valley in central Utah from 1991 to 1994, the chemistry of ground - and surface -water samples was determined. Total dissolved solids in the ground water of southern Juab Valley have historically been higher, in general, than ground water in other areas of Utah. Total dissolved solids for ground-water samples from this study ranged from 623 to 3,980 milligrams/liter. High-sulfate chemical data of previous studies suggested that the major source of ground-water salinity is the dissolution of gypsum (hydrous calcium sulfate ) from the Arapien Shale. Sulfur-34 to sulfur-32 isotopic …


Geologic Map Of The Logan Quadrangle, Cache County, Utah, James P. Evans, James P. Mccalpin, David C. Holmes Jan 1996

Geologic Map Of The Logan Quadrangle, Cache County, Utah, James P. Evans, James P. Mccalpin, David C. Holmes

Geosciences Faculty Publications

No abstract provided.


Mafic Volcanism In The Colorado Plateau: Basin And Range Transition Zone, Hurricane, Utah, Alexander Sanchez Dec 1995

Mafic Volcanism In The Colorado Plateau: Basin And Range Transition Zone, Hurricane, Utah, Alexander Sanchez

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Hurricane volcanic field (HVF) is a small-volume (0.48 km3) mafic volcanic field in the Colorado Plateau/Basin & Range Transition Zone located in the eastern part of the St. George basin in southwestern Utah. Strombolian-Hawaiian style eruptions produced thin (10 m) a'a lava flows and cinder (scoria) cones composed of vesicular basalt, bombs and agglutinate. Radiometric dating and geologic relationships demonstrate that the HVF formed over a period of at least 100,000 years. In the upper crust, magma probably rose along joints in sedimentary rocks because chains of volcanic vents follow joint orientation maxima in sedimentary rocks.

Three …


Hydrocarbons And Mineral Resources Of The Uinta Basin, Utah And Colorado, United States Department Of The Interior, Indian Affairs Bureau Jan 1995

Hydrocarbons And Mineral Resources Of The Uinta Basin, Utah And Colorado, United States Department Of The Interior, Indian Affairs Bureau

Mines and Mineral Resources

The Uinta Basin holds special fascination for economic geologists because of its rich and diverse assemblage of mineral and hydrocarbon resources. Due to their presence in rocks of the basin, much effort has been put into assessing and exploiting uranium, phosphate, gold, copper, coal, and evaporite minerals. However, the basin is probably best noted for its extensive and very rich accumulations of hydrocarbons such as, oil, gas, bituminous sandstones, oil shale (shale oil), and gilsonite and other solid and semi-solid hydrocarbon species. More importantly, several of these commodities have proven to be a major source of wealth and resources for …


Hydrogeology And Hydrochemistry Of The East-Central Portion Of The Salt Lake Valley, Utah, As Applied To Wellhead Protection In A Confined To Semiconfined Aquifer, Jeff W. Gadt May 1994

Hydrogeology And Hydrochemistry Of The East-Central Portion Of The Salt Lake Valley, Utah, As Applied To Wellhead Protection In A Confined To Semiconfined Aquifer, Jeff W. Gadt

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The Safe Drinking Water Act includes provisions for state wellhead protection programs which address wellhead protection areas. In Utah, these areas are called drinking water source protection (DWSP) zones. Zones Two and Three are delineated according to analytical or numerical techniques, which are based on hydrogeological and time-of-travel data, as well as recharge information, accumulated through the use of hydrogeologic and hydrochemical techniques. The primary conclusions of this research are:

  1. A fence diagram and site hydrostratigraphic diagram show that the hydrogeology is more complex than previously has been thought. The principal aquifer at the target well site comprises a sequence …


Species Of The Cretaceous Tree Fern Tempskya From Utah, William D. Tidwell, Naomi Hebbert Sep 1992

Species Of The Cretaceous Tree Fern Tempskya From Utah, William D. Tidwell, Naomi Hebbert

Faculty Publications

Nine species of the permineralized stems of Tempskya were investigated from the Lower Cretaceous Cedar Mountain and Burro Canyon Formations, and the lower Upper Cretaceous Dakota Formation in central and southeastern Utah. Tempskya jonesii, T. stichkae, and T. readii are new and are differentiated on the basis of the radial orientation of their dorsiventral stems, their internodal lengths, the lack of sclerenchyma in the inner cortex of T. jonesii, the three nearly continuous zones of sclerenchyma in the inner cortex off T. stichkae, and the completely sclerotic inner cortex of T. readii. Specimens of T. jonesii and T. minor were …


Petrology Of Passive Margin-Epeiric Sea Sediments: The Garden City Formation, North-Central Utah, Susan K. Morgan May 1988

Petrology Of Passive Margin-Epeiric Sea Sediments: The Garden City Formation, North-Central Utah, Susan K. Morgan

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The Lower Ordovician Garden City Formation is part of the thick sequence of Lower Paleozoic limestones, dolostones, and minor siliciclastic sedimentary rocks of the western United States. The carbonate rocks were formed predominantly by shallow water deposition in tropical, passive-margin epeiric seas.

The Garden City Formation is composed of nine lithotypes which represent the various environments. The formation is a storm-influenced transgressive sequence which may be divided into innershelf shallow subtidal and outer-shelf deep subtidal environments separated by a skeletal accumulation. The skeletal accumulation, formed by storm initiation, was a submerged topographic high, below normal wave base. The inner shelf …


Surficial Geology Of The Smithfield Quadrangle, Cache County, Utah, Michael V. Lowe May 1987

Surficial Geology Of The Smithfield Quadrangle, Cache County, Utah, Michael V. Lowe

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The Smithfield 7.5' quadrangle is located about 13.8 kilometers (8.6 miles) south of the Utah-Idaho State Line and occupies the central portion of the eastern side of Cache Valley, Utah. The mapped area contains more than 55 square miles. The Bear River Range on the eastern side of the quadrangle contains stratigraphic units ranging from Precambrian to Quaternary age. Cache Valley contains deposits of Tertiary and Quaternary age. Quaternary units in the Smithfield quadrangle are subdivided into thirty-two map units based on age and genesis. Five ages of Quaternary units are identified, and these units are assigned to one of …


Geology And Mining Industry Of The Tintic District, Utah, George Warren Tower, Jr., George Otis Smith Jan 1987

Geology And Mining Industry Of The Tintic District, Utah, George Warren Tower, Jr., George Otis Smith

All U.S. Government Documents (Utah Regional Depository)

The field work upon which this report is based was begun in July, 1897, and continued without interruption until December of the same year. The area studied is approximated 15 miles square and contains 234 square miles. The topographic maps, which are two in number, were prepared under the direction of Mr. R. U. Goode, Mr. S. S. Gannett doing the triangulation and Messrs. Marshall and Griswold the topography in the fall of 1896 and summer of 1897. The mapping is done on two scales; the larger area, approximately 15 miles square, is mapped on a scale of 1:62,500. This …


Structural Geology Of The Central Part Of Clarkston Mountain, Malad Range, Utah, Douglas A. Green May 1986

Structural Geology Of The Central Part Of Clarkston Mountain, Malad Range, Utah, Douglas A. Green

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The central part of Clarkston Mountain is located in northcentral Utah in the southern part of the Malad Range. It is northwest of Clarkston, Utah. The mapped area measures 2.5 mi. in the north-south direction and 6.5 mi. in the east-west direction. It is within the Basin and Range Province.

The Ute Formation of Middle Cambrian age is the oldest exposed stratigraphic unit. Other Cambrian units, in ascending order, are: Blacksmith Formation, Bloomington Formation, Nounan Formation, and St. Charles Formation. These units consist predominantly of limestone, dolostone, and shale. Units of Ordovician age include the Garden City Formation and the …


Potential Geologic Hazards Near The Thistle Landslide, Utah County, Utah, United States Geological Survey Jan 1986

Potential Geologic Hazards Near The Thistle Landslide, Utah County, Utah, United States Geological Survey

All U.S. Government Documents (Utah Regional Depository)

In mid-April, 1983, an old landslide near Thistle, Utah, began to move, and within days had blocked Spanish Fork Canyon. As the slide's movement continued, construction crews gradually converted the toe of the slide into an earth-filled dam--Thistle dam--that impounded northwest-flowing Spanish Fork River. The resultant reservoir, known as Thistle Lake, was subsequently drained because of uncertainty about the stability of the dam. Recently, officials of Utah County have explored various alternatives for a water-retention structure in the area, including utilization of Thistle dam. The Thistle Slide Committee, established by the State of Utah to evaluate the suitability of using …


Chemical Quality Of Ground Water In Salt Lake Valley, Utah, 1969-85, United States Geological Survey Jan 1986

Chemical Quality Of Ground Water In Salt Lake Valley, Utah, 1969-85, United States Geological Survey

All U.S. Government Documents (Utah Regional Depository)

During 1979-84, 35 wells completed in the principal aquifer in the Salt Lake Valley, Utah, that had been sampled during 1962-67 were resampled to determine if water-quality changes had occurred. The dissolved-solids concentration of the water from 13 of the wells has increased by more than 10 percent since 1962-67.


Interconnected Reproductive And Vegetative Remains Of Populus (Salicaceae) From The Middle Eocene Green River Formation, Northeastern Utah, William D. Tidwell, Steven R. Manchester, David L. Dilcher Jan 1986

Interconnected Reproductive And Vegetative Remains Of Populus (Salicaceae) From The Middle Eocene Green River Formation, Northeastern Utah, William D. Tidwell, Steven R. Manchester, David L. Dilcher

Faculty Publications

A new specimen from the Middle Eocene Evacuation Creek Member of the Green River Formation in northeastern Utah shows a twig with several leaves of Populus wilmattae Crockrell and a fruiting raceme attache. This specimen establishes for the first time the type of fruits borne by P. wilmattae and provides additional characters with which to assess its taxonomic and evolutionary status. An associated seed shows attached placental hairs like those of extant species of Populus. The Green River fossil differs from extant Populus species in having basically palmate leaf venation and in bearing its fruiting axis on a young twig. …


Sequential Thrusting Beneath The Willard Thrust Fault, Wasatch Mountains, Ogden, Utah, Tad William Schirmer May 1985

Sequential Thrusting Beneath The Willard Thrust Fault, Wasatch Mountains, Ogden, Utah, Tad William Schirmer

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The downstructure of viewing geologic maps, balanced and cross sections, and hanging-wall-sequence diagrams are applied to produce the first comprehensive synthesis of the structure below the willard thrust sheet.

Development of the duplex beneath the Willard thrust may be explained with a "piggyback" thrust model where younger thrust slices form below and fold an older, overlying thrust sheet. Progressive failure of the footwall ramp of the Willard thrust sheet extended the sole thrust eastward and produced a duplex consisting of thrust slices (horses) which adhered to the overriding thrust sheet where it ramped from a lower sole thrust to an …


Petrology And Mineralogy Of Tertiary(?) Volcanic Rocks Of Snowville Area, Utah, And Tertiary-Quaternary(?) Volcanic Rocks Of Table Mountain And Holbrook Areas, Idaho, Yunshuen Wang May 1985

Petrology And Mineralogy Of Tertiary(?) Volcanic Rocks Of Snowville Area, Utah, And Tertiary-Quaternary(?) Volcanic Rocks Of Table Mountain And Holbrook Areas, Idaho, Yunshuen Wang

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Basalt flows occur in the Snowville area of north-central Utah and the Table Mountain and Holbrook areas of south-central Idaho. All basalt flows are aphanitic in groundmass, and contain olivine, plagioclase, augite, and opaque oxides. They can be distinguished by texture. Snowville basalt has predominantly subophitic to intergranular textures. Table Mountain basalt is fine grained, with stumpy groundmass plagioclase and equant ilmenite crystals. Holbrook basalt has pilotaxitic to intergranular textures, with the presence of plagioclase phenocrysts and characteristic exsolution lamellae in Fe-Ti oxides. The olivine grains in Holbrook area are intensely oxidized to Fe-Ti oxides.

Snowville basalt contains olivine phenocrysts …


Flora Of The Lower Cretaceous Cedar Mountain Formation Of Utah And Colorado; Part Iii, Icacinoxylon Pittiense N. Sp., William D. Tidwell, Gregory F. Thayn, W. L. Stokes Feb 1985

Flora Of The Lower Cretaceous Cedar Mountain Formation Of Utah And Colorado; Part Iii, Icacinoxylon Pittiense N. Sp., William D. Tidwell, Gregory F. Thayn, W. L. Stokes

Faculty Publications

Icacinoxylon pittiense, a new species of angiospermous wood from the Lower Cretaceous Cedar Mountain Formation of Utah is described and compared with similar fossil and modern woods. It is distinguished from other species of Icacinoxylon by its thick-walled fiber-tracheids with their walls making up at least 50% of the total diameter of the cells, conspicuous bordered pits with obliquely crossing extended apertures on both the tangential and radial walls of its fiber-tracheids, scalariform perforation plates with as few as four or greater than 30 bars, transitional opposite to scalariform pitting on its vessel walls, thick-walled ray cells, and distinct sheath …


Preliminary Geologic Map Of The Nephi 30' By 60' Quadrangle, Carbon, Emery, Juab, Sanpete, Utah, And Wasatch Counties, Utah, United States Geological Survey Jan 1985

Preliminary Geologic Map Of The Nephi 30' By 60' Quadrangle, Carbon, Emery, Juab, Sanpete, Utah, And Wasatch Counties, Utah, United States Geological Survey

All U.S. Government Documents (Utah Regional Depository)

The U.S. Geological Survey is engaged in a program of field studies designed to present the geologic framework of the United States on easily read topographic maps. The maps selected as a base for these geologic data are part of the Army Map Service (AMS) series of 1° by 2° quadrangles at a scale of 1:250,000. The Price, Utah AMS 1:250,000 quadrangle is one of these maps (fig.1). For certain areas, however, chiefly those sectors of the country involved in the Geological Survey's coal exploration program, the geologic data are being compiled on newly developed base maps at a scale …


Bedrock Aquifers Of Eastern San Juan County, Utah, United States Geological Survey Jan 1985

Bedrock Aquifers Of Eastern San Juan County, Utah, United States Geological Survey

All U.S. Government Documents (Utah Regional Depository)

This study is one of a series of studies appraising the water-bearing properties of the Navajo Sandstone and associated formations in southern Utah. The study area is about 4,600 square miles, extending from the Utah-Arizona State line northward to the San Juan-Grand County line and westward from the Utah-Colorado State line to the longitude of about 109 degrees 50 minutes.


Evaluation Of Low-Temperature Geothermal Potential In North-Central Box Elder County, Utah, Matthew C. Davis May 1984

Evaluation Of Low-Temperature Geothermal Potential In North-Central Box Elder County, Utah, Matthew C. Davis

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The purpose of this study was to continue the assessment of low-temperature geothermal resources in Utah started by the Utah Geological and Mineral Survey. The area of interest with in this report is north-central Box Elder County, Utah. Exploration techniques used included chemical analyses of water from wells and springs, temperature surveys, and temperature-depth measurements in unused wells within the study area. The highest water temperatures (31, 30, and 29°C) recorded in this research were located in three separate geographic regions, suggesting that no single warm water occurrence dominates the study area.

Total dissolved solid (TDS) concentrations ranged from 294 …


Structure And Petrology Of Tertiary Volcanic Rocks In Parts Of Toms Cabin Spring And Lucin Nw Quadrangles (Box Elder Co.), Utah, Bruce Edward Scarbrough May 1984

Structure And Petrology Of Tertiary Volcanic Rocks In Parts Of Toms Cabin Spring And Lucin Nw Quadrangles (Box Elder Co.), Utah, Bruce Edward Scarbrough

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A series of late Tertiary rhyolitic and dacitic flows, domes, and minor pyroclastic rocks form an elongate volanic mass along the northwestern Utah-northeastern Nevada border. The structure of the flow banding and the linear arrangement of vents indicate that the mass represents a multi-sourced extrusive complex which erupted through many fissure-type conduits. A 39 km2 area at the southern end of the mass was studied in detail in order to gain a better understanding of the eruptive nature and history of these Tertiary volcanic rocks. Age dating reveals that volcanism in the study area was episodic, and covered a …