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• 1. [Article] Preliminary report on the geology of the Molalla quadrangle, Oregon

  The Molalla quadrangle is located in northwestern Oregon along the eastern edge of Willamette Valley about 30 miles south of Portland. The area includes part of the Western Cascade foothills as well as ...

  Citation × Citation Citation Abstract Copy Title: Preliminary report on the geology of the Molalla quadrangle, Oregon Author: Harper, Herbert Ewing The Molalla quadrangle is located in northwestern Oregon along the eastern edge of Willamette Valley about 30 miles south of Portland. The area includes part of the Western Cascade foothills as well as a portion of the Willamette Valley lowland. The rocks in the Cascade foothills are marine and terrestrial sediments interlayered with volcanic flows and pyroclastics which range from Eocene (?) to Pliocene or early Pleistocene in age. The oldest rocks consist of approximately 1500 feet of basaltic and andesitic lavas, present in the southeastern portion of the area, and described here as the Pre-Butte Creek lavas. The base or lower part of the series contains interbedded marine pebble conglomerates presumably of Eocene age. To the southwest the laves are unconformably ever-lain with about 1200 feet of marine and terrestrial sediments which have been termed the Butte Creek beds. Field relations indicate a correlation of these sediments with the Oligocene Illahe sandstone, while the faunal study made by Durham suggests a lower Miocene age. In the southwestern part of the quadrangle the Butte Creek beds are unconformably overlain by the middle Miocene Stayton lavas. Several hundred feet of pyroclastics and terrestrial sediments considered early Pliocene in age and described as the Molalla formation are exposed along Molalla River in the eastern and northeastern part of the quadrangle. They rest unconformably on the Pre-Butte Creek lavas and are overlain by Pliocene or early Pleistocene Boring lavas. Where exposed along the western edge of the Cascade foothills these older formations are covered by middle Pleistocene alluvial deposits which blanket the Willamette valley lowland. All of the Tertiary rocks have been tilted or gently folded. Dips observed in the Butte Creek beds in the southern half of the area average about 6 degrees and indicate an elongate domal fold trending northeasterly. A regional dip of 5 to 8 degrees to the northwest is present in the Molallla formation in the northern part of the area. Minor normal faulting in present locally in the Butte Creek beds. Residual and transported high-alumina clays are present in the Molalla formation. Exploration by the United States Bureau of Mines and Unites States Geological Survey revealed an estimated 53,460,000 wet tons of ore in the Molalla area. Title: Preliminary report on the geology of the Molalla quadrangle, Oregon Author: Harper, Herbert Ewing The Molalla quadrangle is located in northwestern Oregon along the eastern edge of Willamette Valley about 30 miles south of Portland. The area includes part of the Western Cascade foothills as well as a portion of the Willamette Valley lowland. The rocks in the Cascade foothills are marine and terrestrial sediments interlayered with volcanic flows and pyroclastics which range from Eocene (?) to Pliocene or early Pleistocene in age. The oldest rocks consist of approximately 1500 feet of basaltic and andesitic lavas, present in the southeastern portion of the area, and described here as the Pre-Butte Creek lavas. The base or lower part of the series contains interbedded marine pebble conglomerates presumably of Eocene age. To the southwest the laves are unconformably ever-lain with about 1200 feet of marine and terrestrial sediments which have been termed the Butte Creek beds. Field relations indicate a correlation of these sediments with the Oligocene Illahe sandstone, while the faunal study made by Durham suggests a lower Miocene age. In the southwestern part of the quadrangle the Butte Creek beds are unconformably overlain by the middle Miocene Stayton lavas. Several hundred feet of pyroclastics and terrestrial sediments considered early Pliocene in age and described as the Molalla formation are exposed along Molalla River in the eastern and northeastern part of the quadrangle. They rest unconformably on the Pre-Butte Creek lavas and are overlain by Pliocene or early Pleistocene Boring lavas. Where exposed along the western edge of the Cascade foothills these older formations are covered by middle Pleistocene alluvial deposits which blanket the Willamette valley lowland. All of the Tertiary rocks have been tilted or gently folded. Dips observed in the Butte Creek beds in the southern half of the area average about 6 degrees and indicate an elongate domal fold trending northeasterly. A regional dip of 5 to 8 degrees to the northwest is present in the Molallla formation in the northern part of the area. Minor normal faulting in present locally in the Butte Creek beds. Residual and transported high-alumina clays are present in the Molalla formation. Exploration by the United States Bureau of Mines and Unites States Geological Survey revealed an estimated 53,460,000 wet tons of ore in the Molalla area. Close

• 2. [Article] Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho

  The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been ...

  Citation × Citation Citation Abstract Copy Title: Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho Author: Moran, John Lee The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been divided into 23 mapped units. Pre-Belt metamorphic basement rocks are overlain unconformably by 3,433 feet of Paleozoic strata included in eleven formations. These formations represent all of the periods of the Paleozoic except the Ordovician and Silurian. Nine formations represent all the periods of the Mesozoic and total approximately 3,127 feet in thickness. Cenozoic units present in the area are basalts and rhyolites, landslide debris, glacial deposits, and alluvium. The major structure of the thesis area is a fault block that is the result of uplifting and tilting of the east-west trending Centennial Range during the downwarp of the Snake River Plain in late Pliocene and Pleistocene time. No stratigraphic or structural conditions in the thesis area are favorable for the accumulation and entrapment of oil and gas. Phosphorite has been mined from the Phosphoria Formation in the area. Title: Structure and stratigraphy of the Sheep Mountain area, Centennial Range, Montana-Idaho Author: Moran, John Lee The thesis area includes 44 square miles of the Centennial Range in Beaverhead County, Montana, and Clark County, Idaho. The rocks exposed in the area range in age from Precambrian to Recent and have been divided into 23 mapped units. Pre-Belt metamorphic basement rocks are overlain unconformably by 3,433 feet of Paleozoic strata included in eleven formations. These formations represent all of the periods of the Paleozoic except the Ordovician and Silurian. Nine formations represent all the periods of the Mesozoic and total approximately 3,127 feet in thickness. Cenozoic units present in the area are basalts and rhyolites, landslide debris, glacial deposits, and alluvium. The major structure of the thesis area is a fault block that is the result of uplifting and tilting of the east-west trending Centennial Range during the downwarp of the Snake River Plain in late Pliocene and Pleistocene time. No stratigraphic or structural conditions in the thesis area are favorable for the accumulation and entrapment of oil and gas. Phosphorite has been mined from the Phosphoria Formation in the area. Close

• 3. [Article] Geology of the Picture Gorge quadrangle, Oregon

  There are seven stratigraphic units exposed in the Picture Gorge quadrangle, a 204-square mile area in east-central Oregon. isolated exposures of pre-Cretaceous serpentinites, metalimestones, and other ...

  Citation × Citation Citation Abstract Copy Title: Geology of the Picture Gorge quadrangle, Oregon Author: White, Willis Harkness There are seven stratigraphic units exposed in the Picture Gorge quadrangle, a 204-square mile area in east-central Oregon. isolated exposures of pre-Cretaceous serpentinites, metalimestones, and other metamorphic rocks record marine deposition of sands silts, and limy sediments followed by burial, lithification, peridotite intrusion, and several periods of deformation. Intrusion and deformation were accompanied by serpentinization, silcification. and calcite veination. Cretaceous conglomerates and intercalated sandstones, which unconformably overlie the metamorphic rocks, are a result of fluvial deposition in a nearshore or continental environment, burial, lithification, uplift, and erosion. Pebbles were derived from plutonicmetamorphic highlands. The Eocene Clamo Formation unconformably overlies the Cretaceous rocks and is made up of basalt conglomerate, silicified conglomerate, andesite breccias, and andesite flows. The fossiliferous John Day Formation, Oligo-Miocene in age, lies unconformably on the Clamo Formation and is pyroclastic in character. Ash was wind-transported from trachytic-andesitic sources to the west and deposited on land, in lakes, and in swamps. The 2, 400-foot section of volcanic siltstones and waterlaid volcaniclastic rocks includes some basalt near the base and an ash-flow tuff near the middle. The John Day Formation was folded slightly after consolidation. The fissure-fed Middle Mjocene Columbia River Basalt flows, at least 2, 300 feet thick, blanket 124 square miles of the quadrangle. Modal analyses of thin sections from 22 basalt flows suggest that flows cannot be correlated on the basis of mineralogy. Correlation must involve a combination of criteria, such as color, texture, and nature of outcrop, together with mineralogy and chemical analyses. Interfiow breccias, tuffs, volcanic siltstones and sandstones, dikes, and an irregular intrusion are also present. The Columbia River Basalt unconformably overlies the John Day Formation. After emplacement, the basalt flow rocks were folded into the west-trending Sunflower anticline and John Day syncline. Normal faulting occurred on the shared flank of the two folds. The Upper Miocene Mascall Formation lies unconformably upon the Columbia River Basalt. About 400 feet of well-bedded, rhy-. olitic volcanic siltstones and intercalated sand and gravel lenses suggest eoliari and fluvial deposition of ash in lakes and swamps. Folding and faulting occurred along the same trends which were active during Columbia River Basalt time. 'lhe Plio-Pleistocene Rattlesnake Formation rests with pronounced angular unconformity on the Mascall Formation. About 10 feet of poorly consolidated fluvial gravels enclose a 38-foot-thick ash-flow tuff. Pleistocene and recent events include capture of the middle fork of the John Day River, slumping, development of pediments, formation of stone garlands, stone stripes, and talus-free mounds, and deposition of stream gravels. An andesitic, hornblende-bearing white volcanic ash was deposited by wind. Title: Geology of the Picture Gorge quadrangle, Oregon Author: White, Willis Harkness There are seven stratigraphic units exposed in the Picture Gorge quadrangle, a 204-square mile area in east-central Oregon. isolated exposures of pre-Cretaceous serpentinites, metalimestones, and other metamorphic rocks record marine deposition of sands silts, and limy sediments followed by burial, lithification, peridotite intrusion, and several periods of deformation. Intrusion and deformation were accompanied by serpentinization, silcification. and calcite veination. Cretaceous conglomerates and intercalated sandstones, which unconformably overlie the metamorphic rocks, are a result of fluvial deposition in a nearshore or continental environment, burial, lithification, uplift, and erosion. Pebbles were derived from plutonicmetamorphic highlands. The Eocene Clamo Formation unconformably overlies the Cretaceous rocks and is made up of basalt conglomerate, silicified conglomerate, andesite breccias, and andesite flows. The fossiliferous John Day Formation, Oligo-Miocene in age, lies unconformably on the Clamo Formation and is pyroclastic in character. Ash was wind-transported from trachytic-andesitic sources to the west and deposited on land, in lakes, and in swamps. The 2, 400-foot section of volcanic siltstones and waterlaid volcaniclastic rocks includes some basalt near the base and an ash-flow tuff near the middle. The John Day Formation was folded slightly after consolidation. The fissure-fed Middle Mjocene Columbia River Basalt flows, at least 2, 300 feet thick, blanket 124 square miles of the quadrangle. Modal analyses of thin sections from 22 basalt flows suggest that flows cannot be correlated on the basis of mineralogy. Correlation must involve a combination of criteria, such as color, texture, and nature of outcrop, together with mineralogy and chemical analyses. Interfiow breccias, tuffs, volcanic siltstones and sandstones, dikes, and an irregular intrusion are also present. The Columbia River Basalt unconformably overlies the John Day Formation. After emplacement, the basalt flow rocks were folded into the west-trending Sunflower anticline and John Day syncline. Normal faulting occurred on the shared flank of the two folds. The Upper Miocene Mascall Formation lies unconformably upon the Columbia River Basalt. About 400 feet of well-bedded, rhy-. olitic volcanic siltstones and intercalated sand and gravel lenses suggest eoliari and fluvial deposition of ash in lakes and swamps. Folding and faulting occurred along the same trends which were active during Columbia River Basalt time. 'lhe Plio-Pleistocene Rattlesnake Formation rests with pronounced angular unconformity on the Mascall Formation. About 10 feet of poorly consolidated fluvial gravels enclose a 38-foot-thick ash-flow tuff. Pleistocene and recent events include capture of the middle fork of the John Day River, slumping, development of pediments, formation of stone garlands, stone stripes, and talus-free mounds, and deposition of stream gravels. An andesitic, hornblende-bearing white volcanic ash was deposited by wind. Close

• 4. [Article] The structure and stratigraphy of a portion of the Trout Creek Mountains, Harney County, Oregon

  The thesis area is located in the southeastern corner of Harney County, Oregon. This portion of Oregon is situated in the northern part of the Basin and Range province, and is characterized by both mafic ...

  Citation × Citation Citation Abstract Copy Title: The structure and stratigraphy of a portion of the Trout Creek Mountains, Harney County, Oregon Author: Carlton, Richard W. The thesis area is located in the southeastern corner of Harney County, Oregon. This portion of Oregon is situated in the northern part of the Basin and Range province, and is characterized by both mafic and silicic extrusives, and localized nonmarine sediments and tuffs ranging in age from middle (?) Miocene to Recent. The rocks of Miocene and some Pliocene age have been cut by normal faults forming typical Basin and Range structure. The base of the stratigraphic sequence within the thesis area is formed by 775 feet of thin, highly porphyritic basalt flows. On the basis of petrographic and field similarities, these basalts have been correlated with the Steens Basalt of Fuller (1931). Overlying the porphyritic basalts are 980 feet of fine-grained, andesitic basalt flows, and flow breccias. These basalts superficially resemble the Steens Mountain volcanic series of Fuller but they occupy a higher stratigraphic position and may be correlative with the Owyhee Basalt of Renick (1931). Covering the andesitic basalt, but generally poorly exposed are approximately 155 feet of vitric and lithic-vitric air fall tuffs. These tuffs and the overlying ash flow tuffs may be genetically related and probably represent a period of silicic extrusion within the thesis area. Four ash flow tuffs are recognized and described. They appear to have been extruded over a short period of time and may represent a compound cooling unit. The basal ash flow (unit one) is 330 feet thick and characterized by large flattened pumice fragments in the middle welded zone. Covering the basal ash flow is a 230 foot thick ash flow (unit two) composed of a nonwelded base, a dense vitrophyre, and a thick partly welded upper zone. A third ash flow (unit three) whose maximum thickness is 225 feet overlies unit two and is characterized by extremely flattened pumice fragments and platiness. A fourth ash flow (unit four) found only on Red Mountain overlies unit three and has a maximum thickness of 10 feet. The ash flow tuffs are probably not related to the Canyon Rhyolite of Merriam (1910) and are middle (?) to late Miocene in age. Locally overlying the ash flow tuffs is a thick sequence of varicolored, thickly bedded vitric tuffs. These tuffs are correlated with the Trout Creek Formation on the basis of similar stratigraphic position. Stratigraphically above the Trout Creek Formation is a series of coarse angular conglomerates and fine lacustrine sediments which were deposited in stream channels, and as alluvial fans and slope wash during periods of high stream discharge. These sediments are correlated with the Turn-Turn Conglomerates found on the west side of Pueblo Valley. The Turn-Turn Conglomerates are covered on the west by Pliocene and Pleistocene terrace deposits composed primarily of unconsolidated volcanic gravels and pebbles. Structurally the western half of the thesis area is part of the Pueblo Valley graben while the eastern half forms the Trout Creek Mountains. Most of the faults cut the ash flow tuffs and strike within 30° east or west of due north. Donath postulates that this fault pattern may represent original conjugate strike slip shears caused by a north-south maximum principal stress. At a later time block faulting occurred along the previously formed shear zones forming the present topography. Title: The structure and stratigraphy of a portion of the Trout Creek Mountains, Harney County, Oregon Author: Carlton, Richard W. The thesis area is located in the southeastern corner of Harney County, Oregon. This portion of Oregon is situated in the northern part of the Basin and Range province, and is characterized by both mafic and silicic extrusives, and localized nonmarine sediments and tuffs ranging in age from middle (?) Miocene to Recent. The rocks of Miocene and some Pliocene age have been cut by normal faults forming typical Basin and Range structure. The base of the stratigraphic sequence within the thesis area is formed by 775 feet of thin, highly porphyritic basalt flows. On the basis of petrographic and field similarities, these basalts have been correlated with the Steens Basalt of Fuller (1931). Overlying the porphyritic basalts are 980 feet of fine-grained, andesitic basalt flows, and flow breccias. These basalts superficially resemble the Steens Mountain volcanic series of Fuller but they occupy a higher stratigraphic position and may be correlative with the Owyhee Basalt of Renick (1931). Covering the andesitic basalt, but generally poorly exposed are approximately 155 feet of vitric and lithic-vitric air fall tuffs. These tuffs and the overlying ash flow tuffs may be genetically related and probably represent a period of silicic extrusion within the thesis area. Four ash flow tuffs are recognized and described. They appear to have been extruded over a short period of time and may represent a compound cooling unit. The basal ash flow (unit one) is 330 feet thick and characterized by large flattened pumice fragments in the middle welded zone. Covering the basal ash flow is a 230 foot thick ash flow (unit two) composed of a nonwelded base, a dense vitrophyre, and a thick partly welded upper zone. A third ash flow (unit three) whose maximum thickness is 225 feet overlies unit two and is characterized by extremely flattened pumice fragments and platiness. A fourth ash flow (unit four) found only on Red Mountain overlies unit three and has a maximum thickness of 10 feet. The ash flow tuffs are probably not related to the Canyon Rhyolite of Merriam (1910) and are middle (?) to late Miocene in age. Locally overlying the ash flow tuffs is a thick sequence of varicolored, thickly bedded vitric tuffs. These tuffs are correlated with the Trout Creek Formation on the basis of similar stratigraphic position. Stratigraphically above the Trout Creek Formation is a series of coarse angular conglomerates and fine lacustrine sediments which were deposited in stream channels, and as alluvial fans and slope wash during periods of high stream discharge. These sediments are correlated with the Turn-Turn Conglomerates found on the west side of Pueblo Valley. The Turn-Turn Conglomerates are covered on the west by Pliocene and Pleistocene terrace deposits composed primarily of unconsolidated volcanic gravels and pebbles. Structurally the western half of the thesis area is part of the Pueblo Valley graben while the eastern half forms the Trout Creek Mountains. Most of the faults cut the ash flow tuffs and strike within 30° east or west of due north. Donath postulates that this fault pattern may represent original conjugate strike slip shears caused by a north-south maximum principal stress. At a later time block faulting occurred along the previously formed shear zones forming the present topography. Close

• 5. [Article] Geology of part of the northeast quarter of the Mitchell quadrangle, Oregon

  The thesis area covers 165 square miles including the greater part of the northeastern quarter of the Mitchell quadrangle in north-central Oregon. The three stratigraphic units exposed in the area consist ...

  Citation × Citation Citation Abstract Copy Title: Geology of part of the northeast quarter of the Mitchell quadrangle, Oregon Author: Patterson, Robert Lynn The thesis area covers 165 square miles including the greater part of the northeastern quarter of the Mitchell quadrangle in north-central Oregon. The three stratigraphic units exposed in the area consist of a variety of Tertiary volcanic rocks including the Clarno Formation, the John Day Formation, and the Columbia River Basalt. The Clarno Formation of Eocene to Early Oligocene age is the oldest rock unit in the thesis area. From oldest to youngest, the mapped units include volcanic boulder conglomerates, andesite and basalt flows and flow breccias, tuffaceous sandstones intercalated with lava flows, and twelve plugs and dikes of andesite and basalt. The composition, lack of sorting, stratigraphic and structural features, and the included flora indicate that the volcanic boulder conglomerates were deposited as mudflows on a terrain of high relief in a humid, subtropical climate. Andesite lavas were extruded intermittently during deposition of the mudflows resulting in complex intertonguing of the two rock types. Later, Clarno lavas poured from numerous isolated fissures and covered the volcanic boulder conglomerates. Near Middle Oligocene time the formation was folded into a broad NE-trending anticline which swings sharply eastward in the north-central half of the area. Following uplift, the Clarno rocks were eroded into a surface of moderate relief and thick fossil soils developed on scoriaceous portions of the lava flows. The John Day Formation of Late Oligocene to Early Miocene age consists of ash flows and ash falls of acid to intermediate pyroclastic material which were deposited unconformably on the deformed and eroded Clarno rocks. These pyroclastics were erupted from unknown local sources, and probably from distant volcanoes to the west. Much of the material deposited on the pre-Miocene anticlinal crest was reworked by streams and formed thick tuff beds on the flanks of the fold. In Middle Miocene time the consolidated John Day Formation was slightly folded parallel to pre-Miocene anticlinal trends and underwent erosion. The Columbia River Basalt was extruded from fissures onto the tuffs during Middle Miocene time. Following deposition the thick layers of basalt were gently folded as the pre-Miocene anticlinal trend again served as the pattern for mild uplift and deformation in latest Miocene time. Rocks younger than Middle Miocene were either never deposited on the basalt plateaus of the area, or have been completely removed by erosion. In Pleistocene and Recent time the plateaus were dissected and the flows were eroded from the anticlinal crest. Landslide, fluvial, and terrace deposits were laid down in the valleys. White volcanic ash was transported by wind from an unknown source and intercalated with Recent fluvial and slope wash deposits. Title: Geology of part of the northeast quarter of the Mitchell quadrangle, Oregon Author: Patterson, Robert Lynn The thesis area covers 165 square miles including the greater part of the northeastern quarter of the Mitchell quadrangle in north-central Oregon. The three stratigraphic units exposed in the area consist of a variety of Tertiary volcanic rocks including the Clarno Formation, the John Day Formation, and the Columbia River Basalt. The Clarno Formation of Eocene to Early Oligocene age is the oldest rock unit in the thesis area. From oldest to youngest, the mapped units include volcanic boulder conglomerates, andesite and basalt flows and flow breccias, tuffaceous sandstones intercalated with lava flows, and twelve plugs and dikes of andesite and basalt. The composition, lack of sorting, stratigraphic and structural features, and the included flora indicate that the volcanic boulder conglomerates were deposited as mudflows on a terrain of high relief in a humid, subtropical climate. Andesite lavas were extruded intermittently during deposition of the mudflows resulting in complex intertonguing of the two rock types. Later, Clarno lavas poured from numerous isolated fissures and covered the volcanic boulder conglomerates. Near Middle Oligocene time the formation was folded into a broad NE-trending anticline which swings sharply eastward in the north-central half of the area. Following uplift, the Clarno rocks were eroded into a surface of moderate relief and thick fossil soils developed on scoriaceous portions of the lava flows. The John Day Formation of Late Oligocene to Early Miocene age consists of ash flows and ash falls of acid to intermediate pyroclastic material which were deposited unconformably on the deformed and eroded Clarno rocks. These pyroclastics were erupted from unknown local sources, and probably from distant volcanoes to the west. Much of the material deposited on the pre-Miocene anticlinal crest was reworked by streams and formed thick tuff beds on the flanks of the fold. In Middle Miocene time the consolidated John Day Formation was slightly folded parallel to pre-Miocene anticlinal trends and underwent erosion. The Columbia River Basalt was extruded from fissures onto the tuffs during Middle Miocene time. Following deposition the thick layers of basalt were gently folded as the pre-Miocene anticlinal trend again served as the pattern for mild uplift and deformation in latest Miocene time. Rocks younger than Middle Miocene were either never deposited on the basalt plateaus of the area, or have been completely removed by erosion. In Pleistocene and Recent time the plateaus were dissected and the flows were eroded from the anticlinal crest. Landslide, fluvial, and terrace deposits were laid down in the valleys. White volcanic ash was transported by wind from an unknown source and intercalated with Recent fluvial and slope wash deposits. Close

• 6. [Article] Subsurface structural evolution along the northern Whittier fault zone of the eastern Los Angeles basin, Southern California

  The Whittier fault forms the central part of a fault system extending from the East Montebello fault at Whittier Narrows to the Elsinore fault, which is traced as far as the Mexican border. The Whittier ...

  Citation × Citation Citation Abstract Copy Title: Subsurface structural evolution along the northern Whittier fault zone of the eastern Los Angeles basin, Southern California Author: Herzog, David W. The Whittier fault forms the central part of a fault system extending from the East Montebello fault at Whittier Narrows to the Elsinore fault, which is traced as far as the Mexican border. The Whittier fault forms a restraining bend in this fault system, resulting in uplift of the Puente Hills. The northwestern part of the Whittier fault in the Whittier oil field in the eastern Los Angeles basin strikes approximately N65°W and dips 70-75° northeast. The fault is near the range front of the Puente Hills northwest of Turnbull Canyon, and within the Puente Hills to the southeast. The central reach of the Whittier fault had normal separation in the Relizian and Luisian stages of the middle Miocene. From the Mohnian through Repettian stages of the late Miocene and early Pliocene, little, if any, offset occurred until the initiation of reverse offset in the Venturian stage of the late Pliocene. A component of right-lateral strike-slip may have been added near the end of the Pliocene, coinciding with the formation of the Elsinore fault. The Workman Hill and Whittier Heights faults may have formed in the late Pliocene to early Pleistocene, coinciding with the possible initiation of strike-slip on the Whittier fault. The present sense of slip on the Whittier fault southeast of the study area is nearly pure right-lateral strike-slip, with a slip rate of 2-3 mm/yr. The northwestern part of the Whittier fault has a component of reverse slip of approximately 1 mm/yr. The amount of strike-slip on this part of the fault was not determined by this study. The Rideout Heights, 304, and 184 low-amplitude anticlines formed in the Whittier oil field area in the late Miocene and early Pliocene. The Rideout Heights anticline is a southwest-verging fault-propagation fold trending northwesterly from the mouth of Turnbull Canyon through the Rideout Heights area. Strata are overturned in the southwest limb of the fold, and normally dipping in the northeast limb; the fold has been cut along its hinge by the Whittier fault. The 304 and 184 anticlines are north-verging and appear to be beddingplane shear folds in the northeast limb of the La Habra syncline. Recent strike-slip on the Whittier fault may have reactivated the 184 anticline, causing uplift of the footwall block south of Turnbull Canyon. North of Turnbull Canyon, the Whittier fault is at the range front with no evidence of Quaternary footwall uplift. The 304 anticline could be a fault-propagation fold from a previously-unknown southwest dipping blind reverse fault south of the Whittier fault; uplift on this fold could also be the cause of footwall uplift south of Turnbull Canyon. Active fault traces, possibly strike-slip, are on or near the Whittier fault south of Turnbull Canyon, but to the north, recent offsets appear to be northeast of the Whittier fault in the Puente Hills. These offsets may represent an attempt of the Whittier fault to straighten itself by bypassing the restraining bend at Turnbull Canyon. so, this movement is too recent to offset conglomerate beds more than a few tens of meters. Title: Subsurface structural evolution along the northern Whittier fault zone of the eastern Los Angeles basin, Southern California Author: Herzog, David W. The Whittier fault forms the central part of a fault system extending from the East Montebello fault at Whittier Narrows to the Elsinore fault, which is traced as far as the Mexican border. The Whittier fault forms a restraining bend in this fault system, resulting in uplift of the Puente Hills. The northwestern part of the Whittier fault in the Whittier oil field in the eastern Los Angeles basin strikes approximately N65°W and dips 70-75° northeast. The fault is near the range front of the Puente Hills northwest of Turnbull Canyon, and within the Puente Hills to the southeast. The central reach of the Whittier fault had normal separation in the Relizian and Luisian stages of the middle Miocene. From the Mohnian through Repettian stages of the late Miocene and early Pliocene, little, if any, offset occurred until the initiation of reverse offset in the Venturian stage of the late Pliocene. A component of right-lateral strike-slip may have been added near the end of the Pliocene, coinciding with the formation of the Elsinore fault. The Workman Hill and Whittier Heights faults may have formed in the late Pliocene to early Pleistocene, coinciding with the possible initiation of strike-slip on the Whittier fault. The present sense of slip on the Whittier fault southeast of the study area is nearly pure right-lateral strike-slip, with a slip rate of 2-3 mm/yr. The northwestern part of the Whittier fault has a component of reverse slip of approximately 1 mm/yr. The amount of strike-slip on this part of the fault was not determined by this study. The Rideout Heights, 304, and 184 low-amplitude anticlines formed in the Whittier oil field area in the late Miocene and early Pliocene. The Rideout Heights anticline is a southwest-verging fault-propagation fold trending northwesterly from the mouth of Turnbull Canyon through the Rideout Heights area. Strata are overturned in the southwest limb of the fold, and normally dipping in the northeast limb; the fold has been cut along its hinge by the Whittier fault. The 304 and 184 anticlines are north-verging and appear to be beddingplane shear folds in the northeast limb of the La Habra syncline. Recent strike-slip on the Whittier fault may have reactivated the 184 anticline, causing uplift of the footwall block south of Turnbull Canyon. North of Turnbull Canyon, the Whittier fault is at the range front with no evidence of Quaternary footwall uplift. The 304 anticline could be a fault-propagation fold from a previously-unknown southwest dipping blind reverse fault south of the Whittier fault; uplift on this fold could also be the cause of footwall uplift south of Turnbull Canyon. Active fault traces, possibly strike-slip, are on or near the Whittier fault south of Turnbull Canyon, but to the north, recent offsets appear to be northeast of the Whittier fault in the Puente Hills. These offsets may represent an attempt of the Whittier fault to straighten itself by bypassing the restraining bend at Turnbull Canyon. so, this movement is too recent to offset conglomerate beds more than a few tens of meters. Close