A Neocene Erosion Surface in Central Oregon

A landscape, in the old age stage, termed the Ochoco Erosion Surface, bevels the Columbia lavas and Mascall formation of middle Miocene age at a large angle, and the Rattlesnake lower or middle Pliocene at a small angle, in parts of the Ochoco Range and the John Day country of central Oregon. North of the John Day country the Condon Erosion Surface, locally at least a peneplane, probably but at present not demonstrably the correlative of the Ochoco, truncates the Columbia lavas and perhaps The Dalles formation. A pause in the eventful diastrophic history of this part of the Northwest is apparently indicated by these features. Subsequently, during the present or Dayville cycle, the great gorges and valleys have been excavated

A Neocene Erosion Surface in Central Oregon

A landscape, in the old age stage, termed the Ochoco Erosion Surface, bevels the Columbia lavas and Mascall formation of middle Miocene age at a large angle, and the Rattlesnake lower or middle Pliocene at a small angle, in parts of the Ochoco Range and the John Day country of central Oregon. North of the John Day country the Condon Erosion Surface, locally at least a peneplane, probably but at present not demonstrably the correlative of the Ochoco, truncates the Columbia lavas and perhaps The Dalles formation. A pause in the eventful diastrophic history of this part of the Northwest is apparently indicated by these features. Subsequently, during the present or Dayville cycle, the great gorges and valleys have been excavated

Pleistocene And Recent Topographic Changes In The Pacific Coast States

In comparison with the eastern half of North America, great topographic changes have occurred, in the Pacific Coast States during the last three periods of geological time—the Pliocene, Pleistocene, and Recent. During these later periods of geological history the eastern mountains and plains have apparently suffered only relatively gentle upbowing or downwarping, but since the beginning of the Pliocene the western mountains and plateaus have not merely been uplifted thousands of feet but have been strongly folded and broken by faults. In the West, neighboring areas have moved in opposite directions. Some have gone up great distances and now form the high ranges; others have sunk and now either form the valleys into which the erosional detritus from the ranges is being in part deposited or they form estuaries or sounds if, lying near the Coast, they sank below sea-level

The Dalles and Hood River Formations, and the Columbia River Gorge

A definite assignment of geologic dates to the main events of the Cenozoic history of the Columbia Gorge and Columbia plateau-vulcanism, sedimentation, folding, erosion-is manifestly possible only if we know the age of at least some of the formations. Because of their stratigraphic position, the ages of The Dalles beds and of the gravels heretofore known as Satsop lying between the Columbia River lavas and the volcanic Cascades formation in the Gorge have critical value for historical purposes. Some doubt has arisen in recent years regarding the extreme youth heretofore assigned to these sedimentary formations and the consequent recency of the physiographic development of the Columbia River Gorge. The writers and Mr. John H. Maxson devoted about ten days in July 1927 to a study of the region extending from somewhat east of The Dalles to west of Hood River. Efforts were concentrated on securing fossil material from the formations lying on the Columbia lavas and on determining the relations of these formations to each other. A very brief preliminary statement of results has been published. The investigation was made under the general direction of Dr. John C. Merriam, President of the Carnegie Institution of Washington, as part of a broad program of Tertiary history' studies in the Northwest

Age of the "Satsop" and the Dalles Formations of Oregon and Washington

Geologists have differed regarding the ages of the "Satsop" and the Dalles formations of the Columbia River Gorge region. Because of their bearing on the history of the Gorge and for other reasons their ages are important. During a brief investigation of these beds under the auspices of the Carnegie Institution of Washington, the writers secured fragmentary mammalian fossil remains from the Dalles formation representing not a Quaternary, but approximately an upper Miocene or lower Pliocene stage. This age determination is corroborated by the lithologic resemblance of the Dalles beds to the middle Neocene Ellensburg formation of central Washington, by the apparently similar relations of these two formations to the Columbia lavas, and by the induration of the Dalles beds, which is equal to that of lower or middle Neocene deposits of the west, but much greater than that of Quaternary formations

The Dalles and Hood River Formations, and the Columbia River Gorge

A definite assignment of geologic dates to the main events of the Cenozoic history of the Columbia Gorge and Columbia plateau-vulcanism, sedimentation, folding, erosion-is manifestly possible only if we know the age of at least some of the formations. Because of their stratigraphic position, the ages of The Dalles beds and of the gravels heretofore known as Satsop lying between the Columbia River lavas and the volcanic Cascades formation in the Gorge have critical value for historical purposes. Some doubt has arisen in recent years regarding the extreme youth heretofore assigned to these sedimentary formations and the consequent recency of the physiographic development of the Columbia River Gorge. The writers and Mr. John H. Maxson devoted about ten days in July 1927 to a study of the region extending from somewhat east of The Dalles to west of Hood River. Efforts were concentrated on securing fossil material from the formations lying on the Columbia lavas and on determining the relations of these formations to each other. A very brief preliminary statement of results has been published. The investigation was made under the general direction of Dr. John C. Merriam, President of the Carnegie Institution of Washington, as part of a broad program of Tertiary history' studies in the Northwest

Experiments testing seismographic methods for determining crustal structure

This paper sets forth the results of experiments executed with a view to ascertaining the effectiveness of seismographic methods in the determination of the structure of both the more superficial and the deeper parts of the earth's crust

Nature of the late movements on the Haywards rift, central California

San Francisco Bay, with the cities of Berkeley and Oakland on its eastern shore, lies on a depressed block which is demarked rather sharply from a higher-lying dissected area to the northeast. In his masterful discussion of the geology of the region published in the San Francisco Folio 2 Professor Lawson applied the same San Francisco-Marin Block to the lower area. The mountainous area to the northeast was designated the Berkeley Hills Block. The latter presents a rather steep and regular front toward the southwest for seventy miles or more, from San Pablo Bay on the north to beyond Mount Hamilton on the south. The boundary zone between the depressed and the elevated blocks has usually been termed the Haywards fault zone. Professor Lawson indicated that this zone is characterized by both faulting and warping. It is not the purpose of this paper to question generalizations previously published regarding movements along the Haywards fault zone, with which the writer agrees in the main, but to emphasize certain new evidence and to point out its logical interpretation

Geological Conditions Affecting Dams in San Gabriel Canyon

In view of the different plans being considered for the building of high dams in San Gabriel Canyon a statement of the geological conditions as they affect impounding structures in that drainageway may be pertinent and of interest. The writer's examination of the canyon reveals that the geological conditions from its mouth to the forks are quite similar, differing only in minor details. The dominant rocks are gneiss and a variety of coarse-grained intrusive igneous rocks of the general nature of granites and diorites. Dikes of both acid and basic rocks are common. Quartz and calcite veins occur occasionally