Download Roadside Geology of Oregon (Roadside Geology Series) by David D. Alt, Donald W. Hyndman PDF
By David D. Alt, Donald W. Hyndman
As with every of my scans, the intro and desk of contents are on the very finish of the PDF, in order that web page numbers within the TOC are accurate.
Until approximately 2 hundred million years in the past, the western margin of North the United States lay to the east, alongside the current Idaho border, and a wide coastal simple unfold westward into Oregon. the remainder of the country used to be ocean flooring. Then the continent started relocating slowly westward clear of Europe and the ground of the Pacific Ocean started sliding underneath the western facet. that's what created Oregon, and this e-book tells the way it occurred.
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Extra info for Roadside Geology of Oregon (Roadside Geology Series)
Sample text
Like so many old mining camps, the ghost town of Cornucopia is near the contact between a mass of granite and the older rocks that surround it. Nothing remains now of Copperfield and Homestead but old mine dumps and names lightly printed on road maps. Prospectors found ore-bearing quartz veins cutting through old sedimentary rocks in the hills west of the Snake River in the 1890's and mining began in 1910 after a long period of development work. During the first World War the mines and mill went full blast and these were flourishing little places tucked away in the mouth of Hell's Canyon where hardly anyone outside might notice them.
All the rocks in the mountains west ofthe road are metamorphosed sediments and volcanics intruded by granites, all of them at least 150 million years old. Rocks in the hills east ofthe highway are dark volcanics, andesite and basalt, erupted when the western Cascade volcanic chain was active. w sandstone serpentinite greenstone and shale Section across the line of Interstate 5 near Medford. Just what happens at the eastern edge ofthe Klamaths is a difficult question. Do the Klamaths continue northeastward buried beneath younger volcanic rocks of the Cascades and central Oregon to reap- gat pear in the geologically similar Blue Mountains or does some kind of gap filled by other rocks separate these two ranges?
Roadcuts beside the highway are in old sedimentary rocks first laid down on the continental shelf and slope between 300 and 200 million years ago and then shoved together into a crumpled mass when the sinking seafloor scraped them off against the edge of the continent. Some of the hills also contain gabbro, a black igneous rock which must have been part of the oceanic crust itself and some how managed to get scrambled into the mountains instead of sliding back into the earth's interior. And there are intrusions of granitic rock that penetrated the whole mess as molten magma.