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View Diary: The Daily Bucket--Once there was an ocean, now there is no ocean there (71 comments)

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  •  Thanks Ernest, (2+ / 0-)
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    RiveroftheWest, Polly Syllabic

    especially for the link to the Ore Bin.  Gee, the West Hills I drive through several times a week are old volcanos.  And they ran a deep underground train tunnel right through those too.

    “The answer must be, I think, that beauty and grace are performed whether or not we will or sense them. The least we can do is try to be there.” ― Annie Dillard, Pilgrim at Tinker Creek

    by 6412093 on Sat Aug 31, 2013 at 03:20:26 PM PDT

    [ Parent ]

    •  There are volcanic vents mapped in the West Hills (2+ / 0-)
      Recommended by:
      RiveroftheWest, Polly Syllabic

      but those hills, more properly named the Tualatin Mountains, are more attributable to tectonic movement along faults (Portland Hills Fault, Sylvan Fault). There is a small area of Boring Lava near the west end of the tunnel, but most of the volcanic rock you see in the West Hills is basalt of the Columbia River Basalt Group, which originated in western Idaho, eastern Oregon, and eastern Washington.

      Here is a nice summary of the general geology of the Portland area, from a field guide associated with a Geological Society of America meeting that was held in Portland in 2009.

      from the field guide:

      The 3-mile-long Robertson MAX tunnel through the Tualatin Mountains was constructed between 1993 and 1998. The western third was excavated by drilling and blasting, the eastern portion with a tunnel boring machine. The difference in construction techniques was due to the variable geology encountered along the way. The tunnel boring machine had particular trouble and was plagued with geology-related delays in its first years of operation. Thus it is fitting that the public art in the Washington Park/Zoo station includes a beautifully displayed core (Figure 5-1) from one of the many geotechnical borings made along the tunnel route. This is in fact the most accessible and complete “exposure” of Portland geology in existence, so take a moment to walk along the core as it traverses Columbia River Basalt, Boring Lava, and loess. The station is located 80 m below ground surface, and is the deepest train station in North America. Unfortunately, the entire tunnel is lined with concrete, so there is nothing to see out the light rail car windows! If you have a moment to ride the elevators to the surface, you will note that instead of floors, the display reads in geologic time. Beautiful landscaping with columns of Columbia River Basalt surrounds the surface entrance to the station

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