Bertha, the tunnel-boring machine.
A mysterious object is blocking an $80-million tunnel boring machine 60-feet underneath a major American city and nobody has any idea what it is. The Blaze
Is it a boulder or a buried railroad car? Oregon Live
12 Dec 2013
What’s Down There?
Mysteries, Seattle
GoneWithTheWind
The West coast has three good possibilities. 1. A granite Dome. Probably not likely as they are really big formations. 2. A mountain top. Seriously there are mountain tops at sea level as a result of the dramatic earth movements over time. Right here in Portland is a mountain top sticking out of the Willamette river maybe 20 feet above the surface. 3. Volcanic rock. Some of this rock is incredibly hard. This seems most likely to me given the volcanic history of the region where they are digging.
SDD
I’m going with #5 — the American League West gutter.
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