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I've got a photo of a giant rock for you. This thing is called 'Moss Rock' and I shot this from a half mile away with a long lens. Look at the giant boulder in the middle of the shot - not at the Olympic Mountains, those are for tomorrow!
I want to make sure you understand the scale of this thing. Take a look at the houses in front and on the right.
When Cathy and I first moved here, we moved into an apartment on the other side of the rock, on the side towards the ocean. That boulder completely blocked our cell reception. The only towers we could connect to were on the US side - 20 miles across the strait. One day Cathy tossed her cell phone into a giant china bowl that we had sitting on a table in front of the window. I'd say the bowl was 16" across... in any case, this bowl acted like an antenna, and as long as we put our cell phones in the bottom of the bowl, we could send and recieve calls. True story. Take that Moss Rock! :)
I don't know what kind of rock that thing is but it is an effective block to cell phone signals!