Well aren't square, weir boxes are though and I don't ever remember seeing a Silver or Gold mine looking like that, But an Intake filled with rock to keep fish out makes more sense to me.
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The top couple feet is square the rest of it is round. Definitely not an intake or weir. If I figure out how to post the video you will see.
O.k. cause wells are usually 16" Steel pipe, all the way to the top with a bolt on flange even if it is a submersible pump. Like Vic said those studs are a D.G.A. for a screen, Probably for an intake.
This is right where the old town of Mormon Island is located. More than likely this thing dates back to the 1800's.
http://en.wikipedia.org/wiki/Mormon_Island,_California
Here's a picture of my computer. This is down about 5 feet.
Attachment 30306
You need to find a historian now. ANSWERS
Here's a video that I filmed off of my computer, its really crappy.....the real video is much better quality. This was about the first 10-15 feet.
http://www.youtube.com/watch?v=9ISodO16NrU