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People have been trying to sound the alarm for decades. Here's a picture from 1977 demonstrating how far the land in the California central valley had fallen i

• benj111 7y ago
  How did they measure that, out of interest? Theodolite to measure the surrounding hills?, how can you be sure those hills aren't subsiding? Compare to other hills?
  • vhold 7y ago
    I'm not sure, I did some searching. Here is an article that contains some technical detail. https://www.xyht.com/surveying/subsidence/ https://www.xyht.com/surveying/subsidence/ "As a point of clarification, the sign Dr. Poland is holding says this is the change detected in BM S661. However, according to the NGS datasheet for that bench mark (PID GU0103), it was not set until 1942. I have been told by reliable sources at the USGS that the pre-1942 subsidence, back to 1925, was a linear estimate. " This appears to be the data sheet for the bench mark used. https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=GU0103 https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=GU0103 Here is a recent analysis from 2018 regarding that area, the photo, and the data used. http://www.itrc.org/papers/pdf/subsidence.pdf http://www.itrc.org/papers/pdf/subsidence.pdf Which seems to conclude that the photo is possibly very wrong, they include a new updated photo at the bottom that only goes back as far as there is reliable data.
    • benj111 7y ago
      Great thanks. I had a look and couldn't really find anything either, you did better than me!