https://waterdata.usgs.gov/nwisweb/get_ratings?<options>

 <options>

     period      Return files that have been updated in the previous
                     "period" (hours) (default = 24)

                 If site_no is specified but period is not...
                     (default = infinity)

     format      Output format (default = rdb)
                     rdb  = tab-delimited output
                     html = HTML page with links to each file

     agency_cd   Agency code for site (default = USGS)

     site_no     USGS site number to match
                     (default = all site numbers)

     file_type   Type of file (default = all file types)
                     exsa = expanded-shift-adjusted
                     corr = data corrections
                     base = base rating

     nws_hsa     National Weather Service "Hydrologic Service Area" office

     help        Display this text

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  NOTE: The normal return from get_ratings is a list of products that meet
  the entered specifications using the specified format, or an empty list
  if no products meet the specifications. However if ONLY agency_cd,
  site_no, and file_type are specified the list will be bypassed and the
  specified product will be returned directly.

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waterdata