I've received a 1983 dataset from a California agency. The coordinate system is nothing I've ever seen before. Attributes say "North_GPS" and "West_GPS", and value pair examples are all similar to (-33471.539,159239.375) I've tried several different decimal meters coordinate systems, but nothing works. I know the actual locations should be on the east slope of the Sierras, so I'd expect to get coordinates in UTM NAD83 Zone 10 or UTM NAD27 Zone10. My data source agency has no idea. These pairs are especially weird since there is a "westing" instead of an "easting". Anyone have any ideas of what system these use?