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?
Unfortunately, you're not going to get negative coordinates using a state plane zone, unless the data is well outside the zone's defined area of use. The state plane zones (and UTM) were designed when doing calculations by hand or maybe on a desktop calculator. You didn't want to have to deal with both positive and negative values.
Thanks everyone. I did try everything with CA prefix, including all of the State Plane systems. The closest possibility turned out to be Projected State Systems NAD_1983_2011_California_Teale_Albers. However, the positions were still wrong. These are sample sites on CA trout streams, and the points ended up about 127 miles southwest of the streams they were taken from. I tried translating the entire group of sites northwest to see if they would line up on the correct streams, but no. So I think I have garbage data. I'm going to have to estimate from marks on poor quality paper maps. I do appreciate all of the feedback I received; it was very helpful and I learned a lot.