[GRASS-user] Determining Datum From Projection Coordinates

[Rich Shepard]

   Context: I have a postgres table with > 110K rows of permitted wells.
Among the columns are lat, lon, utm_easting, and utm_northing; for example:

  latitude  | longitude  |  utm_easting  |  utm_northing 
-----------+------------+---------------+----------------
  41.040000 | 117.310000 | 473829.030000 | 4543648.900000
  40.980000 | 117.410000 | 465323.370000 | 4537116.040000
  40.930000 | 117.450000 | 462092.370000 | 4531365.620000
  40.890000 | 117.080000 | 492442.050000 | 4526893.330000
  40.890000 | 117.080000 | 492442.050000 | 4526893.330000
  40.910000 | 117.160000 | 485988.390000 | 4529277.070000
  40.920000 | 117.150000 | 487182.810000 | 4530107.450000
  40.920000 | 117.160000 | 485989.150000 | 4529677.930000
  40.970000 | 117.140000 | 488103.560000 | 4535409.570000
  41.650000 | 118.520000 | 373435.960000 | 4612467.900000

   Because these data come from a Nevada state agency I can safely assume UTM
Zone 11, but I'd like to determine if the datum is NAD83 (in meters) which I
suspect it is, or NAD27 (in feet). What is the most simple way of determing
the datum and units.

   Once I know the datum and units I'll learn how to associate these data
with GRASS. My purpose is to produce maps of the depth to bedrock and static
water level depth by county and basin. Since this is all new to me I need to
learn it one step at a time.

   All pointers, suggestions, recommendations, and other advice is welcomed.

Rich