Description of the ASCII gravity station listing, named
mtgrav.gz, a compressed file containing 40,671 stations
within or adjacent to Montana.

The fields are listed in this order:

Station identification; 8 digit numbers are from the Defense
Mapping Agency and the first four digits are their reference to
individual surveys; other stations are USGS or other sources.

Longitude, negative west, in degrees, decimal degrees

Latitude, positive north, in degrees, decimal degrees

Free air gravity anomaly, in milligals (mgals)

Bouguer gravity anomaly, in milligals, reduction density 2.67 g/cc

Elevation, in feet

Inner terrain correction zone, from 0 to .895 km radial distance, mgals

Outer terrain correction zone, from .895 to 167 km radial distance, mgals
(note: total terrain corection obtained by adding inner and outer
zones)

Observed gravity minus 980,000. mgals, in mgals