All Chaco trail GPS background images are in the following
projection:

UTM (Transverse mercator) 1983

Zone: 13

Spheroid: GRS 80

Central meridian: -105

Reference latitude: 0

Scale factor: 0.9996

False easting: 500000

False northing: 0

*Before using these trail map image backgrounds, you need to
change your GPS settings (in ADVANVED SETTINGS) to UTM (Universal Transverse Mercator, or Transverse Mercator). The
UTM Zone whithin which these trail backgrounds fall is called:
Zone 13. You may or may not need to do the Zone set-up in your
GPS; however if you do, there it is! The DATUM used for these 
backgrounds is of course NAD83 (North American Datum 1983).