This study determined horizontal positional errors when using C/A code GPS receivers under forest canopies and in varied terrain. Positional errors were evaluated for a total of 18 sites: three sites for each of six combinations of canopy (conifer, hardwood) and terrain (ridge, slope, valley). Ten replicates were collected at each site for each of 60,200, and 500 position fixes. Differentially corrected positional accuracies from conifer sites averaged 18.4ft, which was significantly greater than the 14.5ft Observed for hardwood sites. For differentially corrected data, positional errors generally increased from ridgetop to valley positions. - Errors decreased when the number of position fixes was increased.