GPS and American River

["Dorothy Joiner" <djoiner@countyofplumas.com>]

We rode the 30 mile ride at American River.  Just for fun, we decided to take our GPS and set the odometer mode so that we would know exactly how far we'd traveled.  The GPS and the mileage map were almost exactly the same...until the last 10 miles.  At that point, according to the GPS, we had gone about 2 miles further than where they said that check was (Rattlesnake Bar).  We chocked that up to going off the trail, down to the water, etc. 

 

However, when we got to the end of the ride, our GPS was reading 39 miles--not 30.  The folks we talked to there swore up and down that our GPS was wrong.  So we checked it in the odometer mode travelling in the car.  Its right on.

 

Any ideas what would cause a GPS to ADD miles?  I know they can sometimes cut them off if you don't have good sattleite reception--but add??

 

Dorothy & Elly

Butterfly Valley