There are a few instances in which it will be necessary to perform a master reset on the Montana, including the following:
Performing a master reset can cause data loss. To back up user data* utilize the FAQ “How do I back up user data from my outdoor GPS with a USB interface?". If removing user data is desired to eliminate corrupt data or free up additional space, reference the FAQ “Why does my Garmin outdoor or fitness GPS still show my GPS data after a master reset?”.
To perform the master reset:
The Montana is now reset and ready for use.
*User data consists of waypoints, routes, tracks, and geocaches