Yes, Gaia GPS works offline.
1. Download Maps
Gaia GPS lets you download maps directly to your device.
Downloaded maps save locally to your device for offline access.
Be sure to download maps before you go on a trip, while you are connected to the internet:
2. Use GPS
GPS-enabled devices connect to positioning satellites to determine your location.
Your device does not need an internet connection (cellular or wifi) to provide GPS data to the app.
These articles will show you how to configure your device's GPS location settings: