I have a new Etrex 30x and am trying to get maps of North Carolina onto it. I have use BaseCamp and have created a simulated route, but I can not seem to figure out how to get it onto my Etrex along with a map that shows elevations , roads and rivers.
I also do not understand the different extensions (.img, .gpx, etc) and which work on the Etrex.
.img files are maps, such as the ones on this site
.gpx files are user data, such as your tracks, routes and waypoints
Creating a route has nothing to do with the map, your user data is completely separate and can be displayed on any map. However, if you want the GPS to give you turn by turn directions that follow the roads, then the map you use must be "routable". Routable maps must be constructed in special way, and there are almost none of them on this site.
There are a couple tutorials on this site to help you install maps. First, download the map that you want. Then follow this tutorial to install it in Basecamp on your computer
https://www.gpsfiledepot.com/tutorials/how-to-open-maps-in-garmin-basecamp/
After you get the map into Basecamp, use this tutorial to send it to your GPS. Unfortunately, these tutorials are a bit out of date so there are some differences in the current Garmin software
https://www.gpsfiledepot.com/tutorials/how-to-load-maps-on-my-garmin-gps-unit/