After I loaded Garmin TOPO U.S. 24K West and then Southwest onto my GPSmap 60Csx with Basecamp, there are NO map detaisl. No roads, rivers, trails, nothing.
What may I have done wrong, and how can I do it right?
Have you set your detail level to more or most?
Menu>Menu>Setup>Map>(Arrow left to the "N")>Set detail to More or Most.
We don't support Garmin products here, so if my suggestion doesn't work you may want to post your question here: https://forums.garmin.com/forumdisplay.php?f=179
With the 60csx, you need to select portions of BOTH maps in Basecamp/Mapinstall and send them together in a single bundle. Your unit doesn't support multiple map files like newer Garmin products.
Are you sure you did this correctly? Press Menu > Menu > Setup > Map then scroll over to the (i) symbol. What maps are listed? What maps have a check mark in the box?
If you first sent the 24k map, then sent the Southwest map, it would have erased the 24k map and that might result in a blank screen, depending on where you look.