The California Topo 2011 shows up on Basecamp just fine.
The topo file appears to load onto the 128 GB micro SD card in the Montana 610, but then the topo map does not appear on the list of maps available on the Montana 610.
I've deleted and reloaded the topo twice.
What am I doing wrong? :o
Okay, after days of trying everything... I found the problem.
The Micro SD card was too big. I found another forum that advised that 64 GB is the max size.
So I took out the SD card and uploaded the map to the internal memory and now it works!!
Yay!
Hope this information helps someone else. 8)
Glad you figured it out. To be a little more specific, you must format cards as FAT32 to use Garmin's devices and that old filesystem is not compatible with 128gb cards. Honestly, a 32gb card is all you should ever need. The Montana has another technical limitation related to how many map tiles it can access. You will likely pass this limit long before you install 32gb of maps. :)