daydreaming:
For me, the most helpful of the maps found on
the Arch Harris site are the four .png format maps next to the description "Four overlapping maps, with campsite and portage symbols superimposed..." But they are huge files, and I'm not certain that they are a very efficient overlay for a handheld GPSr... more than likely they would slow things to a maddening crawl. I've done it with smaller map files, but never with those. If you'd still like to try, save them to your Mac, use your favorite image handling software (GraphicConverter?) to save the .png files as .jpg files, then follow the
instructions from Garmin to create custom maps.
If it is campsite waypoints and portage tracks you are after (this is the real gold mine here, I'd say):
1) Right-click and save the bwca-portage-tracks.gpx file to your Mac (the one next to the description "Portage tracks for all of BWCA...") It will save as a .xml file, for some reason. Delete the .xml extension from the file name to make it a true .gpx file. Double-clicking it should open BaseCamp and add its 920(?) portage tracks to a new On My Computer listing. Rename the listing in BaseCamp to something other than "Recently Imported from bwca-portage-tracks.gpx" before the next step.
2) Right-click and save the bwca-camp+port-wpt.gpx file to your Mac (the one next to the description "Waypoint listing of all BWCA campsites and portage endpoints...") It will save as a .xml file, for some reason. Delete the .xml extension from the file name to make it a true .gpx file. Double-clicking it should open BaseCamp and add its 2,098 campsite waypoints to a new On My Computer listing. If you'd like, you can also highlight all of these campsite waypoints then Get Info and change the small dot icon to the little pup tent icon, and also delete the 'CAMP-O' comment in the comment box. This file also has endpoints for all of the portages which I find annoying to have around (not to mention the silly little airplane icons). Delete those waypoints from your collection... they seem pretty redundant, given the portage tracks above.
Then, you are ready to send all of -- or a subset of -- your new data to your GPSr.