mattno3, You have a couple of options to accomplish what your after. Seldom posted one of the option I was going to suggest. I did look at the LBL website and the trails you are questioning.
As Seldom said, open in Google Earth -save as a .kmz file - use GPSBabel to convert .kmz to a .gdb or .gpx file - open the newly converted file in Mapsource or Basecamp and transfer the tracks for the area you are interested in to your GPS. Or you can take the .gpx file of the tracks to create a custom map.
I saw where LBL has the trails in a gis data file. From this you can create a custom map of the trails per the intructions on here.
edit: There is another opiton for you to get the trails into a usable .kmz file. That is fairly easy. Open the original .kml file in GE and take a screen shot of the entire trail system and save it as a .jpg file. Use what ever program you want to to crop the .jpg file as needed to have just the trails (you can do this with something as simple as MS Paint). Reopen GE and ADD - Image Overaly (your newly saved .jpg file) and geo-reference it in GE; (Putting the .jpg trails on top of the .kml trails). Save the geo-referenced file as a .kmz file. Now this file can be copied and pasted to your GPS and it will give you map of all the trails including the satellite imagery for that area. I checked the pixel size and file size using just a single .jpg and both will be ok.
Note: I just did this in about 15 minutes and tested it on my Oregon 450, since the area in question is only about a 2-3 sq. mile area you are able to use just a single .jpg for all of the trails and the map will 1st appear on your GPS at zoom level 1.2 mi. and still have decent resolution down to zoom level of 500 ft., below that the resolution is poor.
I did this just playing around not trying to Hi-Jack a map you might like to put on GPSFileDepot. I'll be glad to send you the useable .kmz file, or upload it on here if you don't want to, or walk you through the process so you can upload it here; whatever you prefer. Also note from what I was seeing their trails look to have a pretty high level of accuracy, this .kmz map I did was just quick and dirty so not as accurate but still accurate enough for ATV use.