In short, the USGS 1:100K map shows a portage that starts much farther west than the portage we see. If you’re using Garmin’s maps, this might matter, particularly on the west (river) side.
As a reminder, moving west to east, after the Wheelbarrow Falls portage, there is an unnamed short portage (“little portage”), a short paddle, and then the Basswood Falls/Horse/Mile portage (“long portage”), which ends on Basswood Lake.
The 1:100K map shows one long portage that runs from the western side of the little portage to the lake. This map also shows the lake side of the portage ~100 feet to the west of its current location (i.e., too close to the falls for my comfort). As it is marked, the ground length is ~1.5 miles. As I measure it, the current long portage is ~1.1 miles.
The 1:100K maps matter because Garmin has built them into many of their GPS models and sells them separately as “Topo 2008”. (“2008” refers to the date Garmin published them and not the publication date of the maps they digitized.)
The most recent 1:100K USGS maps for the area are from 1994, which you can retrieve from USGS Historic Topo Maps.
The USGS 1:24K maps show where the actual long portage comes to the river and show a portage that starts at the western end of the little portage but which does not connect to the river and instead connects to the long portage less than 100 yards from the river. Garmin also sells 1:24K maps, but I don’t have them and don’t know what they show.
The Backroads Mapbooks Paddling Trails (“BRMB”) map does not show the little portage. Instead, they show two portages on the Canadian side that cover the same ground, one shorter than the other. (Maybe low and high water portages?) Fwiw, the BRMB maps show other border portages that are on the US side.