Ran across this on advrider. Might be useful for someone planning a dual sport trip.
http://gravelmap.com/#@34.26463868715288,-87.79175675964359,9,hybrid (http://gravelmap.com/#@34.26463868715288,-87.79175675964359,9,hybrid)
"Gravelmap is an interactive database of gravel and dirt roads and paths, submitted and managed entirely by people who ride them."