protips:
bing maps - shows what roads are gravel/dirt/unpaved in light brown (this is the only thing bing is good for)
google maps - turn on bicycling and terrain and they will show unpaved roads in dark brown and cycling paths in dark green
open street maps - use "outdoor" or "bicycling" versions of OSM and they show all kinds of trails in differently colored dashed lines. the best way to see them is on ridewithgps
Gravel Road Maps and Biking Routes - Gravelmap - look for yellow stuff
https://openmtbmap.org/ - explains itself