Actually, there are some awesome MTB/eMTB rides in Colorado and Utah that are on "dirt roads". Almost all of the original MTB rides in Moab, the ones that made it famous, are on what are considered to be "dirt roads". Porcupine Rim, Amasa Back, Gemini Bridges, Hurrah Pass, Poison Spider, Klondike Bluffs, Monitor and Merrimac, etc. Even Slickrock is actually a motorcycle trail, and the parallel 4x4 trail called Hell's Revenge is considered to be a "dirt road".
In CO, the 4x4 roads west of Central City and above St. Marys are fun.
Gnarly 4x4 roads are awesome on an MTB and an eMTB makes them even better. Less pushing.