This is a very popular mountain biking area. Please stay alert while on the trails and be respectful of other users.
This 4x4 road leaves from 191 and heads gradually uphill, eventually reaching HWY 313. Along the way, you'll encounter beautiful rock formations, a detour for Gemini Bridge itself, and typical desert shrubland.
The lower section - from Highway 191 up to Arth's and the actual Bridges - is very steep and sandy, but is useful as an exit from the midpoint of Mag 7, to avoid the Portal exit.
The upper section from there to Highway 313 is not recommended at all; use Getaway instead. This part of the road gets a lot of high-speed jeep and motorbike traffic, and is heavily used by oil mining trucks.
Note that this road has absolutely no respite from the sun. If you do run this, wear sun protection and carry a lot of water. Most just use this to connect other trails.