Update 8/8/19: Warren Wagon Rd./FR 21 is now closed, which makes the proposed detour unrideable. Here is the closure announcement:
https://inciweb.nwcg.gov/incident/article/6496/50191/If you do choose to ride the Secesh Singletrack Option, which we can't wholeheartedly recommend based on current wildfire danger, here are a couple trails south of the Warren Wagon Rd. that could be used to close a shorter loop variation:
Duck Lake Trail (purple on attached map):
https://www.mtbproject.com/trail/7011767/duck-lake-trailCCW: From turn G (mi 22.
, turn left onto Tr. #084 passing Loon Lake and following Loon Creek upstream. In 11.4 mi., rejoin Secesh Option on Twentymile Tr. #085 directly north of Duck Lake.
This trail is rated a moderate singletrack with 2200 ft ascent, 1500 descent due largely to the ridge that must be negotiated at the head of Loon Creek.
Victor Creek Trail (green on map):
https://www.mtbproject.com/trail/7017932/victor-creek-trail-117CCW: From turn I (mi 24.0), at 3-way fork, turn left onto Victor Creek Tr. #117 and follow Victor Creek upstream. The trail is 10.8 mi total, moderate for the first 7 mi., then steepens as it ascends Diamond Ridge, at which point it begins the descent to Warren Wagon Rd./FR 21 (south of the closure area).
This trail is rated as difficult singletrack with 2200 ft ascent and 2100 descent, but is noted for high scenic beauty.
Note that ACA has not scouted either of these trails, so use at your own discretion.
Nathan
ACA Routes and Mapping