I've never heard of this trail before. But I'm going to ask around some.
Based on the comments in the NAXJA forum thread I think this is an illegal trail. They are talking about busting through dead brush or trees, using chainsaws to open other trails, the trail being brand new, and I see what appears to be cryptobiotic soil in between the tire tracks in some of the photos. It appears to be in the area at the south end of the valley, I suspect on SITLA property because they make mention of the supposed creater of the trail being the person who created Upper & Lower Helldorado & Upper & Lower Proving Grounds. All of those are on SITLA properties, and all but Upper Helldorado are now officially closed, & it would've most likely been closed if someone else had purchased the property.