I concur that low-range is mandatory. An aired-down 2WD vehicle could probably make it on many of the trails in the San Juans, if it weren't for the fact that 15% grades and low oxygen content at 10,000+ feet don't let the engine realize its full power potential (normally aspirated OR super/turbocharged). Many of the passes exceed 12,000 feet.

Vehicles without a low-range transfer case should not be present on 4WD trails, whether in the San Juans or in Moab. Logan- you might make it to Imogene Pass in your XC70, but I sure wouldn't want to be following behind you- up or down. You'll fry your tranny on the way up or your brakes on the way down. (And I can't believe you suggested that a Murano might consider attempting any trail in Moab!)