As of May 2016 the AT crosses this road half a mile from the locked gates at the end. There is a small parking area before the gates, which are placed directly before a metal grate bridge that is starting to decay badly enough to merit not crossing it with a vehicle. As of this date the wooden bridges on the road prior to the gate were intact, but there were noticeable signs of wear on at least one bridge so if it has been a few years since I wrote this comment do check any spots that appear sketchy BEFORE crossing them. The advantage of taking this route is that it is a mere 2.6 miles to the top of South Crocker from the road, whereas it is 5.2 miles just to get to the top of North Crocker from the highway trailhead. The Caribou Valley Road is clearly recognizable by the Plum Creek sign a short distance in from the highway at the highest point of land. If you pass by a power substation on the left as you go northwest you have driven past it.
Thanks for the update!