It's trail #238 which becomes 238A. The trailhead is on Forest Service road #81approximately one mile beyond the turn for Climbers Bivouac, trailhead for the "standard" route, Monitor Ridge. It's a 4 mile hike on trails 238 and then 238A to the base of the route.
There is no marked route here as on Monitor Ridge and Swift Creek. The route is right in front of you when you reach the end of the Butte Camp trail. Use your sense as to the lay of the land and "path of least resistance" in terms of steepness. If you stay in as much of a straight line as you can without wandering too far left or right you will eventually see the crater rim. On the descent use the southwest side of the Butte Camp butte as a guide to intersect again with the trail, compass bearing 235 degrees.
This route usually doesn't open until June. Crampons and ice axe should be sufficient. If there's any doubts about the weather take (and use!) wands.
If you have information about this route that doesn't pertain to any of the other sections, please add it here.