Sunshine Mountain is sequenced with UN 13,093. One-way mileage and elevation gain are measured from the summit of UN 13,093. Round-trip mileage and elevation gain assume completion of the sequence.
From the summit of UN 13,093, drop down to the east saddle on talus, followed by a tundra bench area, then followed by more talus. Once you arrive at the saddle, from there on, most of the hiking goes easily on mostly tundra and grass. From the saddle, hike uphill to the east gaining about 140 - 160 feet in elevation, then turn NE on mostly tundra with a few rocky outcrops thrown in. You can either gain the previously mentioned elevation or try to contour and side-hill your way to the next saddle. From that saddle, head east, then SE to obtain the summit of Sunshine. This too was over mostly grassy slopes that weren’t too steep. As you near the summit, the ridge narrows and becomes rockier, but overall, gaining the summit is easy and pleasant. From this quad summit, you can look down into a basin to the northeast (North Fork of Henson Ck.) and if you're lucky, spot some elk.
To descend and return back to your parked vehicle, we hiked back to the west about a mile and a half to the saddle just east of the 13,093 summit. From this saddle, we decided to take our chances and drop south into a steep basin that emptied out near the Rose Cabin. The descent took us on a traverse to the southwest, down a steep slope covered with loose scree, then another traverse across a broad ridge before connecting with an old mining road that descended on the west side of the unnamed creek that comes out and crosses the road just west of Rose Cabin. In places, this road almost disappeared, but for the most part, we followed it down the steep valley without difficulty. At 11,600 ft., it switchbacked, then again at about 11,400 ft. After this last switchback, the road headed down to the west until it finally intersected the Engineer Pass road at the 11,000 ft. contour. From here, it was a 3/4 mile trudge back up CR20 while numerous vehicles passed by stirring up plenty of dust. At least this way, you don't have to go back up and over UN 13,093, then Dolly Varden before descending.
Links to other information, routes & trip reports for this peak that may be helpful.