Distance: 13 km (variable)
Elevation gain: 825 m (variable)View mapDownload GPS track
This is an early season hike that has many options, making it a suitable hike for anywhere from 2.5 hours to a full day. Be forewarned, however, that the trail - at least the portion heading to Grass Pass and the immediate area - is frequented by horseback riders, rendering it muddy and covered in horseshit. With limited options in the early or late hiking season, however, it is a decent place to explore.
The trail starts just east of the Sentinel parking area on highway 541. After parking, head back out to the highway using the shortcut at the east end of the parking area. Follow the trail east on the south side of the highway for about 20 m, crossing to the north when it fades. After another 20 m or so the trail curves onto an old road heading north into the forest. It's impossible to miss. From this point you will ascend roughly 400 m over 3 km, reaching Grass Pass in about an hour.
Grass Pass is where the options start. Initially we headed roughly south, following a trail out along the broad hillcrest that had been to your right (east) on the way to Grass Pass. After about a kilometer of level travel, reach a nice viewpoint, sometimes referred to as Boundary Pine lookout. Looking roughly northeast grants you a view of the Bull Creek Hills, a series of rolling hills that represent option two.
While there are cross country options to reach the hills from the lookout, the easiest way for the unsure to head up to Bull Creek Hills is to return to Grass Pass and take the trail heading northeast up the grassy hill. This trail reaches the first highpoint after about a 100 m ascent, dips about 50 m in trees, then ascends another 200 m to the top of the first Bull Creek Hill. From here it is easily possible to continue to the next few hills, but as we were exhausted from breaking trail through heavy snow for most of the day we decided to stop at this point.
Other options from Grass Pass we didn't attempt include heading north through Grass Pass - this didn't seem that appealing as the route appeared to be mostly treed - or climbing the ridge on the left (west) side of Grass Pass and working your way down to Gunnery Creek and exiting via this route. Descriptions of this are available elsewhere.