This is the route we took up the mountain. It is an easy route, but is perhaps not quite as easy as the route from the north. From the West Fork of Rock Creek Trailhead, the route follows the West Fork Rock Creek to the Lake Mary turnoff, follows the trail to Lake Mary and then climbs the steep southwest slopes to the gentle south ridge and thus to the summit.
This route is about 15 miles round trip and can be done in one long or an easy 1.5 days.
Kessler on a gentle section of Grass Mountain.
From the south side of Red Lodge, look for “West Fork Road” which heads west from Highway 212. West Fork Road is not far north of the Ranger Station and close to the Yodeler Inn. One on the west Fork Road (Forest Road 71), stay on the main road and follow it for about 14 miles to the trailhead. This is a good gravel road.
This is the last obstacle on the climb of Grass Mountain.
From the trailhead, follow the well worn trail up the West Fork Rock Creek. The first half of the trail to Quinnebaugh Meadows follows a burnt our forest from a fire in 2008. The trail passes Calamity Falls and Sentinel Falls which are worth a quick stop. After 4.2-5.0 miles (depending on the source) you will reach a junction near Quinnebaugh Meadows. The right (west) spur trail heads towards Lake Mary.
Turn right on the Lake Mary Trail and follow it uphill (some route descriptions have said the climb is brutal, but it really wasn’t bad) for 1.7 miles to Lake Mary which is right at timberline. From Lake Mary, scan the slopes of Grass Mountain to the northeast. Next to where the rockslide meets the grassy and forested slopes we found an old trail, but it is hard to find the beginning. If you don’t find the old trail, just head up the slope.
If you can find the old constructed trail, follow it up the slope. Since the slope is steep, the old trail does help. I assume that this is part of an old route to East Rosebud. The old trail suddenly fades away in the end just like it does in the beginning so just head up the slope the ridge.
Once the top of the steep slope is reached, the ridge becomes somewhat defined and the slopes become more gentle. From here, follow the wide ridge to the NNE to the summit, keeping the steep west slopes of the mountain to your left.
On the return trip make sure to not get sucked heading too far east as the gentle slope will try to guide you that way if you aren’t paying attention.
There is only minor boulderhopping and scrambling on this route. The top of the mountain is a rock pile that makes a fun scramble to the top.
Climbing Grass Mountain on August 28 2009.
Normal hiking gear and a good pair of boots is needed. Don't forget the map and/or GPS/compass.