Follow the "Getting There" instructions on the main page for directions to the Big Quilcene Trailhead (2500').
Depart the trailhead, sign the register, and follow the Big Quilcene Trail (#833.1) through the forest. You will pass through Shelter Rock Camp (3650') after 2.6 miles. Continue to the tree line and you will be passing under Iron Mountain (6826') and both the northeast (6956') and southwest (6988') summits of Buckhorn Mountain. You will also see the scree field that goes from the trail to the saddle between the the two summits of Buckhorn Mountain. Then you will re-enter a small alpine pine forest and pass through Camp Mystery (4.6 miles, 5400'). After Camp Mystery you will head up through a alpine meadow where you can often see the Olympic marmots and their dens. You will reach Marmot Pass (6000') where you intersect the Tubal Cain Trail (#840) and Dungeness Trail (#833.2).
View of Big Quilcene Trail Meadow below Marmot Pass Sign post at trail intersection at Marmot Pass
You can also access Marmot Pass via both the Tubal Cain Trail (#840)(8.6 miles) and Dungeness Trail (#833.2)(8.1 miles).
Looking towards the southwest summit (6988')
Leave Marmot Pass (6000') and head north along the Tubal Cain Trail (#840). Go about 100 meters until the trail splits. To the left you will continue along the Tubal Cain Trail. The right trail begins up the ridge towards Buckhorn Mountain. You should be able to see the trail heading up the spur and onto the ridgeline. You will follow the trail and switchbacks to the ridgeline. Go across the small knob (6800') and then on to the southwest summit (6988'). Upon summiting you can see to the east the northeast summit (6956') and then on to Iron Mountain (6826') further east. The topographic map identifies Buckhorn Mountain as the northeast summit and it appears that the USGS marker is there as well. You can then downclimb the east side (class 2-3) to the saddle between the two Buckhorn Mountain summits. From the saddle you can also access the northeast summit (see other route) or travel back down (carefully) the scree field to the Big Quilcene Trail (#833.1).
Looking up along the trail towards ridgeline.
Looking down towards Marmot Pass.
View of ridgeline connecting summit to Marmot Pass.
If the route is snow free addtional gear is probably not necessary to attain the southwest summit of Buckhorn Mountain. If you choose to downclimb the east side to the saddle and up to the northeast summit then depending on your comfort level with scrambling (class 2/3) and exposure you might want to bring a rope and helmet.
There are multiple camping opportunities that are close to allow a summit of Buckhorn Mountain.
Along the Big Quilcene Trail (#833.1) you can camp at Ten Mile Shelter (Mile 0.0, 2500'), Shelter Rock Camp (Mile 2.6, 3650'), Camp Mystery (Mile 4.2, 5400'), and Marmot Pass (Mile 5.3, 6000'). Water should be available from streams at Ten Mile Shelter, Shelter Rock, and Camp Mystery. Water at Marmot Pass is intermittent (snow or springs).
Along the Tubal Cain Trail (#840) you can camp at the Silver Creek Shelter (Mile 0.1, 3300').
Along the Dungeness Trail (#833.2) at Camp Handy Shelter (Mile 3.4, 3100') or Boulder Shelter (Mile 6.4, 4950').