Koppen Mountain Trail is a 7.4 mile out and back trail located near Cle Elum, WA that offers scenic views and is rated as difficult. The trail is primarily used for hiking and trail running and is accessible from July until October.
From Seattle drive east on I-90 to East Cle Elum, exit 85. Cross over the freeway overpass and turn right (northbound) on State Route 970. Cross the Teanaway River bridge, and in another mile turn left onto Teanaway Road. Drive north on the Teanaway Road, veering right as it becomes first the North Fork Teanaway Road and then unpaved Forest Road 9737 at 29 Pines Campground. Drive 4 miles to Beverly Campground and then continue on to Forest Road 9737-120. Turn left and follow it to the abandoned De Roux Campground and the trailhead.
Sunday 9-4-2016: My wife, a friend, and I hiked to Koppen Mountain (Elevation 6031 feet). We arrived at De Roux Campground/Trailhead around 10 am. The last 6 miles of the forest road 9737 are not paved but are in pretty good condition except for some washboards and small potholes.
From De Roux Trailhead, we took Boulder De Roux trail #1392, De Roux Spur trail #1392.1, then Koppen Mountain trail #1225. The first 1.4 miles on Boulder De Roux Trail along De Roux Creek is very gradual. The sound of creek is pleasant. At the trail junction we took left to De Roux Spur trail. The next 1.2 mies on De Roux Spur Trail climb 900 feet. At the saddle we took left to Koppen Mountain Trail. There were some downed trees on Koppen Mountain Trail, but all were manageable one way or the other. The final half mile to the summit is very steep, 30% grade according to my GPS track. For reference Tiger Mountain Section Line is 30% grade. Mailbox Peak old trail is 40% grade.
Black huckleberries along the trails were ripe and yummy. These trails are shared with equestrians, mountain bikes, and motorcycles. So some parts of the trails are deeply rutted. And you must be careful not to step on horse droppings. Fortunately we did not encounter any horses, mountain bike, or motorbikes.
We reached the summit of Koppen Mountain in 2 and a half hours. The temperature was 54 degrees when we arrived. It went up to 60 degrees when the sun came out. We had all kinds of weather, cloudy, sunny, a passing light shower, and even thunders. We had a pretty good view at the summit, but the top of Mount Stuart was coved with clouds all day.
As with several other trails in the area, the views the Stuart Range are excellent. The first half of the trail along De Roux Creek was very gradual and not much to look at. The short side trail to Koppen Mtn was steeper but not too bad and offered several nice overlook views along the way. Several patches of snow on the trail the last half mile so hiking poles would have helped. Almost no bugs on my hike but I highly doubt that is the norm.
The turn on to trail 1225 (Koppen Mtn) from trail 1392 at the top of the ridge is not marked so it can be a little confusing. When you get to the ridge line just head left onto a narrow trail and don't continue down the other side of the ridge). I also ran into a 15 ft snow wall 1/2 mile from the top but was eventually able to pick up the trail by taking a left.
Maybe not as nice as the nearby Lake Ingalls trail but still some beautiful views and not very crowded.