Elevation: 6,336 ft
This Grand Slam peak is not in the book. There are four routes listed below in order of popularity. All four routes involve steep Class 2 hiking. Updated June 2019
Mount Heinen is located in the Boise Mountains, in the Boise National Forest, about 4 miles north-northwest of Arrowrock Reservoir. This peak is one of the four peaks of the Grand Slam Peaks, the other three peaks are Kepros Mountain, Cervidae Peak, and Shaw Mountain.
Mount Heinen is the tallest of the Grand Slam Peaks. It is a great early season hike, but it is a strenuous climb from any direction. There are four routes outlined below. The standard route, the North Face Route, the Southwest Ridges Route and the Orth / Koehler route.
USGS Topos: Dunnigan Creek, Arrowrock Reservoir NE, Grape Mountain
Access begins at the point where FS-327, [(C) page 154] The Middle Fork Boise River Road leaves ID-21. This junction is 6.1 miles north of the the Lucky Peak dam. The junction is signed for Atlanta, Idaho. Follow this paved road along Lucky Peak Reservoir to Arrowrock Dam. The pavement ends just short of the dam. Set your odometer to zero at the top of the dam.
0.0 Arrowrock Dam. The road along Arrowrock Reservoir is narrow, washboard gravel with many blind turns and significant dangerous drop-offs. On weekends traffic can be high, Drive slow and responsibly.
0.7. Unnamed drainage. The Trailhead for Southwest Ridges Route.
1.4. Cinch Creek. Second Trailhead for Southwest Ridges Route.
7.5. Irish Creek Boat Ramp and the Standard Route trailhead.
9.0: Cottonwood Creek Road, FS-377 Junction. Turn left. This road’s condition varies from year to year. In 2019 it was in good condition with only a few rough spots. High Clearance recommended.
9.9: Cottonwood Guard Station.
15.0 Cottonwood Creek/South Fork Thorn Creek Pass, elevation 4,848. Park here for the North Face Route.
Standard Route: Southeast Ridge (Class 2)
The route starts on the northwest side of Arrowrock Reservoir. Park just north of the Irish Creek Boat Ramp. This route was originally a motorcycle track but is now designated for foot traffic only. The track can be viewed from this spot as it climbs up the steep slopes to the west. Follow this track upwards and to the northeast toward Point 5402.
The route now follows an overgrown fire break until just south of Point 6137. Traverse around Point 6137 and then continue north along the ridge that leads to Mount Heinen. This is a long, strenuous route. Take lots of water. Since I first climbed this route in 2000 a use trail has been beat in for nearly the entire distance. The route is roughly 10.0 miles with 3,500 feet of gain round trip.
North Face Route (Class 2)
This route is a little shorter, 9.2 miles, than the Standard Route and has much less elevation to gain with only 1,625 for the climb and 264 feet on the return. Nevertheless, it still includes a steep, difficult 900 foot section up the north face.
This route leaves FS-377 at the top of the North Fork Cottonwood Creek/South Fork Thorn Creek Pass. The route utilizes the FS-202 road system, a group of closed logging roads. The road is not well mapped on either the Forest Service or USGS maps as it includes a number of roads not shown on the maps. FS-202 and 202C are in good shape though 202C has brush encroaching on the tread in places. Unfortunately, none of the roads have signs designating which road is which. While I have hiked this route I highly recommend using a mountain bike for the first 3.6 miles.
Follow FS-202 west from the pass past the gate for 0.4 miles to a junction. Go left. The road now winds in and out of drainages to the ridge top where it turns south. Roughly 1.9 miles from the pass there is a Y-junction keep right and you will immediately come to a second Y-junction. This junction is the beginning of FS-202C. Go left.
FS-202C quickly wiggles its way steeply up the ridge, staying on the east side at first and then crossing to the west side between Point 5710 and Peak 5740. Once past Peak 5740 the road stays on the ridge top until it reaches Point 5645 at 3.6 miles. From this point the road drops into the saddle below Heinen’s north face losing 200 feet. While this section is rideable, I leave my mountain bike at Point 5645.
From the saddle, 5,444 feet, the trail steeply climbs to the peak’s lower eastern summit. This section of trail appears to be an old fire break which is occasionally traversed by elk and the occasional human. The trail is brushy in spots and always steep as it climbs up the face. As shown on my GPS track it is possible to leave the trail short of summit ridge and traverse directly to the summit. Round trip is 9.2 miles with 1,900 feet of gain.
Southwest Ridges Route, Class 2
This route (or routes) is the longest route discussed on this page but it has two advantages over the other routes. The first advantage is that it starts near the Arrowrock Dam and thus, the driving approach is much shorter. The second advantage is that it is less steep than the other routes.
There are two ridges that run on either side of Cinch Creek that climb more gradually than the Standard Route up to Heinen’s south ridge. John Platt suggested the route and along with Dan Robbins and four others we climbed up the ridge on the west side of Cinch Creek and descended the ridge on the east side. This was in 2007 and none of us were carrying a GPS. I estimate the distance at 12.0 miles with 3,500 feet of gain round trip. See John’s trip report which is linked below.
There are two parking options as shown on John’s map below. After Passing the Arrowrock Dam you can park at the first intermittent flowing drainage you encounter or you can proceed on to Cinch Creek which is the a major drainage that is difficult to miss. See the map below.
Both ridges are classic ridge walks with good game trails for much of the distance. The ridge on the east side of Cinch Creek is the shorter route at around ten miles. If you climb the ridge on the west side you will encounter a thick forest in the saddle between Point 6060 and Heinen’s south ridge. This area will hold snow longer than most points along the route. Whichever ridge you climb your goal is to link up with Heinen’s south ridge on the north side of Point 6137. From there, follow the Standard Route to the summit.
Orth / Koehler Route (Class 2)
Brian Orth, Toni Orth, and Abe Koehler hiked this alternative approach to the summit.
Brian describes the climb as follows: “We were also going to go up Garden Gulch, but it has a no trespassing sign at the bottom of it, so we headed up the wrong ridge on Wood Gulch instead. We figured the route out on the way down.”