This mountain (one massif despite the plural name) has long been absent on summitpost. I'm not sure why, as it is a summit that would fit well onto the site: it is a popular objective, it is a superlative viewpoint, it can be skied, it has a lookout (a permanent tent-type lookout erected in 1931), and can be climbed in a reasonably short day. It is incorrect to call the mountain Hidden Lakes Peak, as many do. There is really only one lake of note. A small, shallow tarn a quarter-mile north of Hidden Lake could hardly be called a lake.
Hidden Lake Peak(s) is located wholly within the Cascade River drainage 14 miles east of Marblemount at the hub of where the valley makes a pronounced bend counterclockwise. Further, the peak lies on the border of North Cascades National Park. The approach and trail on the west side of the peak are not in the park. Hidden Lake on the east is within the park.
There are three "summits" for the mountain massif. The association of one of these is tenuous because it lies north of Sibley Pass (6,060 ft), the natural dividing line between the massif and the continuing ridge eastward to The Triad. However, the map shows the labeling for this peak extending to the northerly summit (Pt. 6480+). I personally wouldn't include Pt. 6480+ as one of the Hidden Lake peaks. The other summit is the southerly one (Pt. 6890) where the lookout is located. The trail goes to this summit. The main summit is Pk 7088 (1008P). A short, easy scramble and/or bootpath to the summit leads from the notch on the south. Alternatively, the peak can be climbed from its north ridge.
Hidden Lake (5,733 ft) lies in the cirque east of the main and southerly summit. The lake is quite large for the elevation and remains frozen over until late June or early July. A rough path continues from the 6,600-ft notch between the summits to the shores of the lakes. It is not unusual for people to camp at the lake. I'm pretty sure trout lurk in its waters.
There is only one approach worth mentioning and that is the one up Sibley Creek's East Fork WNW of the summit. All other approaches (from the Cascade River Road on the south or east) will be wholly cross-country cliff, gully, and steep forest climbing affairs and are therefore not worth it. Stick to the trail route.
To get to the Sibley Creek Trailhead, first find yourself in the town of Marblemount on Hwy-20 (North Cascades Highway). At the main corner in town, a road goes east across a bridge. This is the beginning of Cascade River Road. In maybe about 5 miles from Marblemount there is a viewpoint overlook on the right. Hidden Lake Peaks can be seen from this viewpoint (click here for that view).
At 9 miles from Marblemount Sibley Creek Road No. 1540 exits to the left and proceeds steeply up the drainage for about 4.5 miles to the trailhead (3,600 ft). Some of the road is quite rocky but a standard car can make it (at least currently).
Warning: This trail resides in a heavy avalanche zone. DO NOT venture up it if the danger is high.
Click here to obtain the latest avalanche forecast.
Take an ice-axe in early season. Some steep snow slopes should be expected.
The trail up Sibley Creek intially follows an old road before immersing itself in a forest band. At this point, it switches back and forth up the slope a number of times to finally emerge into the open for good. This is where it becomes scenic. The drainage and upper basin are beautiful...except for the trail itself as it cuts an unsightly "gash" up green slopes (especially when looking down the basin from above). The trail crosses to the north side of the creek and ascends some distance above it, switchbacking as necessary. In about 2.5 miles the trail reaches the head of the basin (c. 5,400 ft). At this point, about one hundred yards beyond where the trail begins contouring south, a bootpath winds its way up to Sibley Pas (6,040+ ft). It is not necessary to go to this pass to climb the peak, although it is certainly a feasible route. Most of the terrain is open country with the minimum of scrambling (Class 3 max).
From the head of the basin the trail continuance might be known as Hidden Lake Trail (this is what it is called on the map). The trail contours the northwest slope of Hidden Lake Peaks for about a mile before ascending once again in a final push to the 6,600-ft notch between the main summit and the south summit. A scramble path leads up to the lookout on the southerly one. A scramble path also leads north to the main summit. Yet another path leads to Hidden Lake to the east.
Alternate Route to Main Summit
It is not necessary to go all the way to the notch between the summits in order to climb the main summit. This is especially true in early season when the trail is covered anyway. For this route, contour the northwest slope (trail or snow) for less than a mile until at or just before the damped out western spur ridge is cornered. From here, simply head up slope, weaving through minor rock bands as necessary, to meet the ridge crest someplace north of the summit. The final scramble to the highpoint is blocky Class 3.
Time = 3 hours
Gain = 3,500 ft
Distance = 3.7 miles to the notch between summits + 0.4 miles along ridge to main summit; or 3.3 miles to main summit if using alternate route described above.
The trailhead requires one of those lame Trail Park Passes. You can expect patrolling to be moderate considering its close proximity to the Marblemount R.S. The east side of the peak lies within North Cascades National Park, so standard park policy would apply there. For instance, you'll need a permit to camp at Hidden Lake.
As stated in the overview, this peak (or at least the Sibley Creek drainage) is a popular ski objective. Since the trailhead is over 3,000 ft, you may be required to walk the road for a distance in winter and spring. For non-skiers, the trail is usually snow-free by July. In June one should expect to cross avalanche debris remnants (mainly in the creek bottom) and steep snow slopes (at the head of Sibley Creek). An ice-axe should be taken along.
Camping is feasible in many spots on the trail but the most scenic location would be at Sibley Pass. I suppose if you intend to camp on the east side of the pass you'll need a permit from a ranger station (nearest one located in Marblemount). This also goes for camping at Hidden Lake. Other than that, this peak can be climbed in a day easily so camping should not be necessary.
The Sibley Creek Trail is used as an alternate approach to Eldorado Peak, passing The Triad along the way. In this case, a camp at Sibley Pass might be more to your liking.