This is ‘Layer O’, erupted from during the cataclysmic collapse at Crater Lake caldera in southern Oregon, and 7200 years old. A particularly good one is at about N48° 30.470′ W121° 12.182’I don’t know which ash came from which volcano, except for the thickest, very fine-grained orangish layer at the bottom of the sequence. In a few places the trail cuts reveal layers of volcanic pale ash between dark soil layers. There is also some white, squarish potassium feldspar. The prominent dark minerals are biotite mica there is also white and clear plagioclase feldspar, and smoky quartz. The rest of the trail is in the granodiorite. The white crystals are mostly plagioclase feldspar Hiker guide to the geology of the Hidden Lakes Trail The Mount Baker quadrangle would suffice for all the rocks on this trail, except that the description of the Hidden Lake stock (the granodiorite that underlies the peaks) is described in much more detail in the Sauk River pamphlet, page 16.The trail is shown on the Eldorado Peak and Sonny Boy Lakes 7.5 minute topographic maps. Your proficiency in geology may be tested, but it is useful information. They come with a technical pamphlet that describes the many rock units- don’t be afraid to try them out. The lookout at the end of the trail is on the Geologic Map of the Sauk River 30- x 60-Minute Quadrangle. Most of it is on the Geologic Map of the Mount Baker 30- x 60-Minute Quadrangle. Geologic maps: The area lies on the margins of two USGS geologic maps. The Washington Trails Association (have you joined yet?) has a trail description and a history of the lookout again, no geo. The North Cascades National Park website has a detailed trail description– but no geology. It was in pretty good shape when I drove it in June 2015 and there were some much less rugged cars at the lot. The road is moderately steep, can be pretty rough, and is prone to washouts. Park smart and leave room for people to turn around. Drive 4.5 miles to the small trailhead (3680′). Drive 10.2 miles and go left onto USFS Rd #1540 up Sibley Creek (signed “Hidden Lake Road”. At the east end of ‘downtown’ turn up the Cascade River Road. So you might end up with a bivouac among the rocks.Ĭlick to enlarge map and any other images. Jagged boulders surround the building, and camp spots at the lake are a ways below you. If you don’t get to the lookout early enough to claim the bed, it is a long way to the next suitable sleeping spot unless you have excellent negotiation skills. If you want to sleep over in the lookout, it is first-come, first-served and you’ll need an early start on the weekend, or maybe on pretty much any other summer day. The trail is 9 miles round trip, and gains 2900′ elevation. Go for the view, sure, and the exercise but keep your eye on the rock, too. Geology along the trail is beautiful and varied- metamorphic schist of the basement, 75-million-year-old intruding granitic rock rich in crystals, younger dark andesitic dikes that invaded the pale granodiorite, and overlying volcanic ash deposits sandwiched between buried soil layers. The restored fire lookout at the end of the trail is perched on a narrow fin of rock with great vistas into the glaciated heart of North Cascades National Park: Hidden Lake nestles just below in a granitic cirque the ice-mantled peaks of the Eldorado-Forbidden-Johannesburg group dominate to the east. The trail up to the Hidden Lakes Lookout is among the premier hikes in the northern Cascades.
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