Precambrian and Pleistocene Celebration – Mollman Lakes – Mission Mountains Wilderness
November 16, 2021
Summer was slipping into autumn when we clambered along Mollman Creek. The difficulty of this trail was ease be the company, including a lovable mutt named Bruno (and believe me the name is quite fitting). The views were consistently amazing, but the real star is the geologic story that was told by the landscape and rocks of this drainage. Looming above, Mount Calowahcan dominates the ridgeline.
The Trailhead
The trailhead is located NE of St. Ignatius, where the Mollman Pass Trail Road intersects Hwy 93. Turn east off of Hwy 93 and travel for 3 miles. Turn left onto Hammer Dam Road and follow for 0.5 miles. At the sharp bend, continue straight over the cattle guard onto a gravel road. Continue for about half a mile. Cross the canal and continue straight past the sign on a rough road for about a mile. We parked here and began hiking.
The Hike
The trail begins where the road ends (imagine that?), where we hiked under a western red cedar forest.
We worked upwards into meadows of the lower basin, through cliff bands, and finally into the upper lakes basin and the pass.
Good footpath that increasingly grows rockier and steepens as you near the pass. It’s worth exploring the area of the pass and beyond. Trail has no route finding challenges (the upper valley is quite overgrown), and is relatively strenuous. Plan on 12 miles round trip and about 3,600 feet of elevation gain, so your workout circles will be complete when you finish.
Now for the Pleistocene Geology
Imagine the landscape during the Pleistocene. Massive ice sheets descending southward over North America as they shape much of the landscape we hiked through on afternoon. 2 to 3 million years ago, the Mission Mountains already towered above the valley, the result of more than 100 million years of orogeny (mountain building) caused by the slamming together of the Pacific and North American tectonic plates. The immense ice sheets crushed, ground, and sculpted the lofty peaks into crags, knife-edge ridges, and deep, U-shaped valleys. Nearly every surface feature across this range – the mountains, streams, lakes, and rolling valley floors – is the direct result of the glaciation, and by extension, the ecology and habitats of the region and native plants and wildlife that reside here.
Commonly known as the Ice Age, the Pleistocene Epoch spanned nearly 3 million (we’re talking deep time here folks) and came to an end only 10,000 years ago. A massive glacier, known as the Flathead Lobe of the Canadian Cordilleran Ice Sheet, advanced several times south into the Mission Valley, ending its march near St. Ignatius. The Mission Valley itself the southern terminus of the Rocky Mountain Trench, an incredibly long valley, that stretches 600 miles from British Columbia. This massive frozen river covered the valley floor and reached a thickness of over 4,000 feet. It covered all but the highest peaks in Glacier National Park, and most of the Whitefish, Swan, and northern Mission Mountains. From the exposed alpine peaks, smaller glaciers flowed down from the heights and joined the huge tongue of ice.
The abrasive scouring of glacial ice created rugged topography of the Mission Mountains. The classic deep, straight, U-shaped valleys and knife-like ridges (arêtes, if you’re Franco-inclined), three-sided pyramidal peaks, and hanging valleys found in the Mollman Creek are all textbook examples of alpine glaciation. Perhaps the most unique geologic feature resulting from the Pleistocene glaciation are southward pointed, hook-shaped ridges at the end of each canyon on the Mission Mountains, which were created when the smaller alpine glaciers flowed out of the mountains and joined the larger one in the valley. Think about a small stream joining the flow of a larger river.
Onwards to Mollman Lakes
Crossing over Mollman Pass is like entering a lost world. You can intellectualize the fact there is a trail leading to this flat pass surrounded by the towers of Mission Mountains, but I swear to God that we were the first visitors to this subalpine basin and its lakes.
Let’s get old with the Precambrian
Making our way down the ‘middle” Mollman Lake, I noticed these large slabs of large rocks with the most unique texture with no discernible pattern to it. Remaining puzzled, I tapped Dr. Rob Thomas on Facebook to help answer my questions. These formations turned out to be uniquely formed Belt Supergroup strata.
The Belt Supergroup is dominated by fine-grained mudstones, siltstones, quartzose sandstones, and limestones. Most have undergone slight metamorphism of the mudstones as argillites and the sandstones as quartzites.
The majority of deposition occurred between about 1450 and 1400 million years ago. Many sedimentary structures such as ripples and mudcracks are well preserved in most of the Belt rocks despite their great age.
