This is the geology guide to the ‘back door’ trail to Excelsior Pass and nearby ‘Excelsior Peak’. For the description of the long ‘front door’ trail climbing out of the Nooksack River valley, go here. The Damfino Trail reaches open flower meadows at 5000′ elevation (1520 m) in 2 miles (3.2 km), Excelsior Pass in 2.75 miles (4.4 km), and the stellar viewpoint atop Point 5712′ (1740 m) in 3.4 miles (5.4 km).
Geologic highlights: the usual glacial till; a fine exposure of two volcanic ash layers: 7200-year-old Mazama Layer O from the Crater Lake caldera, and the 6800-year-old Mount Baker BA tephra; seafloor rocks of the Jurassic Nooksack Formation and its Wells Creek Volcanics Member. And, from the top, views forever.
Getting there: The Damfino Lakes trailhead is 15 miles up the Canyon Creek Road (FS 31) east of Glacier. Cross the North Fork Nooksack River 2.2 miles east of Glacier, pass the entrance to Douglas Fir Camp, and turn left on the Canyon Creek Road. Pavement ends at Canyon Creek in about 5 miles. Go right at the creek crossing. The road can be well-potholed beyond here; the lower your ground clearance, the slower it will be. Take a left in 2.25 miles (3.6 km) at the (subtly) signed fork with Rd 3160. Stay left in another 3.6 pounding miles (6 km) and climb the last 1.5 miles (2.3 km) to the cramped trailhead at 4277 feet (1300 m). The Northwest Forest Pass is required for parking.
Annotated geology map in Tabor and others, 2003, the best available geologic map of this area. Red arrow is initial path of Pleistocene ice from Canada. Green: Damfino Trail; red: Excelsior Trail; blue: Nooksack River. North is up. Squares are 1 mile.
The geology guide: The trail reaches the Mount Baker Wilderness Area boundary in about a half mile, and shortly after that the shallow pair of pools in the forest called Damfino Lakes at 4480 feet (1365 m). They are in the broad, relatively low elevation drainage divide between Canyon Creek, draining west to the Nooksack River, and Damfino Creek, draining north into Tomyhoi Creek and then the Chilliwack. The geologic map shows a broad swath of yellow glacial deposits (Qgu) running through the saddle. Back in the days of the huge continental ice sheets, tongues of ice advanced up river valleys south of the Fraser River as the ice sheet grew thicker in the interior of British Columbia. One tongue flowed southward up Tomyhoi and then Damfino Creeks, thickening and advancing as the main ice sheet did so. Eventually the ice could overflow the drainage divide here and reach tributary streams of the Nooksack valley. High Divide was too, well, high and so the earliest ice advanced down Canyon Creek until thickening continental ice could overtop higher passes on High Divide, first at Welcome Pass (5200′, 1585 m), then Gold Run Pass (5400′; 1645 m) and, eventually, the entire ridge, burying pretty much everything, filling the Nooksack, advancing up drainages north of Mount Baker, surrounding the volcano and then overwhelming the northern Cascades. But, another story. Here, I suspect you are in the first place in the upper Nooksack drainage to see continental ice. Of course, ice was also flowing out the Fraser and into the lowlands of the Salish Sea. Tongues of this ice flowed up the Nooksack, to join those entering from the north. So, a pretty significant location, these little puddles, even if they aren’t all that much now.
Anyway, continue up through the woods. Other than glacial till, not much to see until the meadows. After traversing the first, west-facing meadow, cross a stream on a big slab of Nooksack Formation shale. Climb on to an extensive, nearly flat heather-covered bench and watch very carefully for a volcanic ash exposure in the shallow trail side ditch. There are several possible places, but you are looking for a 1-2 cm thick layer of distinctive orange, very fine grained Mazama Layer O. The UTM grid location for the one shown below is approx 588253 m E, 5421448 m N (WGS 1984 datum). You will need a garden trowel or large pocket knife to clean off the profile for proper examination. If you go soon, you may be able to find my scrapings.
A nice tephra exposure 150 yards past the stream crossing.
Mazama ash was erupted from the Crater Lake caldera in southern Oregon 7200 years ago, 420 miles (675 km) to the south. (Geologists call it ‘Layer O’ in field notes due to the typical orange color, until the identity has been confirmed in the lab.) It drifted here in the huge eruption cloud that covered a large swath of North America, many times larger than Mount Saint Helens 1980. The Mazama ash is soft and very smooth- you don’t feel any grains when you rub it in your fingers, and barely notice any grittiness if you put a pinch in your mouth (seriously, try it). Only the smallest particles drifted this far, coarser clasts fell out well to the south. The thickness in this flat location is probably reflective of the actual amount of ash that fell here. The Mazama ash rests on soil, so it was not a barren rock surface. Compare it with the nearly half-meter-thick deposit in the meadow south of Excelsior Pass; that one is on a sloping surface and probably results from water flushing Layer O off the surface, whatever it was (snow? vegetation?) and redepositing it in a small depression.
Sitting on Layer O is the 6800-year-old gray ash from the largest known post-glacial eruption from Mount Baker. The BA ash here is about 2.5 cm thick. Despite the 400 year age difference, the absence of intervening soil suggests this place didn’t have much vegetation back then to decompose into soil. If you take a small pinch of BA in your fingers, you can feel its grittiness. The clasts that fell out of the BA eruption cloud only traveled 11.5 miles (18.5 km) to get here, so the fine sand-sized clasts made it this far. The eruption plume did continue north- the BA ash is 5mm thick at Spoon Lake in the Cheam Range, 17 miles (27 km) to th NNE. And this is also probably close to the actual thickness of ash that fell here.
Beyond the flats, the trail crosses a few rock outcrops that provide an excellent example of why you shouldn’t judge a rock by it’s cover (sorry!). Weathered surfaces are tan, but where the rock is broken you see that the fresh rock is dark grayish green. Exposure to rain and atmospheric gases alters the chemistry of the minerals in the rock; for a good explanation of the process of chemical weathering check out this Lumen Learning page. This rock looked to me like greenstone, formerly lava. Both Tabor’s geologic map (above) and my own observations show that the Jurassic Wells Creek Member of the Nooksack Formation is found here. I discuss those rocks in more detail in the Excelsior Trail page and also the Wells Creek Volcanics page.
The trail goes over this weathered surface; fresh interior rock is really obvious.
The trail reaches Excelsior Pass at 5370 feet (1635 m) and joins up with the Excelsior Trail. The rocks right in the pass are breccias in the Nooksack Formation.
Take a look at the outcrops in the trail at and around the pass. We are at the transition between the Wells Creek Volcanic Member and the sedimentary rocks of the Nooksack Formation. Like I said, there is no hard and fast dividing line between the two. The rock here is breccia, meaning there are angular rock fragments, or clasts in the surrounding sediment. These have been shown to be fragments of andesitic or dacitic lava, almost certainly derived from the Wells Creek Volcanics, tumbled onto the seafloor and mixed with finer grained sediment- perhaps a landslide or slump off a steep bluff of lava, at one time fairly near where these rocks were deposited.
Nooksack Formation at Excelsior Pass. Breccia has angular clasts. Conglomerate has rounded clasts. The first is indicative of a short travel distance between the source of the clasts and the deposit, not enough to round off edges. The latter indicates further transport, sufficient to round clasts.
From here on the trail joins with the Excelsior Trail description on the way up to ‘Excelsior Peak’, so I am just going to copy/paste that stuff here.
From the pass, take the trail to the east [that’s to the left coming from the north, signed ‘High Divide’] and stay right at the fork just a few steps away. Traverse meadows. Note that the trail tread is small gray chips, characteristic of Nooksack Formation shale. In a few hundred yards pass a prominent bedrock outcrop, the best seen on the whole trail. It is well-bedded Nooksack shale remnant of an ancient seafloor. Rowland Tabor reported radiolarian fossils of probable Jurassic age here. They are microscopic so don’t get too excited! The layers are tilted steeply, the consequence of subduction, uplift, and faulting; they dip 65° to the north (see the ‘Chuckanut Road’ field excursion for more on dipping rock layers).
300 yards east of Excelsior Pass, these trailside Nooksack Formation layers dip 65° north (to the left, more or less) . My friend Grace holds a flower for scale.
Round a corner and reach the crest of High Divide east of Excelsior Peak, then make a steep trudge to the summit, site of a long-gone fire lookout (1935-1968, then demolished). What a view! You are sitting on a hump of eroded Nooksack Formation; a fantastic 360° vista- west along High Divide to Church Mountain and Bearpaw Butte, north into Canada, (the prominent gray dome is Mount McGuire, a bare limestone peak of the Chilliwack Formation); east to peaks innumerable; and, of course Mount Baker, less than 12 miles (18.5 km) to the south. This is why people hike up here- not principally for the geology, I will admit.
West toward Church Mountain and the craggy Bearpaw…
South to “Mount Baker’s Gleaming Crest” and the snowy crest of Ptarmigan Ridge to the east (that’s left)…
East into the heart of the North Cascades…
North 6.5 miles (11 km) to Mount McGuire and the Cheam Range between the Chilliwack and Fraser River.
Northwest Geology Field Trips 