Cutthroat Lake Trail in Washington state’s North Cascades takes you through all sorts of incredible scenery in the high mountains. It’s great on a hot day. It’s also a fantastic place to see a lot of colluvium in a bunch of different forms. Not only that, but you are rewarded at the lake with the view of col (which, I reckon, is the word stem of colluvium).
Colluvium, Col, and Alluvium
Lots of geology here: Arête: the jagged peaks; Cirques: the glacier-filled round areas eroding the mountain; Col: the knife-ridge, mountain pass up top; Colluvium: the rocks and sediment in the foreground, which is a giant landslide.
Sometimes colluvium and alluvium are confused for each other. This is very understandable, as sometimes deposits are really both. But, first: definitions.
- Col: the high mountain pass created by arête erosion.
- Arête: the sharp ridge left over after cirque glaciers erode the surrounding area.
- Cirque: deep, semi-circular basin caused by alpine glacier erosion.
- Colluvium: Soil and rock that has moved downslope due to gravity.
- Alluvium: Soil and rock deposited by flowing water, such as a river.
The thing is, the world is not a simple place, so sometimes both colluvial and alluvial processes act together. You might see a big pile of jagged rocks at the base of a cliff, or boulders on top of some trees that look like they fell from above – that’s straight up colluvium. Or you might see water running through a landslide where the rocks moved on their own, but were started or are continued along by flowing water. There are good examples of both along Cutthroat Lake Trail. But first, a little about the trail itself.
Cutthroat Lake Trail
Gentle slope; great views: Hinkhouse Peak.
Cutthroat Lake Trail is a fairly easy high-mountain hike. It ends at Cutthroat Lake …. or you can continue on Cutthroat Pass Trail (of which the Cutthroat Lake Trail is a part). Cutthroat Pass Trail leads to a series of trails that run along the tops of the mountains (the col). You have to be able to find it, however. … something that we were not able to do, though we had our suspicions (I think you might need to wade across the wetland outlet to the lake on the trail that first reaches the waterbody. There’s a mysterious log that looks like it may have once been a bridge, only it doesn’t really cross the water).
The trail is approximately 4 miles (2 miles gently up hill in and 2 miles gently downhill out the same way).
The Cutthroat Lake Trail can be reached by State Route (SR) 20. I drove there from the east. If you’re coming from Seattle, however; it will be easier to drive along SR 20 from the west. You’ll want to turn north (right from the east, left from the west) onto Forest Service Road 400. Forest Service Road 400 is approximately 1 mile upslope (west) from the Lone Fir Campground. There are signs.
Trail Beginning: Alluvially-transported Colluvium
The large, angular rocks indicate that this alluvium was colluvium recently. In fact, it might not be alluvium at all, but colluvium just sitting in the river. If the rocks are alluvial, they would need to be transported by the stream.
Not far from the Cutthroat Lake Trail head, is Cutthroat Creek. From the bridge, you can see the large, angular rocks within the waterway. The creek drains Cutthroat Lake. However, as you will see along the trail, rocks tumble from the cliffs above. A close-up of the creekbed (below) shows the different sizes of angular rocks. When rocks are in a stream for a while, the water usually rounds them so you get those characteristic pebbles. The visible rocks here look like they haven’t been there that long.
The rocks in Cutthroat Creek are still fairly angular. The water has not yet rounded them very much.
Cutthroat Lake Trail Rockfall
This tree is one of many whose crowns were lopped off by boulders crashing down the mountain.
I would hate to be a tree in these parts. There are tons with lopped-off tops just upslope from boulders. They probably lost their crowns when the boulders bounced too low. Other trees have all sorts of bends and scars, from unstable ground and ecstatic boulders passing through. Colluvium in action: it’s not graceful…..well, sometimes it is, but I doubt the trees would give it any points for style.
- This boulder is one of many that crashed down the mountain and landed in the forest. Note trees for scale: pretty huge.
Cutthroat Lake Trail Landslide: Colluvium with a Little Alluvium Thrown In
The Cutthroat Lake Trail crosses over a large landslide, which has turned it into a stream. This stream alluvially carries sediments within the colluvium.
The photo above is the trail as it crosses an enormous landslide. The landslide took out a lot of trees, providing a fantastic view of Cutthroat Mountain. This was the point from which the photo of the col, arête, cirque, colluvium features within the definitions section was taken. Water rushes down the landslide in a meandering stream. In fact, although this landslide is a colluvial fan (fan-shaped mass of colluvium), it is acting like an alluvial fan (fan-shaped mass of alluvium). This is an area that is both alluvial and colluvial. Fear not! There is a detour.
The detour is less sketchy than it looks, but be careful.
This stream detour crosses the colluvial fan upstream (northish) of the original trail. I missed it going up the Cutthroat Lake Trail, but it is really obvious on the way back. So if you don’t want to get your feet wet and come to the stream, backtrack a few feet and you should see the bypass. However, going both ways get you good views and the glacial water is refreshing. One of the great things about the bypass is that it offers a better view of the colluvial fan. Before you do though, note the rounded nature of the water flowing over the trail rocks. That water diversion has been working a while.
This is a classic colluvial fan with the debris fanning downslope from its source. You can see a bit of the stream (alluvial) in the lower left-hand side of the photo.
This colluvial fan is classic. It fans out from its source to the downslope. This viewpoint from the Cutthroat Lake Trail detour also shows the alluvial components with the glacial stream braiding through the rocks.
Stream Enhanced Colluvium near the Head of Cutthroat Creek
We’ve almost reached Cutthroat Lake. The rocks in the creek are colluvium. However, they’ve been there longer than the rocks at the Cutthroat Creek Trailhead. See photo below for explanation. Note: the log is fastened and stable.
We’re almost there! The lake is over the log, up a little hill, and around a corner. So we’re also near the head of Cutthroat Creek. The rocks here are also colluvium. However, they’ve been at this location longer than the rocks in the Creek near the trailhead. The rocks here are more rounded. They’ve been shaped by the stream longer. Rocks at both locations (and all along the trail) mostly consist of granite, so it’s not a different type situation, just time.
This is a close-up of the stream rocks near Cutthroat Creek’s outlet from Cutthroat Lake. Even the rocks just above the waterline are more rounded than those near the trailhead. The stream has been shaping these for a while.
Boulders guard the wetland entrance to Cutthroat Lake. Cutthroat Peak is the backdrop. Not bad, eh?
We’re here! This is the view as you first arrive at the lake, coming from alongside a wetland/stream. Of course, lots of boulders are everywhere.
As you round the lake (as much as you can – I think Cutthroat Creek is as far as you’ll go around the lake), you see more colluvial features of Cutthroat Peak. Many, including the col (jagged edge of the mountain top), the arête (jagged pinnacle formed by cirque erosion), cirques (the bowls alongside the arêtes and cols filled with glacial snow), and colluvial fans (more fan-shaped rock piles just above the lake on Cutthroat Peak on the opposite side of the lake from where we stand).
In fact, I reckon that Cutthroat Lake itself is a cirque lake (lake formed within a cirque). It certainly has the right circular, bowl shape and is in the correct location. Whichever it is, enjoy your hikes and surroundings!
This photo shows a col (ridgetop), arête (Cutthroat Peak itself), cirques (the bowls holding the glaciers), and colluvial fans (the fan-shaped rock piles surrounding the lake edge).