At the end of the last Ice Age a dam of ice blocked the flow of the Thompson River and Glacial Lake Thompson was formed.   Sediments were carried by steams and rivers into the lake valley and built up over a long period of time.   The floor of this glacial lake was higher than the current river valley bottom.   The terrace benches on both sides of the river east of town was the lakebed floor.  As the ice melted, the lake was drained and the South Thompson River began to flow west again, eroding a channel below the terraces.

As we drive east from Kamloops we can see the silt cliffs on either side.   Seasonal creeks and streams have cut gullies between the silt cliffs, some of which can be used as exploration routes to see the more interesting erosion features.

Some of the most accessible parts of the silt cliffs are found on the south side of the river, using Valleyview Nature Park, Lower Rose Hill Trails, or Dallas-Barnharvale Park.   The north side of the river has fewer access points and some private lands.   Nevertheless, with a bit of exploration, we can find routes in the erosion gullies up to some impressive silt cliffs and erosion features.

Since the retreat of Glacial Lake Thompson, river erosion of the soft silts has scoured out the river valley of the South Thompson River.   On the sides, gullies have been eroded by meltwaters from the hills.   When two parallel gullies erode a short distance away, a point is created, the top of which is the terrace formed by the lake’s silty floor.

Go up any of the gullies and we can see the layers of silt from where we are standing up to the terrace bench.

The day I scrambled up this gully, erosion was clearly in progress as the melting snow caused muddy slumps down toward the lowest point of the seasonal creek valley.

The sloping sides covered in grasses and sagebrush are just silt layers that have slumped over thousands of years.

Castellated structures are formed by the effects of creeks scouring deepening gullies to each side, but also seasonal erosion by snowmelt, rain, and wind.

Occasionally silt-clay pillars can be found on the silt cliff ridges.

Exploration of these erosion gullies can be a challenge.   It is much easier to find a route to up to the terrace bench in dry conditions.   If you want to see the silt cliffs, start with the trailhead near Valleyview Arena.   There are many days of further exploration on the terrace benches, where you can find terrace spines, ridges, bridges, sinkholes, grasslands, sagebrush slopes, and erosion features.

While struggling up an erosion gully, I was being carefully observed…