Gallagher's Canyon Field Trip

Dr. Murray A. Roed

Approximately 50 million years ago, volcanoes erupted in the Kelowna area and along the Okanagan Valley. One example of this volcanic activity is Layer Cake Hill in Gallagher's Canyon(see sketch at end). Since that time, the land has undergone many changes. Erosion by large streams removed much of the volcanic bedrock, carving a broad deep valley along where Mission Creek now flows. Then the Ice Age occurred and the land was eroded and carved by several glaciers during different times in the last one to two million years.

The last glacier is called the Fraser Glaciation. It started to advance about 25,000 years ago and overtopped all of the mountains of the Okanagan. It began to melt away about 15,000 years ago and finally¹ disappeared about 10,000 years ago.

As the Fraser Glacier melted in the Mission Creek Valley, the valley was blocked or dammed for some time by large blocks of stagnant ice and debris in the glacier at Gallagher's Canyon. Material deposited from the ice served to partly infill the ancient valley. But lots of ice remained and the ice was still melting. That produced a lot of meltwater. The water could not escape because of the ice dam in the canyon. Therefore, a large lake (a glacial lake) was formed along the upstream part of Mission Creek Valley. The flat topped terraces along the present valley sides represent the bottom of this ancient lake. Examples of the silt deposits in this lake can be seen on the field trip.

So much water built up in the glacial lake behind the ice dam that finally the dam burst one day, and a catastrophic flood occurred. All of this rushing and turbulent water was responsible for cutting a steep-sided gorge along the face of Layer Cake Hill and eroding what we now call Gallagher's Canyon. One side (the north side) of this gorge was the steep face of Layer Cake Hill…since there is not a matching rock wall on the other side (the south side) that space must have been all glacier ice and debris, and the ice has since melted.

During this catastrophic erosion event perhaps about 10,000 to12, 000 years ago, a lot of meltwater was also coming from KLO Creek valley. The combination of these glacier flood waters with that of the outpouring of the glacial lake along Mission Creek valley must have created a huge whirlpool that swirled around carving out a portion of Layer Cake Hill and finally forming a pinnacle of rock that we call the "Pinnacle" today.

This flood also carved into glacial deposits downstream of the Canyon creating terraces in the vicinity of Hollywood Road, and all material was swept into the main Okanagan valley at Rutland forming the Rutland Fan. Most of Rutland is built on the very large fan deposited at this time.

Since the end of glacial time, Mission Creek has continued to erode deeper. There have been numerous climatic changes. Geologists suspect seven or eight global warming and global cooling intervals in the last 10,000 years. At times rainfall was perhaps ten times what it is now, and during other times there was even less yearly precipitation than the present 55 centimetres. The climatic fluctuations have served to erode the present stream valley and deepen it perhaps another 3 to 5 meters.

Points of Interest

1. From the rim of the valley:
Notice the flat-topped grass covered terraces across the valley. These represent the bottom of a glacial lake. The bottom of the glacial lake stretched over the whole valley about 10,000 years ago. Since then erosion by Mission Creek and other creeks has removed most of the silt from this lake bed. The terraces that can be seen are remnants of this former landform.

2. Along the road into the valley:
Material deposited in the glacial lake can be seen. The material consists mainly of silt and some sand in beds or bands that can be observed. There are some gravel lenses in the silt beds; these gravel lenses represent deposits from fast-flowing glacial streams that entered the lake and existed for a very short time.

3. Down the path into the valley:
More and more boulders can be seen along the path deeper in the valley. Most of the boulders are glacial erratics. They were plucked out of bedrock by glaciers and carried to this position. When the ice melted the boulders and other finer sized material that was in the ice formed a deposit known as till.

The glacial lake silt and glacial till are not consolidated material, so they are known as surficial deposits.

4. Sandstone Outcrop:
Near the bottom of the valley on the right hand side of the path is layered outcrop of pale yellowish gray sandstone and siltstone (a sedimentary rock). This formation is part of the bedrock in the valley. It is called the White Lake Formation. A very large river formed it after volcanic activity had come to an end and long before the glaciers arrived. Looking closely at the rock it can be seen to contain numerous plant fragments; these are fossils. By studying these fossils geologists and paleontologists can determine what kind of vegetation existed in the area 50 million years ago or so.

5. Near the end of the trail piles of angular rock boulders begin to appear at the base of Layer Cake. These pieces of rock have fallen off the steep cliff and accumulated in piles at the base of the cliff. The deposit is called talus. These rocks have been broken off mainly as a result of frost action. If water gets into the cracks in the rock cliff and freezes, this causes the rock to pop off the cliff due to expansion of the ice. Little by little the cliff is being eroded away. Close examination of the rock fragments may reveal crystals of feldspar that were formed when the molten rock cooled as it reached the surface.

6. Big Rock at Picnic Site:
Using the information given in the field trip, students are asked to write a short essay on "The Origin of Big Rock, Mission Creek". This rock sits in the middle of the creek at the picnic site. It is approximately 8 meters long, six meters wide and about 4 meters high. It weighs about 600,000 kilograms, or 300 tonnes.

7. Gold in Mission Creek:
If the water is not too high and too swift, students will be able to watch how a prospector pans for gold. From about 1859 to 1895 gold was regularly mined by placer miners in Gallaghers Canyon. Some miners took home about 2 ounces of gold every day, and it was coarse, bright and shiny.

8. Trek to the Pinnacle:
This is an awesome trek to get up real close to the Pinnacle, one of the most unique landforms in the Okanagan. An Eagle has made its home right at the top, and can often be seen circling above.

9. The Layering of Layer Cake Hill:
Although the layers of Layer Cake Hill look like a series of lava flows (volcanic rock ), each layer representing a separate flow, modern science has proven this wrong. Scientists now believe that the layering occurred in possible only one thick volcanic flow due to a peculiar way the rock shrinks as it cools. This type of layered structure has been compared to a similar formation in New Zealand where scientists have thoroughly studied it.

10. Mission Creek Fault:
Along almost its entire length Mission Creek valley roughly coincides with another geological feature. When the Rocky Mountains were rising 30 to 40 million years ago, the Okanagan was also affected. A break occurred along Mission Creek; the rocks on the south side rose up perhaps many hundreds of meters; the north side moved down but also moved horizontally perhaps five to ten kilometres relative to the south side. Movement of this amount between rocks is called a fault. The movement along the Mission Creek fault is responsible for creating the great bend in Okanagan Lake.

Geologists know that there is a major fault along Mission Creek because the rocks on the south side are completely different than the rocks on the north side. Rocks to the south are metamorphic rocks that are two billion years old. Rocks on the north side are volcanic (an igneous rock) that are 50,000 million years old. Therefore, there has to have been a lot of shifting of the bedrock to bring these two types of rock in contact with each other.

SKETCH OF GEOLOGIC FEATURES, GALLAGHERS CANYON FIELD TRIP
View is towards the West. Drawing not to scale.

1. This field trip was designed for primary grade students at Black Mountain Elementary School in Kelowna. The trip traverses Private Property, so permission is required from Landowners.