Experience Westbank: Geology

Ancient Hills of the Okanagan

by Deborah Greaves (April 2006)

Not everyone realises it, but many of us who explore this valley for any length of time tend to fall inexplicably in love with its terrain.

The land doesn’t always grab people at first.

After many years under the Big Sky of the prairies, half a lifetime on the emerald slopes of Vancouver Island, or a childhood surrounded by the sharp peaks of the Rockies, some people are bewildered at the way the Okanagan Valley’s understated landscape can have such magnetism. On some of us, this semi-arid area, pastel-hued in the rain-shadow of the Coast Mountains, has a subtle but relentless pull.

Many rave about the lake - that long and impressive body of blue that courses from one end of the valley to the other. In my opinion, though, it’s not the lake that solicits human devotion. Experience Westbank has learned - just as I’d often suspected - that Lake Okanagan was never the main show.

Explosive Past

At one point in the evolution of this region, after the valley was ravaged by explosive volcanoes, when all was raw and heaving and plant life was new, a mighty and astounding river roared north up the valley - so gigantic and fast that it swept huge boulders along as though they were minnows.

Big Water

The massive river that roared through the Okanagan Valley over 60 million years ago, Dr. Murray Roed, local Geologist, tells us, is represented today by the White Lake Formation that outcrops extensively in the Westbank area. The Formation is a collection of rocky debris, petrified sand, boulders and silt as well as compressed plants, and it’s no less than 3,000 feet thick. This formation was created in the Okanagan Valley over 30 million years before the Rocky Mountains - one of BC’s youngest mountain ranges – reared up from the earth.

Glacial Lake

As recently as 11,000 years ago or so, the valley had a dam at one end made of stagnant ice near Vaseux Lake, and a huge glacial lake known as Glacial Lake Penticton was created. At its maximum extent, Glacial Lake Penticton extended from Okanagan Falls in the south to beyond Enderby in the north. The giant lake encompassed the entire chain of what are now separate valley lakes: Skaha, Okanagan, Wood, Kalamalka and Swan lakes. Much of the Lakeview area, Green Bay, Sunnyside, Gellatly Bay and Westbank were all completely submerged - as well as most of Kelowna.

Perhaps 10,000 years ago, glacier ice had largely disappeared, but the level of Glacial Lake Penticton was still high above the level of current Okanagan Lake. When the ice dam finally broke, a catastrophic flood dug deeply into the glacial lake basin, creating picturesque silt bluffs that now grace the famous Okanagan landscape.

Then There was the “Carving”

If not for the carving done by repeated glaciations, Okanagan Lake would not exist. Lake Okanagan began partly as a deep rift in the earth over 60 million years ago, then became a valley of volcanoes. After that, it was the site of the gigantic river system that created the White Lake Formation, and finally a valley, deeply eroded by perhaps four different glaciations. At the end of the last glaciation, Glacial Lake Penticton formed as the Fraser Glacier melted.

‘Kettles’ Aren’t Always on the Stove

A stagnant body of buried ice was all that remained of the Fraser Glacier when much of Glacial Lake Penticton drained away. When the remnant body of ice itself melted, it left a “kettle lake” - a lake that is created when water fills a depression left by melted glacial ice. This newest water body is the lake we know and love today, Lake Okanagan.

Oldest Rocks in BC

Today, visible from all over the Westside, seamed, undulating and compelling, some of the oldest mountains and rocks in Western Canada still remain. One of the areas these can be seen is Okanagan Mountain Park. Here are ancient mountains, about two billion years old - bisected in many places by younger mountains and rock that pushed up from below - and still scorched in places from the intense forest fire of Summer 2003, that you see when you gaze across the lake - particularly from Westbank, Peachland, and Summerland.

New Roads, Ancient Secrets

In recent times, the legacies of the Great River of the White Lake Formation, the Fraser and other glaciers, and Glacial Lake Penticton can be seen in an increasing number of places on the Westside. Wherever bulldozers and dynamite have stripped away the recent layers of soil, trees and history, stories that were inscribed centuries ago into the land are there for us to read.

Many of the excavations for new roads, stores and neighbourhoods on the Westside are opening windows into the past. When a new rock face emerges in the wake of road or building construction, the bared rock shows fault lines of the activity that forced the earth to move, as well as imprints of leaves and fish and multiple layers that tell of the many changes in the surroundings. If you examine a rock and see lines of soft charcoal within it, you can see and touch evidence of a long-ago world.

The Experience Westbank Geological Tour

Experience Westbank went on an exploratory tour recently with artist and author Murray Roed, who explained some of the geological marvels of the Westside.

“With all the construction that’s gone on here recently,” Dr. Roed told us in April, “someone should be documenting the findings (revealed when the hills are opened) - and with the right interpretive signs, the Westside could be doing a busy geological tourism business.”

Dr. Roed’s List of Marvels

Mount Boucherie: One of the most important and prominent geological landmarks in the Okanagan Valley, this distinctive mountain is nevertheless just a small remnant of what this “explosive” volcano once was.

The Mt Boucherie that Westsiders live with is a fraction of the size of the original volcano, but Dr. Roed says it is nevertheless “Fantastic, for the geological insights it offers.”

Mount Boucherie’s original and violent eruptions had long ceased, when forces reawakened from deep below, and new eruptions blasted up through the mountain with fresh energy.

Also, this extinct volcano once had giant Glacial Lake Penticton lapping against its sides. The lower slopes on this mountain have many interesting features, and one is the lateral moraine that encircles the mountain on the north, east and west sides.

Another feature, as illustrated on the kiosk at Eain Lamont Park, is the columnar structures in the mountain. When new eruptions forced through the old volcano, lava pushed through “pipes” in the rock. When these new eruptions ceased, then cooled, columns of dacite, similar to basalt, were left in place in the mountain.

As Mount Boucherie aged and eroded, some of these columns were exposed in steep cliffs. As softer rock eroded away from around them, some of the columns tumbled over and onto the ground. They rest there today, a sharp contrast to their surroundings, resembling fallen knights or ancient ruins scattered on the forested slopes.
Stony Bluffs Near Mission Hill Winery: There are several areas within view of the Lake Okanagan shore that are made of either clay or conglomerate sandstone from the White Lake Formation. Here a striking cliff just off Boucherie Road, beneath Mission Hill Winery, exposes conglomerate riddled with interesting holes that make it even more dramatic, especially in the morning sunshine.
Clay Hills and Bluffs Near Gellatly Bay: If you’ve ever walked the grassy pathways of Westbank Community Park just downhill from Johnson Bentley Memorial Aquatic Centre on a wet day, you will have encountered the thick, slippery clay that the entire hillside is made of.

The greasiness and viscosity of that clay makes sense when Dr. Roed explains that it’s the exact same goo that once filled the lake bottom - the bottom of mighty Glacial Lake Penticton. This park - and all of the lower slopes leading to Gellatly Bay - was once underwater.
The Many Calling Cards Left by the “White Lake Formation” The entire Okanagan Valley was once the scene of a mind-boggling geological event that stands out among several major geological events - the dramatic creation of the White Lake Formation. Evidence of the colossal river that once roared through the valley roughly 60 million years ago is everywhere. If you stand on a high ridge, you can spot many of them. See an odd ridge, made of compressed sand or rock, pressed against the lower slopes of a mountain?

Near Gorman Brothers Lumber Products Every day, thousands of vehicles drive by a series of cliffs exposed by the Highway 97 and Glenrosa Exchange road beds that offer vivid pictures of past events. Dating back more than thirty million years before the Rocky Mountains were formed, this area was the scene of one dramatic event after another.

Each layer in the rock of the White Lake Formation here depicts a different geological experience in the valley. Many of the rocks have streaks of charcoal in them, as well as fossils of plants and fish. Some of the layers, made almost entirely of coal, represent the very first vegetation that grew in the valley.
At the Foot of Shannon Ridge Drive off Shannon Lake Road: Another of Dr Roed’s favourites, the ‘fantastic geological feature’ of this rock face is a set of ‘pipes’ that reveal the path of a series of eruptions that forced material up though the hillside, then remained set in the older stone. With your back to Shannon Woods subdivision, stand a few metres away from the base of this rock face and adjust your eyes. Once you see them, you’ll wonder how you missed them before - several ‘pipes’, reaching toward the sky like the branches of trees.

This too, says Dr. Roed, deserves a bronze plaque.

Westside Rocks - Volcanic Pipes

Whether people notice them or not, some prize geological sites are located here. Multimillion-year-old dramatic tales, etched in stone right before our eyes and underneath our feet - more reasons Westbank and the Okanagan Valley are special.

Experience Westbank!