Model Geoscape "McIntyre Bluff, South Okanagan"

McIntyre Bluff, South Okanagan
Acrylic, canvas, 20 X 30", 2000
Price: $750.00

McIntyre Bluff is situated on the western side of Okanagan Valley, halfway between Oliver and Okanagan Falls. Vaseux Lake, part of the Okanagan River system, nearly abuts this prominent landmark but is not shown in this depiction.

The bluff exposes a 500 meter high wall of granitic gneiss, shot through with thin layers of quartz and other mineral veins. The rock is known as the Vaseux Formation and probably belongs to the Shuswap Metamorphic Complex of Precambrian age. This cliff is the steepest and most dramatic in the Okanagan Valley, and the valley itself is the narrowest and most constricted in the Okanagan at this spot. Other geologic dramas have been identified at this site. The rocks have been subject to major tectonic (mountain building) events that have served to fold the rocks into great overturned fold structures at least 10 kilometers wide. The main structure is called the McIntyre Bluff Fold. It is a huge recumbent to isoclinal syncline with a northeasterly trending fold axis. It is also referred to as a nappe. Although three periods of mountain building and folding are recognized by geologists John V. Ross and James S. Christie of the University of British Columbia, the main fold structure dates to at least Permian time, over 270 million years ago.

How was this landform carved out of this mountainous terrain? According to Dr. Hugh Nasmith, who studied the glacial history of the valley in the early 1960's, deep intensive erosion of the Okanagan was first accomplished by one or more rapidly flowing valley glaciers. It is very likely that several periods of valley glacier erosion operated to repeatedly gouge out a path down the valley during the last one or two million years. It is known from other parts of the valley that the bedrock floor has been eroded so deeply that today it is far below sea level at an elevation of -640 meters (-2100 feet) below Okanagan Lake, for example. Overall, in fact, the Okanagan Valley has witnessed the removal of nearly three kilometers of its rock by glaciers, which is almost twice as deep as that eroded from Arizona's Grand Canyon!

Some geologists suspect large ice-sheets that completely overtopped the mountains in this region could have similarly eroded valleys such as the Okanagan. There were several of these ice-sheets that enveloped the Okanagan, and likely all were in excess of three kilometers thick. Consider the extreme power at the base of such a glacier along pre-existing valleys where forces would be concentrated. Some combination of these processes in any event managed to slice through at least 500 meters of the hard metamorphic rocks at McIntyre Bluff, like a knife through cheese! Awesome!

A strange geologic conundrum shrouds McIntyre Bluff. Despite being deeply incised, the rocks at high elevation on McIntyre Bluff record ice flow indicators of a really old ice sheet that flowed southeasterly towards the United States. These ice-flow indicators have been truncated by the more recent gouging out of the bluff, leaving geologists with additional mysteries of the wonders of Mother Nature.