Princeton-Oliver-Penticton Geotour

Okanagan  Geology

The Okanagan Valley is located in the interior of BC and is about 200 km long and 20 km wide. Okanagan bedrock geology is primarily comprised of basaltic lava flows, intrusive granites, carbonaceous sedimentary beds, and foliated gneiss. Most of the surface features were formed by erosion and deposition resulted by glaciation. Large gravel, sand and silt deposits were left by glacial activity during the Pleistocene epoch which was between 11,000 and 9,000 years ago. Features such as deltas and alluvial fans were formed by sediments that were eroded by water and wind after they were deposited by the glaciers.

The White Lake Formation

The clastic sedimentary rocks in the south Okanagan are part of the White Lake Formation. The grain sizes here range from clay size particles to boulders. A paleo-river system was active 55-34 million years ago and deposited the sedimentary rocks seen today. Volcanic rocks integrated in some conglomerates are found in some areas and imply that the sedimentary rocks are younger.

The Okanagan Valley has both plutonic and extrusive igneous rocks. The extrusive rocks are part of Marama Formation and are usually felsic such as Dacite. 55 to 34 million years ago during the Eocene period, there was volcanic activity in the Okanagan. These formed mountains seen today including Giant’s Head, Knox Mountain, Mount Boucherie and Munson Mountain. Plutonic rocks in this area are normally granite or granodiorite and are associated with the Okanagan Valley Fault. In some locations, these rocks are metamorphosed. Skaha Bluffs and Trout Creek Canyon are good examples of these.

The rocks in the east side Okanagan Valley are composed of metamorphic and plutonic rocks. In the north, the rocks are primarily composed of the Monashee Gneiss which is over 2 billion years old. In the south side, Okanagan Metamorphic Complex rocks are dominant. These rocks are mylonitic gneiss.