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There are three main groups of bedrock in the area: the Monashee group, the Mount Ida group and the Kamloops group. These groups range in age from Precambrian to Quaternary and in composition from high grade metamorphic to poorly compiled shales.

The oldest rock in this area is the Monashee group. There has been controversy about the age of these rocks, but recent work favours a Proterozoic to Lower Paleozoic age. This group consists mainly of quartzite, hornblende, marble, and limestone. Quartzite, a metamorphic rock, is usually white, gray, pink or buff in color, and is a massive, hard and often glassy rock. Heat and pressure from the earth transforms quartz grains in sandstone to quartzite. Hornblende is any of a group of fairly hard rock-forming minerals. They occur in many igneous and metamorphic rocks. Hornblendes range in color from dark green to dark brown or black. Most hornblendes occur as shiny crystals shaped like a prism but some are small, irregular shaped grains. All hornblendes contain aluminum, calcium, iron, magnesium, silicone and oxygen. Many also contain potassium, sodium, and titanium. Marble is a metamorphic rock. It was formed by calcite in limestone which recrystallized to form marble. Marble is many colors, usually mixed, and has medium to course crystals which may be banded. Limestone is a sedimentary rock which is white, gray, and buff to black and red in color. It is dense and forms thick beds and cliffs which may contain fossils. Sedimentary rock consists of layered materials which harden into solid rock. The Monashee group is most evident around Ashton Creek and along Hunters Range.

The second oldest bedrock is the Mount Ida group. Thought to be formed within the Paleozoic age, these rocks are found around Gardom Lake, Mara and Larch Hills. It consists of flaggy limestone, slate and hornblende gneiss. Slate is a metamorphic rock formed by soft shales and clays hardened by the effects of heat and pressure. It is usually black, red, green or purple in color and is fine grained, dense and splits into thin, smooth slabs. Gneiss is also a metamorphic rock, a medium to course-grained rock arranged in bands and gray and pink to black and red in color.

The youngest bedrock in the area is the Kamloops group. It was formed in the early to middle Tertiary age and makes up the Enderby Cliffs. There is evidence this bedrock once covered the area between Cache Creek and Mable Lake, but has slowly eroded away. This bedrock consists of coal, basalt, sandstone and shale. Basalt - an igneous rock formed when the magma from volcanos cools - is dark, usually greenish-gray to black in color and has dense, microscopic crystals that often form columns. Coal, a sedimentary rock, is shiny to dull black and is brittle, found in seams or layers. Sandstone, also a sedimentary rock, is white, gray, yellow or red in color with fine or coarse grains cemented together in beds. Shale, another sedimentary rock, has dense, fine particles. Shale is soft, splits easily and the smell resembles that of clay. Shale is usually yellow, red, gray, green or black in color.

Kevin Early, Myrna Hannebauer, Dusten Tulak
ALF School 1989