Kimberley Nature Park
Geology

The following information on the geology of the Nature Park was prepared for us by Bill Olmsted. Bill is a long time resident of the community who taught geology at Selkirk High School and spent a great deal of time outdoors and in the classroom learning about the processes that shaped the land in our region. The following text and drawings outline his interpretation of the events and forces that helped give the Nature Park its unique and interesting topography.

Bedrock Geology

The area underlain by the Kimberley Nature Park is mostly unconsolidated glacial-fluvial material. The little bedrock that is exposed belongs to either the Aldridge formation or the Moyie intrusive. Both formations have been folded and faulted.

About 2 billion years ago the Kimberley area was part of a large, shallow sea. A land mass to the east provided fine material (clay, silt, fine sand) that accumulated off the shore of this sea. Now and then, turbidity currents would move the accumulated sediments out into deeper, calm water where they would settle out in layers. Because the ocean floor was subsiding at the same rate as the sediments were accumulating, the ocean remained shallow but great depths of sediments could collect. Over long periods of time these sediments would become compressed under their own weight, the water squeezed out and the sediments lithified. Geologists have arbitrarily divided these thick rock assemblages into parallel units or formations. Each formation can be recognized in the field by such properties as color, lithology and mineral content.

The first sediments to accumulate in the ancient ocean (and therefore the oldest) have been assigned to the Fort Steele formation. The rusty weathering rocks of the Aldridge were next youngest, followed by the purple and green rocks of the Creston formation. Sometime in the ancient past (1.4 billion years ago) the Aldridge rocks were intruded by igneous rocks (1). These Moyie intrusives were jammed in more or less parallel to the bedding of the Aldridge and formed a series of sills and the occasional dike.

During deposition of sediments that were destined to become the Aldridge formation, the ocean floor developed a series of vents that spewed out hot, mineralized water into the cold ocean water. (Similar vents are being examined these days along the Juan de Fuca Ridge in the eastern Pacific Ocean off Vancouver Island.) These hot vents or "black smokers" produced a shower of minerals such as galena and sphalerite that precipitated onto the ocean floor. Normal sedimentation was also still taking place, so in this way, layers of sediments were deposited on top of the ore minerals and the cycle was repeated many times building up a thick ore body that would become the mighty Sullivan Mine.
Eventually, in response to tectonic forces, the whole area was elevated above the level of the sea. Once this occurred, erosion of the surface could commence. The same forces responsible for elevating the rocks were also responsible for their deformation and faulting. In the region of the Nature Park, erosion has been deep enough to remove the overlying Creston formation, but not deep enough to expose rocks of the Fort Steele formation.

(1) Zartman, R.E., Peterman, Z.E., Obradovich, J.D.. Gallego, M.D. and Bishop,D.T., in press, K-Ar, Rb-Sr and U-Th-Pb ages of the Crossport C sill near Crossport, Idaho: Idaho Bureau of Mines and Geology.
(See Preliminary Map 54, Geology of the Cranbrook Sheet and Sullivan Mine: Trygve Hoy: B.C. Ministry of Energy, Mines and Petroleum Resources for general geology and sections.)

Surficial Geology

The surficial geology in the vicinity of the Kimberley Nature Park is very much the product of glacial outwash deposited alongside ice-margins and superimposed upon bed rock surfaces. The surface we see today has had a complex history. Active glacial ice, stagnating glaciers, deposition and erosion by meltwater streams, the shape of underlying bed rock and bursting ice dams have all had a role to play in this history.

Clues to this history are to be found in glacial erratics, kettles, the location of clay, sand and gravel deposits, the occurrence of glacial striations, the shapes of the hills and mountains, and in the composition, elevation and location of benches and plateaux. Interpreting these clues presents a fascinating, though difficult, challenge. Each trip into the area will add a bit more information to help with the puzzle. To many of us, trying to piece together our local geological history is yet another way to enjoy the out of doors and the Kimberley Nature Park.

Look over Figure 1 below...

This figure shows the maximum extent of glacial ice in the area. Glaciers have advanced and retreated at least four times in the past million or so years. The most recent glacial advance in this area likely began about 25 000 years ago, reaching its maximum extent 14 000 years ago. Ice from alpine areas moved downslope along the valleys and coalesced into a thick glacier occupying the Rocky Mountain Trench, east of the Kimberley Nature Park. Ice in the Trench reached a maximum elevation of about 7 400 feet (approximately 4 900 feet thick) and moved southward into the USA. (1) Only the peaks of some of our taller mountains, such as Fisher Peak, the Steeples, Mt. Buhl, Mt. Lindsay and Bootleg Mountain, remained above the surface of the ice. North Star Hill (the Kimberley ski hill) was completely buried. So, of course, were all the trails within the Nature Park.

Active glaciers affect the landscape in two ways. At the sole of the glacier, rocks imbedded in the ice act like rasps and scour the bedrock over which they move. This action tends to produce smooth, rounded surfaces, often containing scratches or striations. Some of these surfaces can be found within the Park. Alpine glaciers follow the same valleys that streams did before glaciation-except the ice moves in far straighter lines. Because of this, ice scoured off the spurs that descended from the high ridges to the valley bottoms. Geologists call these cut-off ridges "truncated spurs" and they are useful in determining how deep the valley glaciers were. In cross section, glaciated valleys are U-shaped as opposed to the V-shapes of water formed valleys.

The other work done by glaciers is to move loose rock down slope. In a temperate climate such as ours, freeze-thaw cycles result in the breakup of bedrock by frost wedging. The slopes above the glaciers go through numerous freeze-thaw cycles and the loose material wedged out of the bedrock tumbles down on to the glacier or rides down to the glacier on a snow avalanche. Frost action at the sole of the glacier can also remove chunks of rock which then ride about embedded in the glacier. The down slope movement of the glacier will bring this load of loose rock to the valley bottoms. Acting like giant, slow conveyors, valley glaciers move rock debris from the uplands to the lowlands.

Near the top of the T-bar line on the ski hill, just above tower 16, glacial striations (as well as scratches from vehicles) can be seen in the bed rock of the Aldridge formation. These striae show the direction of ice movement at one time when the ski hill was buried in ice. Two large glacial erratics, derived from granite along the upper Skookumchuck River to the north, can be found on the Kimberley Nordic Ski Trails just outside the Park. One is on the Spruce Trail near light standard 45 (upper side) and another is in the trough to the east of the Spruce trail near light standard 41. Other similar erratics have been found on Townsite hill, on Selkirk hill, near Cherry Creek and at Matthew Creek canyon. These erratics indicate that this area has received rock material from areas to the north of us so the ice moved in a southerly direction in the Nature Park.

Truncated spurs, horns, U-shaped valleys, alpine tarns, arrets, cirques, kettles, outwash plains, and polished bed rock are some of the glacial features that can be seen in the nearby valleys of Mark, Matthew, St. Mary and Perry Creeks. The absence of terminal and recessional moraines in the valley bottoms is due to their burial by glacial outwash.

(1) J.J.Clague; Can.J. Earth Sci.,12, 595-605 (1975)

In response to changing climatic conditions the glacial ice began to melt back starting about 12, 000 years ago. As the ice decayed, meltwater could begin to erode the countless pieces of rock that had been buried in the ice or that were riding on its surface. Alpine glaciers were still bringing rock debris down the valleys where torrents of meltwater could move it around, round off the pieces and deposit some of it in quiet places.

Deglaciation involved a thinning of the ice as well as shrinking along the edges. As the ice thinned, some mountains began to emerge from beneath the ice. North Star Hill, Bootleg Mountain and the mountains near Mark Creek Pass (north of Kimberley) would be some of the first to reappear. At one time, the western edge of the ice in the Rocky Mountain Trench was jammed against the exposed sides of Sullivan Hill and North Star Hill near Lois Creek, Trickle Creek Golf Course and Whitetail Valley. Meltwater used this boundary as a stream bed.

As meltwater moved over all that loose, jagged rock carried by the ice, erosive action began to smooth the material and to make it smaller. The longer it was subjected to the action of moving water, the more rounded, smaller and better sorted this material became. Eventually it became the cobbles, gravel and sand (collectively called outwash) that we recognize today. In some places, this outwash rests upon glacial till deposited directly from ice of a previous advance. This older till can be seen below the silt near the Kimberley South Inn.

Where ice lay against the side of North Star Hill, streams flowed along this boundary and deposited outwash in some places. These deposits formed the small benches and plateaux within and around the Park, such as along Centennial Trail, Snowbird, the southern part of Romantic Ridge and the very southern end of Whitetail Valley. So, as the ice stagnated and retreated, huge volumes of outwash were being moved about and deposited by meltwater streams. Ice in the Rocky Mountain Trench retreated eastwards and as it stalled periodically, meltwater channels formed in the outwash along its western margin. Lois, Houle, Mather and Lost Dog Creeks had their starts as ice-margin streams.

As the ice got really rotten, parts of this stagnating ice became separated from the main glacier, forming giant ice blocks. Outwash could be deposited around these ice blocks - but not beneath them. When these giant ice cubes finally melted away, a depression or hollow formed in the outwash plane at those spots. (See figures 3A, 3B and 3C) These depressions, called kettles, can be over a hundred feet deep. Within the Park, most kettles are 30 to 70 feet deep. Kettles can be found in many places within the Park such as: on the golf greens that border the Park, near the Norton Ave. access, between Elbow Road and the highway, near Eimer's Pond, west of Ponderosa Ridge, west of Romantic Ridge, south of Jimmy Russell Rd. just before it meets Army Road, and at the south end of Apache Trail.

Deposition of outwash also took place at some locations where ice lay against the mountain walls. A broad strip of land at about 4100 feet in elevation extending from upper Kimberley Creek through the Nature Park to the St. Mary valley held stagnant ice and ice blocks jammed against the newly exposed bed rock . Outwash can be seen in nearly all locations in the Park. Look for fairly well-rounded cobbles, gravel and sand. This material is not particularly well sorted by size. In some locations, as along the southern parts of Apache Trail, the unconsolidated outwash can be seen as a thin veneer resting on bed rock. In other places the outwash deposits have been entirely removed so that the bed rock is now visible.

There are two types of bed rock that underlie the Park. Rusty weathering, slate-like rocks of the Aldridge formation (argillite and quartzite) have been intruded by igneous rocks belonging to the Moyie formation. The Moyie intrusives are dark colored, crystalline rocks of diorite and gabbro composition. Both rock formations are of great antiquity and pre-date any life forms. These formations are exposed along Apache Trail. In addition, rocks of the Moyie formation can be seen on the cliffs leading up to Dipper Lake and at the Viewpoint near the Shannon Trail-Bear Trail junction. The Viewpoint rocks also show some of the sculpting that occurs when glacial ice grinds over bed rock.

By now the sides of the Rocky Mountain Trench are pretty much ice-free and the local alpine glaciers are in serious retreat up their valleys. The Trench and lower valleys would be choked with outwash from the melt-back of ice and the braided streams would be transporting huge volumes of rock debris and depositing it in any quiet areas. St. Mary River would lack the meanders and sharp bends that characterize it today.

At this time, the large bowl occupied by Whitetail Valley, Four Corners out to Trickle Creek Golf Course, was occupied by a huge, two-tongued ice block that allowed deposition of sediment only along its margins. (See figure 3B) On its eastern side, this deposition would form Ponderosa Ridge and its lower extension near Higgins St. The ice block's other tongue filled the basin west of Romantic Ridge and east of Upper Army Road. Deposition along the margins of this ice would eventually make up the material for these two very narrow ridges. (See figures 3B and 3C) Water from this ice moved northwards through the golf course area and into Mark Creek. Once the ice was gone, local run off sliced the Ponderosa Ridge and developed the watercourse now occupied by Eimer's Creek.

No doubt the depressions now occupied by the Duck Pond and Eimer's Pond were being formed about this time and represent places where deposition of outwash was prevented by ice blocks. A small pond formed against the ice at the south end of Duck Pond Trail, near where it descends to the Apache Trail. Into this pond sand was deposited that provides the soil conditions needed for the Yellow pine that now grow in this area. In the vicinity of Eimer's Pond, late stages of de-glaciation involved stream drainage into Mark Creek valley at Higgin's street. The gated access road from this street occupies a minor run off channel that carried water along Lower Army road, the northern part of Elbow road and Eimer's road. This stream removed enough glacial debris to form part of the eastern side of the very narrow Romantic Ridge.

Near the end of the glacial episode, perhaps 7000 years ago, a blockage formed across the Trench, southeast of Kimberley. (2) This blockage prevented meltwater carried by St. Mary River from escaping. The dam resulted in the formation of a large, but shallow lake into which clay and sand were deposited. This fine clay and sand is a pale yellow color and is very visible along lower St. Mary valley, Marysville, Porteous, Wycliffe, lower Perry Creek and at the curve leading to the overpass at Cranbrook. Sediments carried by Hellroaring Creek were deposited into this same lake forming a small delta at the eastern end of present-day St Mary Lake. This delta would later form a barrier that impounds today's lake.

Only tiny remnants of the alpine glaciers are shown in figure 4. These bits of ice occupy bowl-shaped basins called cirques by geologists. The lakes that frequently collect in these cirques are tarns. Many tarns are still present in the Mark Creek Pass area.

Eventually, whatever blockage formed the glacial lake broke and the sudden release of all that water caused rapid down-cutting along the lower parts of the St Mary River. Much of the clay and sand that had accumulated in the bottom of the lake was washed down-stream. Down-cutting by the river produced terraces in the outwash and in the older glacial till beneath it. This left the St. Mary River well below the general level of the outwash plain and bordered by cliffs of outwash capped by sand and clay. At places these clay-capped gravel cliffs form the familiar "hoodoos" of today. Figure 5 shows (in yellow) where some of the clay-topped outwash and till can be found. Within the Nature Park these features can be seen from Sunflower Hill and the Viewpoint at the top of Bear Trail.

From a geological point of view, a person walking in the Nature Park will see mostly glacial deposits that have shared a similar history and that differ only in detail. Kettles, kame, terraces and outwash channels are the most frequently encountered features. A few places in the Park will enable one to observe the two types of bedrock present. We have seen that present day Kimberley, Houle, Lois and Mark creeks are remnants of much larger streams that once carried icy meltwater to St. Mary River. One such stream also occupied the ravine that runs from Meadowbrook, through the sawmill, under the tram way, through the city works yard and into Mark Creek in the vicinity of Black Bear bridge. Selkirk School occupies a site that is bordered by two outwash channels. These channels are far larger than is required to carry away present-day loads of rain and snow melt. But hey, maybe they will yet be needed to carry away the next glacial run off. Who's to say?

(2) J.J.Clague Can. J. Earth Sci.,12, 595-605 (1975)

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