On th Rocks
June 2007

Valleys Exalted, Hills Made Low
by Leopold Hayden Powell

Every valley shall be exalted, and every mountain and hill made low:
and the crooked shall be made straight and the rough places plain.
Isaiah 40:4, att, Isaiah of Jerusalem, ca. 540 B.C.E.

Turn this prophesy of elemental change around in time to read the first statement of the principles of geology. Step beyond human life spans to encounter a different world. An earthquake may suddenly bring the mountain and hill low. The rough places have been made plain over epochs of weathering. Regardless of the rate, change is not only inevitable: it is continuous. There is no point, in time or space, where the rules change. Sea floor was pushed up into mountains by a small set of mechanisms. Rivers always cut off their meanders by the same sort of erosion. We may travel in time, geologically, by paddling down the Kootenay River, from Canal Flats to Wardner. The East Kootenays are a different geological province from the West. Their histories -- deep, old, recent and future -- are linked.

Extending from northernmost British Columbia to near Deer Lodge, Montana, the Rocky Mountain Trench is a magnificent structure. The Purcell-Belt Super Group is just as grand -- an ocean basin, covering thousands of square kilometers and accumulating more than fourteen kilometers thickness of sediment. Both receive a fine discussion in The Roadside Geology of Southern British Columbia. We get great views of both the fault valley and ancient rocks, as we paddle down the Kootenay. If we were paddling on the ancient sea, mountains would have been out of sight, to the west and south, and a vast plain stretching to the east. The hot springs on the sea floor may have supported colonies of bacteria and archea, as well as, depositing the Sullivan Mine ore. Common wisdom holds that the land was barren of life; however, stromatolites would show at low tide. With cyanobacteria forming stromatolites, it is interesting speculation that they may have cohabited with other life forms, in crusts, similar to modern lichens.

A few remnants of younger rocks lie near the river. The pre-Cambrian plain was lowered by erosion. The continent sank, as it aged and cooled. For a half billion years, it was covered by a shallow sea. Thin layers of fine sediment covered the sea floor evincing mountains far to the east and north. Traces of that mud and lime carried on to the present West Kootenays. One of the world's most revealing sets of fossils was buried in a pocket of that sea. In August, we will be hiking to Mount Wapta and the Burgess Shale in Yoho National Park. Plan ahead for that trip. To visit Burgess Shale localities, you must reserve space on an escorted hike. For information on the guided hikes, contact The Yoho-Burgess Shale Foundation at their website (www.burgess-shale.bc.ca/) or by mail (Box 148, Field, BC V0A 1G0), or by email (burgshal@rockies.net). The reservations fill early.

How the Rocky Mountain Trench became such a thoroughfare, the source of the Columbia and Fraser, and the route of the Kootenay is a long time story. Mathews and Monger mention that the youngest rocks, cut by the fault, are five million yeas old. In Montana, granite intrusions bear evidence of movement by the fault, while still molten. That was ninety million years ago. Movement has been west-up, west to the north and west block down, over that long time span.

The Trench remained full of glacial ice, through the time of the great outburst floods. Melt water of the Trench glacier was partly responsible for the repeated and rapid refilling of Lake Missoula, with both water and sediment. The asthenosphere, below crust and upper mantle, is plastic -- capable of flowing very slowly.

Accumulated weight of glacial ice, the huge lake, and sediment depressed the crust, as the plastic rock flowed out, to lower pressure. Nearly one hundred meters depression of that fore deep allowed the Trench to drain, out the courses of the Moyie, Yaak and modern Kootenay River. Fort Steele sits on one of the many terraces, which were created during times of different drainage routes. Skookumchuck and Cranbrook are sites on other terraces. The continued rebound of the land (a few millimeters per decade) helped form the many blind channels and bulrush wetlands. Slow change builds habitats for a cornucopia of plants, abundance of animals, and homes for generations of peoples.

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