If they could talk, what a story boulders could tell

I was at Post Falls High School the other day and I noticed a collection of trash can-sized white boulders that are a prominent part of the landscaping. I wonder how many realize the significance and appropriateness of having those stones gathered together there.

The boulders aren’t a part of the natural geology of this area. They are, in fact, granite, probably originally from somewhere in British Columbia. But they were not brought here, to Kootenai County, by the work of any human hand. They arrived through the forces of nature many thousands of years ago.

They are common enough that one might assume they belong here. I have seen many such stones, from the size of a golf ball to much larger than the high school boulders, all over the lower altitudes of Kootenai County.

They are beautiful compared with the native rock. That’s the gray, crumbly stuff you see exposed at areas around the lake where wave action has uncovered it, or in the road cuts that expose the insides of hills and mountains. It’s basalt.

It cracks easily and crumbles where exposed. It isn’t much to look at, except when seen in the fractured columns that characterize cliffs of basalt. These columns have become a favored part of North Idaho and Spokane International Airport landscaping.

I’m not a geologist, but if I hadn’t become hooked on biology first, I sure could have been. The stories that rocks can tell are fascinating, but you have to speak their language. Since I don’t, I read the accounts written by those who can.

Most recently I have read “Glacial Lake Missoula and it’s Humongous Floods,” written by David Alt and published in 2001 by Mountain Press Publishing Co. and “The Restless Northwest: A Geological Story,” written by Hill Williams and published in 2002 by Washington State University Press.

In earlier articles I summarized how gigantic Glacial Lake Missoula formed over northwestern Montana during the peak of the last ice age, about 15,000 years ago. At the same time, Kootenai and Spokane counties were inundated by Glacial Lake Columbia from the west. Both lakes were created by glaciers that crept over the Canadian border from British Columbia.

The lakes formed from rivers dammed and backed up by the glaciers and from glacial meltwater. Since ice is buoyant, the ends of the glaciers would eventually rise as the lakes got deeper. This tendency to float acted against the weight of the main glacier, and huge chunks of ice – icebergs – would break off and drift on the lake.

Glaciers are moving things. As snow and ice accumulated over thousands of years, and the bulk and weight of the glaciers grew, they came to flow with gravity the same way a river does, just a whole lot more slowly. Needless to say, there was not much that could detour such a moving mass. Thus glaciers would collect whatever was in their path, including rocks of all sizes and shapes, and carry them along.

As the glaciers crawled along, most rocks were pulverized into dust. The survivors were, at the least, rounded into smooth shapes and then held captive within an icy matrix. When the glaciers finally melted, they left behind huge piles of this rubble, called moraines. Icebergs, however, carried their cargo of foreign debris, in many cases, far from the site of the actual glacier.

Especially in the catastrophic floods of Glacial Lake Missoula – there were dozens – and in the period of constant flooding from glacial melting that marked the end of the ice age, hordes of icebergs moved away from their site of origin. Some traveled as far as Oregon’s Willamette Valley, and many landed along the way, including those in Kootenai County.

Wherever they came to rest and eventually melted, these icy barges deposited their rich array of Canadian souvenirs. Wherever they grounded a hodgepodge of rocks lay scattered within a relatively small area. Such a site outside Portland contained a 15 ton meteorite thought to have been float-transported from British Columbia.

And so the Rathdrum Prairie, upon which Post Falls High School was built, is the very threshold of the great Glacial Lake Missoula floods – the catastrophic events that shaped the landscape of the Pacific Northwest from here to the Columbia Basin, to the Columbia River Gorge, to the southern end of Oregon’s Willamette Valley, and all the way into the Pacific Ocean.

Those white granite boulders of British Columbia bedrock that ring Post Falls High School are the small but distinctive reminders that were left to us of the very different, and relatively recent, past that North Idaho has experienced. Those rocks are the remnants of icebergs that were spawned not that far away and were brought here by some of the most profound violence that nature has produced in the last 20,000 or so years anywhere on earth.

Knowing that makes them a whole lot more than simple objects of landscape design. Just think of the stories they can tell, if only we learn how to listen.