In the San Juan Islands bedrock is not far from the surface. Sometimes it is the surface! About 11,000 years ago the last Ice Age scraped its way across the islands in a Northwest to Southeast direction with an ice sheet over a mile thick. Usually that factoid goes in my brain, rattles around looking for a reference point to attach to, then falls to the basement as implausible. I’ve seen ice on the island ponds up to six inches thick, but over a mile? Come on!!
All it takes is time. Our lifespans don’t give us the cognitive reference to absorb the length of time and natural forces that accrue to give us what we see in this photo.
This is bedrock where all the topsoil and sediment has been stripped away, in this case by that thick sheet of ice which had boulders, rocks, pebbles and sand glued by the immense pressure of that heavy ice pushing on them. As the ice accumulated from snow storms over centuries, it was forced to move by gravity, ablation, and complex flow dynamics. This motion caused the aggregate at the base of the ice to grind on the bedrock, and here you can see the larger grooves produced by individual boulders, the visible forensic evidence of unimaginable forces that took place right here.
Notice how the rock appears sanded smooth as if by a craftsman, in this case Mother Nature. In the foreground are tiny striations made by pebbles in the ice, still visible after many thousands of years. In fact the weight of the ice was enough to cause the mountains that were the San Juan Islands to sink into the earth’s mantle, so where I’m living is the ground down top of an ancient mountain.
Thank you for allowing me to don my professorial mortar-board hat and expound on scientific matters. I am obviously engrossed in such trivia, especially when the evidence is right outside my front door!
Another excellent public area for viewing these grooves in the bedrock is the Cattle Point Interpretive Center just beyond the lighthouse at the south end of San Juan Island. However, be advised; parking in the parking lot requires a fee or a ‘Discover Pass’ ($30 annual; $10 one day fee. Apply at State Parks, online, by phone, or when you renew your car tabs.) I stopped there on January 1st and didn’t stay because I had no Discover Pass and hate getting tickets, or arguing with authorities. I am going to purchase one when I renew my truck tabs next month, for there are numerous DNR and State Park destinations even just in my home county that I intend to visit this year.
Photo location: Inside town limits of Friday Harbor on San Juan Island