Observations of Washington State Landscapes, Geology, Geography, Ecology, History and Land Use
Tuesday, March 30, 2010
A Piece of the British Columbia Coast Range via the Juan de Fuca Lobe
I came across this small boulder in the sand of Shishi Beach on the west coast of the Olympic Peninsula. My purpose that day was to reach some unusual bedrock outcrops, but this rock got my attention as I used the beach as my route to the outcrops of interest. The boulder is granitic (likely tonalite for hard core igneous people). However, I know of no granitic rocks anywhere on the Olympic Peninsula. This boulder hitched a ride on the Juan de Fuca lobe of glacial ice approximately 18,000 years ago. This lobe of ice extended out beyond the current coast line and this boulder derived from the coast range of British Columbia is a reminder of that period. The distance traveled is a minimum of 120 miles.
I always enjoy seeing rocks like this one as it reminds me of great adventures I had mapping and collecting rock samples within and along the margins of plutons in the British Columbia Coast range and crystalline core rocks of the Washington North Cascades. Who knows this small boulder may be a transported fragment of the Spuzum Pluton or Scuzy Pluton.
Some how this rock was sitting alone on the beach, but there were plenty of similar rocks along the upper beach where the bluff consisted of very boulder rich glacial till.
The boulders in the sand were not the only thing that got my attention. I was not the first to walk the beach that morning. I am assuming an otter, but alas I never saw the creature that made these prints.
Dan McShane is an engineering geologist with Stratum Group, a geology and environmental consulting company based in Bellingham, Washington. Dan has been reading Washington State landscapes since driving across the Horse Heaven Hills with his father and brother in 1970. Dan's wife has started painting Washington landscapes. The intent of this blog is to help all Washington travelers better understand the landscapes we see and share field observations.