Shasta Court erratic in Coquitlam, BC

Shasta Court Erratic – Coquitlam, British Columbia

By Terry Spurgeon, Coquitlam, British Columbia. January 20, 2010

Terry Spurgeon stands on the low side of the Shasta Court erratic. Click to enlarge

This 6 metre (20 foot) high, late Pleistocene granodiorite erratic is derived from rocks of the British Columbia Coast Mountains, and was left behind by receding ice of the late Fraser glacial period. The behaviour of glacial advances and retreats of this period in the Fraser Valley and the mountains of Vancouver’s North Shore mountains is being revealed by a number of researchers whose data appears to dispel any notions of a simple ice progression to the west down the Fraser Valley. The fjord-indented southern margin of the Coast Mountains strongly suggests ice moving into the Fraser Valley from numerous subsidiary valley systems giving rise to a time-transgressive palimpsest of advances and retreats.

The erratic, located in a residential cul-de-sac, is coarse-grained granodiorite. This rock is

Detail of mineral grains in the Shasta Court erratic. white grains are plagioclase feldspar, a little gray quartz. Dark grains are mostly biotite, some elongated hornblende.

pervasive in the Coast Mountains across Burrard Inlet just north of the erratic’s location. The asymmetric erratic is approximately 14 metres long by 7 metres wide and stands 6 metres high above the surface. It is not known how much of the erratic is buried in the glacial till in which it sits.   It isn’t hard to get on top of it; the bedrock source could be the mountains visible just to the north.

Location: latitude 49° 15.961/longitude 122° 50.526, elevation 153m; UTM 10U E0511488 N5457039 (WGS 84)

To get there: This erratic is located in the Shasta Court cul de sac, east of Simon Fraser University in Coquitlam, BC. From Highway 1 (Trans-Canada), or the Lougheed Highway, proceed north to Como Lake Avenue (an east/west artery. A good route from the south or east:

-Take the Lougheed Highway (7E) exit from Highway 1, just west of the Port Mann (Ironworkers) Bridge over Fraser River.

-Stay in the left lane, and take United Blvd North.

-Keep right and turn right onto Mariner Way.

– In 3 km (1.9 miles), turn left on Como Lake Avenue

-In 2 km (1.3 miles), turn right at Poirier (traffic light and Chevron gas station)

-After 300 metres (0.2 miles), go right on Harbour Drive.

-After another 300 metres (0.2 miles), turn right on Shasta Court. There it is.

From the west, take Como Lake Road 3.9 km (2.45 miles) west of Gagliardi, and turn left on Poirier.

You can find it on Google maps by seeking 292 Shasta Court, Coquitlam, BC.

Further reading: serious erratic hunters will find several papers or books that will illuminate the complexities of the waxing, waning and sources of the ice which dropped the Shasta Court erratic and others throughout the region. The final picture will certainly prove to be more complex than ice just moving along the Fraser Valley to the coast.

Clague, John and Turner, Bob, 2003.  Vancouver, City on the Edge – Living with a dynamic geological landscape.  Tricouni Press, Vancouver, pp. 192.

Lian, O. B. and Hickin, E. J., 1993. Late Pleistocene stratigraphy and chronology of lower Seymour Valley, southwestern British Columbia.  Canadian Journal of Earth Sciences, v. 30 n. 4, pp. 841-850.

Lian, O. B. and Hickin, E. J., 1996. Early Postglacial sedimentation of Lower Seymour Valley, southwestern British Columbia.  Geographie Physique et Quaternaire,  v. 50, n. 1, pp. 95-102.

Mathews, Bill and Monger, Jim, 2005, Roadside Geology of Southern British Columbia, Mountain Press Publishing Company, Missoula, Montana, pp. 404.

Monger, J.W.H., editor, 1994.  Geology and Geological Hazards of the Vancouver Region, Southwestern British Columbia, Geological Survey of Canada, Bulletin 481, pp. 316.

Ward, B. C. and Thomson, B., 2004.   Late Pleistocene stratigraphy and chronology of lower Chehalis River valley, southwestern British Columbia: evidence for a restricted Coquitlam Stade. Canadian Journal of Earth Sciences, 41: 881-895.