Stanley Park's forested peninsula juts into Burrard Inlet. Winter storm waves from the Strait of Georgia have eroded the western side of the park exposing its bedrock foundation. The popular seawall walk is a great place to observe the park's geology. Layered sandstone underlies much of the park while volcanic rock forms the prominent cliffs at Prospect Point and Siwash Rock.

Volcanic Intrusions: The Cliff Makers

Rugged volcanic cliffs at Prospect Point contrast with adjacent smooth sandstone slopes. The weak sandstone erodes easily compared to the erosion-resistant volcanic rock. Stanley Park peninsula likely owes its present size to this resistant northern tip of volcanic rock. Without it, storm waves might have long ago eroded away the soft sandstone.

Prospect Point is a sheet-like intrusion (dyke) that formed when melted rock rose along a steep fracture in the sandstone. This 30 million year old volcanic intrusion is similar in age to the Black Dyke on the Stawamus Chief.

The cliffs of Prospect Point display fracture columns (columnar jointing) formed by contraction during rapid cooling of liquid rock to a solid.

The cliffs of Prospect Point reflect the resistance to erosion of hard volcanic rock. The rock is a fine grained and dark-coloured basalt.

Siwash Rock is a famous rock pillar along the seawall route. It is a remnant of a rocky point of resistant volcanic rock that was breached by wave erosion.

Sandstone: Ancient Rivers

Green algae covers layered sandstone exposed in the intertidal zone at Ferguson Point. Wave erosion of layers with differing hardness has created the ribbed texture on the rock surface. Originally horizontal, these sandstone layers have been tilted to the south by the uplift of the North Shore mountains relative to the Fraser Valley.

Sandstone exposed in cliffs along the seawall formed as layers of sand on the floor of an ancient river. Fossilized pollen in the sandstone indicates that the sand was deposited between 87 and 35 million years ago, a period of Earth history that saw the demise of the dinosaurs and the ascent of mammals. Though no dinosaur bones have been found in these rocks, small tree fragments preserved as coal are common.

Turning this pebble-rich sand into rock involved deep burial in the Earth and deposition of mineral cement from circulating groundwaters. Deep burial was caused by continued deposition of several kilometers of overlying sediments within an ancient basin, similar to the modern Fraser Valley. Later uplift brought these sedimentary rocks back to the surface.

Through the Microscope

Stanley Park sandstone is an aggregate of grains of the minerals quartz (q) and feldspar (f) and tiny rock fragments (r). The grains are loosely held together by mineral cement composed of calcite (c) and clay.