Ruby Beach on the coastline of Olympic in Washington is famous for its impressive sea stacks and tree-topped offshore islands. In the wake of a low-pressure system moving in from the Pacific Ocean, the sunsets can be particularly spectacular.
Today’s coastline of northwestern America is the result of a still-ongoing complex geological process that has step by step piled up Alaska, British Columbia, Washington, Oregon and California from the seafloor during the last 150 million years. Geologically speaking, this region does not belong to the primordial craton of the American continent. Wandering microcontinents from afar and seamounts, along with parts of the seafloor itself, collided with America during the incessant seafloor drift of the Pacific Ocean plate. Such land masses of different rock compositions are called terranes. Today, the Juan de Fuca oceanic plate, a broken-off and rotated fragment of the Pacific Plate, subducts beneath the continent, giving birth to the volcanoes of the Cascade Range.
Erosional forces counteract this process. The 20-million-year-old Hoh sandstone along the Olympic coastline is permanently attacked by waves, resulting in huge, tree-topped sea stacks. The surf-rounded black pebbles are flysch, a steeply tilted tectonic mélange scraped off the ocean floor during the subduction process – the growth of the continent.
