Sands sorted by a receding tide, as water drains off the beach and back to the surf line. Grains of magnetite, quartz, feldspar and other remnants of glacially eroded ancient Sierra sediments, combine to make intricate patterns reminiscent of wood grain in the beach at Ft. Funston.
Two distinct sediments mixed and laid out in a pattern by the waves at Ft. Funston. The black is an iron rich magnetite, deposited in a dense layer half a million years ago when Mt. Lassen erupted. The lighter, golden sand was left behind 10,000 to 15,000 during the Wisconsin Ice Age. During that time the shoreline as we know it had moved westward about twenty miles. As the Ice Age ran its course and the planet warmed the shoreline moved back east, bringing with it massive amounts of the sand you walk on today at Ocean Beach and Fort Funston. These two remarkably different sediments mix on the shore of Fort Funston’s beaches. The magnetite eroding from a sedimentary layer in the bluffs, and the sands of glacier ground granite, brought here by the Sacramento River long ago are sorted by wave action to create dramatic patterns.