3 - A Geologic Tale

WAYSIDE DESCRIPTION: The wayside is located about 80 feet south of the parking lot, just before the convergence of the forking paths that come together just south of the WWII fire control station bunker. This is one of three panels that stand side-by-side facing south west.

VIEW FROM WAYSIDE: To your left, is the railed path leading down to the overlook, on a small spit of land lined with coastal scrub and a few cypress trees. To the north, the coast curves around to a point, forming a half-circle in the space between where you stand and the point, before curving a second time, forming another half-circle further up the coast.

PANEL TITLE: A Geologic Tale. This is the panel located on the right

TEXT: Reading the landscape. This in-and-out, scalloped coastline holds clues to both ancient and ongoing stories. The landscape around you contains coastal bluffs, rocky coastline, sandy beaches, mountain ridges, valleys, and peninsulas extending out into the sea. Each part tells a geologic tale.

TEXT: The Rocks. Sticking out of the water, near shore, jagged "sea stacks" of hard basalt have endured pounding waves for millennia, as the sea eroded the bluffs around them. On land, much of the landscape is mélange, part of the defining geology in the Bay Area, the Franciscan complex formation. Melange is a crushed jumble of ancient sea floor deposits and lava erupting along cracks underwater. Massive boulders dotting the rolling landscape are its clues. Like nuts in cookies, these harder greywacke sandstone and greenstone basalts emerge from undistinguishable rubble of crushed rock and softer seabed materials to create the picturesque California coastal landscape.

DESCRIPTION OF IMAGE: A photograph of rocky, coastal cliffs on the right and blue ocean waters stretching out to the left.

CAPTION: View from here looking north. Bolinas juts out into the sea in the upper middle of the picture. You are standing on the North American Plate; Bolinas and Point Reyes, faintly visible on clear days, are on the Pacific Plate.

DESCRIPTION OF IMAGE: Dark, craggy rock jutting out from calm ocean waters.

CAPTION: Basalt "sea stacks" near shore.

DESCRIPTION OF IMAGE: Light-colored rocks on a hillside nestled amongst green scrub plants.

CAPTION: Boulders of greenstone basalt and greywacke sandstone stick out of the eroded surface rock.

DESCRIPTION OF IMAGE: A black and white photo of a woman wearing a white blouse and dark full-length skirt standing in profile on a ridge next to a long, straight crack in the ground stretching into the distance.

CAPTION: Well-known local naturalist, Alice Eastwood, standing next to crack in the earth at Point Reyes, about thirty miles north of here, shortly after the famous 1906 earthquake.

TEXT: The Moving Land. On a clear day, you'll see Point Reyes to the far north, past the Bolinas peninsula. Both of these pieces of land have been inching their way north from Monterey for twelve to fifteen million years. Bolinas and Point Reyes sit on the Pacific Plate. Here at Muir Beach Overlook, you are standing on the North American Plate. On its slowly grinding path, the Pacific Plate scrapes its edge along the North American plate while it also pushes up from beneath, forming the coastal mountains.

The famous San Andreas Fault separates the two plates and lies just offshore from here, coming onto land at Stinson Beach, about ten miles to the north. Driving along Highway 1 for forty miles north from here, you can follow this famous fault along Stinson Beach and Bolinas Lagoon, through the Olema Valley and along Tomales Bay.

MAP OVERVIEW: A map of the California coast from Point Reyes National Seashore to the north down to San Mateo County south of San Francisco. The map also includes the San Pablo and San Francisco Bays to the east. San Pablo Bay is to the north of San Francisco Bay.

MAP DESCRIPTION: The land areas on the map are mostly a light tan, with some areas colored two distinct shades of green. The darker green represents NPS-managed Golden Gate National Parks lands, and includes areas north of Bolinas Ridge, the eastern side of Olema Valley as well as areas further south including Muir Woods, the Marin Headlands, Tennessee Valley, Muir Beach, Muir Beach Overlook and a northern section of the San Francisco Peninsula. The lighter green represents land within the authorized boundary of the Golden Gate National Parks and includes areas around Mount Tamalpais State Park north of Muir Woods, as well as land to the north and east including the Marin Municipal Water District and areas east of Bolinas Ridge. To the south, in the middle of San Mateo County, is a swath of light green with a small strip of darker green in the north western section. Running diagonally north west to south east is a red dotted line representing the San Andreas Fault. The fault line cuts between Point Reyes and Bolinas Ridge, through the center of Olema Valley on down along the ocean, just west of Stinson Beach, Muir Beach Overlook, Muir Beach, Tennessee Valley and the Marin Headlands. The fault continues through the ocean until it comes aground again just south of San Francisco and continues its path down through San Mateo County.

TEXT: The San Andreas Fault lies under the water just offshore. The fault line comes on land just north of here at Stinson Beach, and proceeds north through the Olema Valley and Tomales Bay.