The Pigeon Point Lighthouse has long kept a lonely vigil along the rugged coastline of San Mateo County, protecting ships from the fate that befell the clipper Carrier Pigeon, which capsized here in 1853. But even as a century and a half of harsh elements ate away its bricks and iron and modern seafaring technology, rendering it a mere anachronism, preservation advocates and the California State Parks have joined together on a multiyear project to save the tallest lighthouse on the West Coast of the United States.