Observatory count and track this fall migration using bird-banding and radio-tracking techniques, all in cooperation with the National Park Service. Wildlife The Marin Headlands are also home to black tail deer, mountain lions, bobcats, two types of fox, coyotes, wild turkeys, hares, rabbits, raccoons, and skunks. In 2003, there was a reported sighting of a black bear in the Headlands; the report was lent credence by a 2012 finding of bear scat on a hiking trail in the Kent Lake watershed, and another sighting on the Point Reyes National Seashore in 2011. River otters inhabit the freshwater lagoons and streams. Large numbers of water birds also migrate through the Headlands, including brown pelicans from May through October; and grebes, egrets, and great blue herons in the spring, summer, and fall. The Headlands' status as a park protects the habitat and populations of these animals within just a few miles of San Francisco and its suburbs. In the waters surrounding the Headlands, harbor seals can be found year-round, gray whales can be seen in the spring and fall, and seabirds such as common murres and surf scoters swim within sight of shore. When Richard Henry Dana, Jr. visited San Francisco Bay in 1835 he wrote about vast elk (Cervus canadensis) herds on the Marin Headlands on December 27: "...we came to anchor near the mouth of the bay, under a high and beautifully sloping hill, upon which herds of hundreds and hundreds of red deer [note: "red deer" is the European term for "elk"], and the stag, with his high branching antlers, were bounding about..." Geology The Marin Headlands are underlain by geological formations created by the accretion of oceanic sediments from the Pacific Plate onto the North American Plate. The process of subduction of ocean floor, followed by tectonic underplating to the underside of the over-riding plate, was first described here by Clyde Wahrhaftig in 1984. The primary rock types of the Marin Headlands include graywacke sandstone, radiolarian chert, serpentinite, pillow basalts, and shale. These rocks began their migration over one hundred million years ago from as far south as present-day Los Angeles. The erosion of the hillsides and construction activities during the military era have exposed some dramatic examples of these rock types for easy viewing, and the folding caused by tectonic action is visually evident in many places throughout the Headlands. Marin Headlands is one of the featured