Geology: The fossiliferous layers are part of an unnamed Pleistocene formation. Once you park, walk down to the beach and look for the sedimentary rocks on the beach cliff. However, the geology of the area should be similar to the Monterey formation which contains both Gaviota Beach, and Jalama Beach.
Fossils: The layers of sandstone contain marine assemblages from the Pleistocene epoch.
Geology of the Area: Centerville Beach is part of the Rio Dell Formation, giving it very similar geological history to the Scotia Bluffs nearby. The sedimentary rocks were once a mud rich layer that was deposited on the edges of a shallow sea during the Pleistocene epoch. Look for layers of grey unconsolidated mud, which will be fossiliferous and have shell fossils protruding from the surface. Low tide is the best time to look for fossils on a beach.
Paleontology/ Fossils Found: Moon Snail, Giant Pacific Scallop, Clam, Pandora shell, Cockle, Snail, Channeled Dogwinkle, and other fossils can be easily found on the cliffside of the beach.
Leslie Scopes Anderson, “Unearthing Evidence of Creatures from Deep Time,” (Humboldt U 2011) www2.humboldt.edu
Ellin Beltz, “Fossil Localities – Humboldt Bay Area,” (Field Trips by Ellin Beltz 2008) http://www.ebeltz.net
Geology: Being within the Santa Cruz Mountains in the Central Coast Ranges, Scotts Valley is a geologically active region under the influence of multiple fault lines. The valley’s bedrock is part of the Purisima Formation. Fossils obtained in the area are likely part of the Santa Margarita Sandstone. According to the Scotts Valley Town Center, “The Santa Margarita Sandstone generally consists of massive, fine- to medium-grained sandstone of upper Miocene geologic age. The Santa Margarita Sandstone forms a distinctive formation of white and yellow sand that can be observed in cliffs around the area”.
Paleontology: Marine fossils are very prevalent in the area, and it is a common area for fossil collectors to visit. Shark teeth (Mako, Megalodon, etc), dolphin, whale, sea cow, and walrus bones, and sand dollars have been found in the area. Sand dollars are especially common and should be fairly easy to spot. Here is a collection of photos of fossils recovered from the area from the Land Trust of Santa Cruz County. Recently, a four million year old whale fossil was discovered in the area. The find was covered by the article, “Whale Fossil Uncovered in Scotts Valley”.
Directions to Sand Dollar Site: One site in particular is known for its abundance of sand dollars. According to this fossil collector, Take Hwy 17 south from San Jose towards Santa Cruz/Scotts Valley. Take Mount Hermon Exit in Scotts Valley. Turn right onto Scotts Valley Drive. Turn right onto Bean Creek Road, and drive a little over a mile until you see a tall, sandy roadcut that is fairly steep. However, it is important that the area is off limits, and you will encounter ‘No Trespassing’ signs.
RMcWilson, “Fossil Sand Dollar Site in Scotts Valley, California,” (Flickr 2009)
“Approach the bluffs from an access point on the southeast side of the Rio Dell/Scotia bridge. Walk along the railroad tracks (abandoned) under Highway 101 to the Bluffs. There is no automobile access beyond the parking lot that belongs to Pacific Lumber. Check in with their guard. If you’re lucky, it’s the gentleman who knows more about the local fossils than just about anyone else in Humboldt. Park your car with him or his coworkers.
Be sure to take a knapsack or backpack as this is a hike out to the bluffs. Walk along the tracks until you can see the railroad bridge. This is where the big pelecypod mollusks (look like the Shell Oil insignia) are found in mudstone or eroding out. they can be up to about 9 inches across if complete.
Cross the railroad bridge with caution to an exposure of sandstone or sand. This is the area which produces sand dollars and concretions which contain mollusks and other fossils.” (from Fossil Localities, cited below).
Geology of the Area:
The Scotia Bluffs sandstone was deposited around two million years ago during the Pleistocene epoch. The fine to medium grained sediment has a maximum thickness of 640 m. It is part of the Upper Wildcat group and overlies the Rio Dell Formation in Humboldt County. Additionally, the cliffs are about 15 miles from the coast and are at an elevation of 550 feet.
Paleontology of the Area:
Shallow fossil marine life from the Pleistocene epoch can be found in the bluffs, with many of the species still thriving today. According to “Unearthing Evidence of Creatures from Deep Time” by Leslie Scopes Anderson, Giant Pacific Scallop (Petinopecten sp.), Clam (Thrasia sp.), Cockle Shell (Clinocardium meekianum), Sand Dollar (Scutellaster sp.), Moon Snail (Nautica clause), Pandora shell (Pandora sp.), Razor Clam (Siliqua oregonensa) and Shelly sandstone (Psephidia sp.) have been recovered from the area. See image below.
The cliffside of this beach contains shale from the Monterey Formation. The fossiliferous shale dates back to the Miocene epoch. There are talus slopes in many areas created by folded and slanted strata.
Be careful of falling shale from the cliffside. Although it poses a hazard, the fallen rocks are more convenient to split than extracting shale from the outcropping. Split fishes can be found near the bottoms of the formation. Additionally, petrified whale bone has been recovered on the beach.
As you can see in the figure above, three prominent outcroppings jut out from the Monterey formation, marked 1, 2, and 3 on figures B and C above. Figure A shows that Jalama Beach, to the left of Gaviota, is part of the Monterey Formation bearing marine Miocene fauna, and Oligocene rocks are found more inland.
Fossil fish and petrified whale bone are in the outcroppings.
The yellow brown sandstones that contain the fossils are part of the Purisma formation. Collecting is best at low tide, when the outcroppings are most exposed.
Paleontology of the Fossils:
The fossils originate from the Pliocene epoch of the Neogene period. Bivalves, gastropods, sea urchins, crabs, marine mammal bones from whales and seals can be found. Shark teeth have also been recovered from the beach, but are rare.