Located within the confines of Shore Acres State Park, this area is the former estate of early-20th-century timber magnate Louis J. Simpson. Perched on rugged cliffs high above the ocean, the park is an exciting and unexpected combination of beautiful geological and constructed features.
You will need to stroll down the trail to the secluded ocean beach called Simpson Cove to visit the earthcache. The earthcache is low tide dependant so please check the tides at the ranger station before hiking down to the cove. No dogs or other animals are allowed outside vehicles. There is a $5.00 fee per vehicle Parking Fee.
What on earth is a concretion?
Concretions:
The word "concretion" is derived from the Latin words "con" – meaning "together" – and "cresco" – meaning "to grow."
A rock that grows? Is there really such a thing?
A concretion is a compact mass of mineral matter, usually spherical or disk-shaped, embedded in a host rock of a different composition. This hard, round mass of sedimentary rock cement is carried into place by ground water. They usually form early in the burial history of sediment, before the rest of the sediment has hardened into solid rock.
Concretions occur when a considerable amount of cementing material collects locally around a nucleus, often organic, such as a leaf, tooth, piece of shell or fossil, dead and/or decade matter - like a crab or fish. Most concretions form around marine invertebrates...but are not limited to marine life.
They vary in size, shape, hardness, and color, from objects that require a magnifying lens to be clearly visible to huge bodies 10 feet in diameter and weighing several hundred pounds. Concretions are world wide and very common, but here in Oregon, the largest concentration of concretions are found throughout the Cape Arago Headland.
Concretions are commonly misunderstood geologic structures. Descriptions dating from the 18th century attest to the fact that concretions have long been regarded as geological curiosities. Concretions are often mistaken for dinosaur fossil eggs, turtle eggs, or shells, or bones, human artifacts and even extraterrestrial debris. They are actually not fossils, artifacts, or even debris from space, but a very common geologic phenomenon that occurs in all types of sedimentary rock; which include sandstone, shale, siltstone, and limestone.
This diagram shows how a concretion forms by localized cementation of sand grains. The usual conditions required to form a concretion are pore waters over-saturated with respect to calcite, the presence of a seed of calcite, perhaps a shell fragment, on which more calcite can grow. It begins with sand deposited below sea level. Shallow ocean water is saturated with respect to calcite, but it often requires a mollusk, urchin or coral to induce calcite to precipitate.
To qualify as a "find", email (do not post online) the answers to the following questions and perform the following tasks. Failure to do that in a timely manner will result in a log deletion.
Follow the trail to Simpson Cove and the earthcache coordinates. They will bring you to an interestingly shaped concretion.
1) What shape does the concretion remind you of? Guesstimate its size.
2) Which type of sedimentary rock do the concretions appear to be hosted in, sandstone, shale, siltstone, or limestone? Please give your reason why you choose that type.
3) Optionally UPLOAD a photo clearly showing, yourself, your GPSr and your favorite concretion in the cove and attach it to your found log.
We hope you have learned a thing or two about concretions and thanks for visiting Shore Acres State Park.
Oregon law prohibits removing concretions that are embedded in a host rock. It is illegal and can be punishable by law. If the concretions are not attached to its host rock, then collecting is permitted, as long as they are collected by hand, and no tool or machinery is used to collect them and get them back to your vehicle.