SWAMI'S

The Del Mar Formation is the major rock unit exposed in this area. Note that the cliffs are being undermined and are dangerous.
The formation has been dated upper Eocene in age by the abundant fossils found in several layers of the formation.
The formation has been dated upper Eocene in age by the abundant fossils found in several layers of the formation.
The formation consists of alternating beds of sandstone, shale, and siltstone, indicating a near shoreline environment of deposition.
The presence of abundant carbonaceous material and what appears to be sulfer, indicate that at times, the environment was similar to that of a lagoon filled with much silt and organic debri.
Some layers consist almost entirely of fossil remains, indicating a shallow water marine environment.
Some layers consist almost entirely of fossil remains, indicating a shallow water marine environment.
The contacts between the various rock layers, mark changes in the depositional environment.
One might invision a site of deposition where sea level was fluctuating between a brackish water, silt laden, shallow water environment, similar to that seen in the nearby lagoons today
to a relatively shallow water marine site of deposition.
Sedimentary rocks that may be collected, include poorly cemented sandstone, shale and biostrome (a rock containing abundant organic remains)

Metamorphic and igneous cobbles are abundant on the beach
The rock outcrops undergo weathering to produce a finely divided sand with abundant biotite. This raises a question as to the origin of the beach cobbles as they bear no resemblance to the rocks found in the immediate area.
The longshore currents provides a clue to their source. Waves breaking at an angle to the shoreline forces water up onto the beach. The water returns to the sea by the shortest route, which is at right angles to the shoreline. This results in a movement of water along the Shoreline. We find that the prevailing longshore current is to the south. If we travel north, we may find the source of the cobbles.
This reef is an outstanding feature of this area. It is an erosional remnant of a former beach terrace. Its composition such that it is more resistant to weathering and erosion than the rest of the rocks making up the original terrace
Waves converge on points such as these tending to straighten the shoreline. It is the convergence of such waves that make this a popular site for surfing.
Some of the rocks near the reef contain abundant pelcypods.
The reef is marked by numerous small potholes. This is believed caused by etching of the rock by acids. Organisms in standing water, remove oxygen and in-crease the concentration of carbon dioxide forming carbonic acid which reacts with the rock
Many worm trails and casts may be found in some of the rocks.
Here more worm trails and casts may be seen.
This is the location where fossils which date the Del Mar formation are found in abundance.
The fossils are located in a tan  sandstone about 20-30 feet above the beach.

Among the fossils are Gastropods- Turratella avasana, applinae & Sinum obliquam
Also fossil Pelecypods-- Venericardia horni
And Macrocallista horni
All along the cliffs seepage of ground water may be seen. The water perculates downward until impearmeable rock layers are incountered. The water then migrates to the cliff, where it seeps out.
In many places salt crystals form when the mineral laden ground water evaporates.
Walking northward toward Moonlight beach, one can see what appears to be a large arch of rock .(anticline)
At one point it appears that the Del Mar formation wedges out, disappearing from view beneath the surface of the beach. Note that the sandstone in the Del Mar formation contains fossils 20 feet higher to the south.
We look closely at the rock at this point and find that it consists of a massive sandstone, with cross bedding a predominant feature. Where have we seen this type of feature before?
This is a slide of the Torrey Sandstone formation, located in the Del Mar Heights area. The cross bedding is more pronounced due to weathering.