Collecting, altering, defacing, etc. natural features, fosils, etc. is prohibited at the State Park.
The lowest layer in the cliffs is the Delmar Formation. This Formation is made up of greenish yellow siltstone and mudstone with layers of shells. The thin single layered shells are clams and the multi-layered shells are oysters. There is also some sandstone in this formation likely washed in from offshore barrier islands during storms. These rocks were deposited in a lagoon like setting with lots of animals and usually quiet waters about 45 to 50 million years ago.
The next layer is the Torrey Sandstone. As the name implies, this is a sandstone made up of mostly quartz grains. It is actually usually white, but is often stained light brown from the eroding material from the rocks above it. This layer was deposited in a sand bar, probably an offshore barrier island, about 45 million years ago.
The Formation at the top of the cliffs the Bay Point Formation. This formation is a light brown poorly cemented sandstone that was deposited about 120,000 years ago.
It is the two lower formations, the Delmar Formation and the Torrey Sandstone that tell the advancing shoreline story. These two Formations can be found for miles inland from the shore. As you noticed, they were both deposited at about the same time about 45 million years ago.
At that time, this area is thought to have looked much like the coast of Texas, coastal lagoons with off-shore barrier islands. The Delmar Formation would be forming in the lagoons, while the Torrey Sandstone was forming in the barrier islands. Diagram Source: Department of Geological Sciences, Salem State College, Salem, MA, (
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Now, in order for these localized areas of rock formation to turn into large formations that are found far inland and to get the barrier island rocks on top of the lagoon rocks, there must have been a gradual rise in sea levels.
The lagoon and barrier islands occur at specific elevations relative to sea level. So as the sea level rises, the lagoon and barrier islands move inland at the same rate. The result is that the barrier islands will eventually migrate over the location where the lagoon was, and the lagoon will gradually inundate dry land.
Sharp and Glazner liken this movement to a pair of asphalt pavers (the ones that spit out a constant layer of asphalt along new roads). One paver lays down the lagoon sediments as it moves inland followed by the barrier island paver.
An animation of this process is shown here (
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In this kind of sedimentary deposition, the rock furthest from the shore is younger than the rock closer to the shore even though it is in the same formation. So the rocks you see in the shore cliffs are older than the same rocks you can see in the road cut along Torry Grade on the inland side of the park.
Vertically, the rocks above are still youngerthan the rocks below. So in both the road cut and the shore cliffs, the Torry Sandstone is younger than the Delmar Formation directly below it. However, this is may not be true when comparing the age of the Torry Sandstone you see in the shore cliffs to the Delmar Formation further inland.
Further inland, the contact between the Torry Sandstone and Delmar Formation is at a higher elevation than at the shore. In addition, a portion of the Delmar Formation is at the same elevation as the Torry Sandstone at the shore. Referring back to the pictures of the lagoon and barrier island, you can see that the lagoon material deposited at the same elevation as barrier island material is the same age. In this case the lagoon was further inland and the barrier island was out by the shore cliffs. The Torry Sandstone in the shore cliffs (or what used to be further offshore) is approximately the same age as the Delmar Formation further inland.
As a note: you can also find a variety of other fosils and sedimentary features as you walk along the cliffs and up the trails.
The above information was compiled from the following sources:
Geology of Torrey Pines State Reserve By Don Grine, Geophysicist Emeritus, Torrey Pines State Reserve 2006, (
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Robert P. Sharp and Allen F. Glazner, Geology Underfoot in Southern California, Mountain Press Publishing Company, 1993
Department of Geological Sciences, Salem State College, Salem, MA, (
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