Coastal Erosion of Point Loma EarthCache

Enjoy the beauty of the Pacific coastline of southern California on Point Loma near San Diego; observe and learn about the erosional effects of the heavy surf upon the geologic layers. Additional sights and geocaches are nearby.

Location Information

This Earth Cache is located in Cabrillo National Monument. Visitors must pay an entrance fee at the main gate which is open from 9 AM to 5 PM. Upon entering the park follow signs to the Tidal Pool Area, the second right turn just past the main entrance gate and descending toward the coastline on the ocean side, Cabrillo Road.

Access to ground zero is via the trailhead departing from the south end of Sea Cove Parking Area. The parking area is a short drive past the Point Loma Tidal Pools Visitor Center. The Tidal Pool area closes at 4:30 PM.  A waypoint for this parking area is shown on the map. The walk to ground zero is less than a quarter mile, albeit, a bit steep. In order to best see the tidal pools and the wildlife within them it is recommended that visitors to the Tidal Pools of Cabrillo National Monument arrive during low tide; however, a low tide is not necessary to successfully earn credit for finding this Earth Cache. The information required is discernible regardless of the tide level.

I recommend that you stop in at the little visitor center manned by a park volunteer, read some of the informational signs and learn from the naturalist. (Note: answers to the Earth Cache questions don't require any information from the Visitor Center.) Safety information is provided as well. However, do not approach ground zero along the trail leaving from the Visitor Center in that direction. Drive over to the Sea Cove Parking area and use short trail that begins there.

Specific Safety Concerns

1. Wear shoes suitable for the moderate to steep descent to the coastline from the parking lot. The dirt steps cut into the hillside are uneven and tend to be slippery.
2. Along the way and, especially on the coastline, attention to your footing is a must. Watch where you step! Don’t get near the edge of the cliffs. Close proximity to the edge is not required to obtain the information for this Earth Cache.

Please do not post any answers or clues in your log. Send all answers to the questions to the cache owner via email. Best to email your answers at the same time that you log your find. Pictures are welcomed but not required for obtaining credit for the find. Also, a bit of information about yourself is always fun to read and appreciated, but not required. Enjoy your visit.

Coastal Erosion

You are on the peninsula known as Point Loma. The sandstone layers and conglomerates layers (mixture of gravels, sand and other material transported by water runoff from lands/mountains to the east) that make up this peninsula find their geological beginnings some 65 to 75 million years ago. Over the eons much material was deposited and eventually compacted. Uplifting, from deep within the earth’s crust, of the compacted and cemented layers occurred as a consequence of the compressional movement of the tectonic plates (for which southern California is famous due to the earthquake activity that they cause). These geologic processes formed the peninsula upon which you are now standing. (For a more thorough discussion of the formation of the peninsula, visit the Earth Cache, Bayside Journey to the Cretaceous, found on the other side of the peninsula which faces Coronado and San Diego.)

The cliffs, terraces, nooks, tidal pools and cutouts that define the coastline upon which you are standing are primarily the consequence of erosion of the peninsula by the ocean waves and tidal currents. The ocean facing side of the peninsula, in particular, is subject to the full force of the ocean as the wind driven waves and tidal forces hit head on. Thus, Point Loma peninsula, as you see it today, is the result of two of the most basic geologic effects, deposition, which provided the materials from which the peninsula formed; and erosion, which slowly shapes and tears down the peninsula.

As the waves crash upon the edges of the peninsula erosion is generated by…

1. the weight of the water pounding upon the land
2. the suspended materials, notably sand, scouring the solid surfaces
3. the force of air compressed by the waves prying into the cracks and crevices.

The height to which the erosional forces reach is determined by the height of the tides day by day and the level of the ocean throughout the geologic history.

Requirements of Earth Cache

In order to successfully log this Earth Cache, please send to the cache owner the answers to the following questions.

1. The effects of wave erosion are observable much higher up the sides of the peninsula than the waves can currently reach, even during high tide. How is it possible that wave erosion could have contributed to the shaping of the higher levels of the peninsula?
2. Look carefully at the dark, bare rock surfaces seaward from where you are standing. Briefly describe their texture.
3. Of the three erosional impacts of waves given above, which is most likely responsible for the texture as you described it?
4. Looking at a bare, rock cliff face exposed to the wave action, many layers of sediment are observable. What is the most prominent aspect of these layers that enable you to easily see each layer?

I hope you have found this Earth Cache informational and interesting, as well as providing a fun opportunity to observe fine Pacific coastline scenery. The information above is pulled from the educational background of cache owner, who is an Earth Science teacher, with some information gleaned from Living With Coastal Change Additionally, I wish to extend my appreciation to the park rangers who were very helpful and pleased to have another Earth Cache within Cabrillo National Monument.

Congratulations to e6b_nfo for the "First-to-Find."