Getting Started
This EarthCache is located in the backcountry of Crystal Cove State Park. The closest parking is in the Moro Canyon Area parking lot near the Visitors Center. From PCH, turn at the intersection with School - State Park (see Additional Waypoints below), and then follow the signs to the Visitor Center. There is a day use fee for parking. At the time of cache publication, it was $15. But you can easily spend the whole day exploring the beach and backcountry of this park. You can also use your receipt for this park to gain free access to any other state parks on the same day.
The location is near Trail Marker #4 along the Geology Discovery Trail (Note: This trail marker had not yet been placed when this EarthCache published). It is just under one mile from the parking lot. You may be able to obtain a Geology Discovery Trail guide at the Visitor Center (Note: There were none available at the Visitors Center when this EarthCache published). You can also view the Trail Guide on-line here (and print out your own copy to bring along if you wish).
From the northeast end of parking lot, walk to the trail head for No Dogs Trail. Hike up No Dogs Trail and then up No Name Trail. Bear left at any trail junctions along the way. There is no shade along the trail, so please come prepared with water, a hat, and sunscreen.
What’s A Geologic Column?
A geologic column is a diagram that shows the subdivisions of geological time in a particular area. For this EarthCache, we are concerned with the geologic column for coastal Southern California, and with the Vaqueros Formation and the San Onofre Breccia within this column, in particular.
Do you see the abrupt vegetation changes on the hillsides around you at this location? In many places you see boundaries between coastal sage scrub (commonly on the Vaqueros Formation) and grass (commonly on San Onofre Breccia). Since rocks differ in their mineral content, porosity, and resistance to erosion, biological species with varying needs live on different rocks.
The Vaqueros Formation
Beginning 25 million years ago, sediments (sand, silt, clay, and skeletons) slowly accumulated in shallow Pacific Ocean waters and formed the geologic layer known today as the Vaqueros Formation, the oldest exposed rock unit in the park.
The Vaqueros Formation is a sedimentary geologic unit, which is widespread on the California coast and coastal ranges in approximately the southern half of the state. It is predominantly a medium-grained sandstone unit. The sandstone unit consists of well-sorted grains, averaging medium-size, typically quartz and feldspar with some black flecks, and in form it ranges from cross-bedded to massive and thick-bedded. Occasionally it contains pebbles, especially near its base where it sits on the red non-marine Sespe Formation. Some fossils – including mollusks and barnacles – can be found in the Vaqueros, also near the base of the unit where the depositional environment was nearest shore.
Being resistant to erosion, it forms dramatic outcrops in the coastal mountains. Its color ranges from grayish-green to light gray when freshly broken, and it weathers to a light brown or buff color as it becomes a clayey soil which supports chaparral.
The San Onofre Breccia
Between 15 and 12 million years ago, sediments forming the San Onofre Breccia were deposited from islands offshore as California was torn apart by tectonic forces. Magma (molten rock) worked its way up through joints and faults, forming andesite and diabase dikes (igneous intrusions cutting across the rock fabric) and flows.
Breccia (pronounced brech-ee-uh) is a sedimentary rock composed of a mixture of broken angular fragments (clasts) of mineral or rock embedded in a fine-grained matrix (the “glue” that binds the clasts together). The fragments may range in size from fractions of an inch to bus-sized blocks. They may consist of a single rock type or of many types, as is the case with the San Onofre Breccia formation.
Logging Requirements
At the posted coordinates, face northeast. Consider all of the land in your field of view, but not including the mountain tops in the far distance.
Send me a note with:
- The text “Crystal Cove - Geology -> Biology (GC543MZ)” on the first line.
- The names of all the geocachers in your group for whom you are submitting answers.
- Is the land in your field of view predominantly part of The Vaqueros Formation or San Onofre Breccia? Why do you think that?
- What percentage of the land in your field of view is part of The Vaqueros Formation versus San Onofre Breccia?
- Is the trail on which you’re standing on The Vaqueros Formation or San Onofre Breccia? Why do you think that?
Please submit your answers when you log this cache. You do not have to wait for confirmation before logging. Logs for which answers are not submitted will be deleted.
Please don’t include the answers to any questions in your log, even if encrypted!
The following sources were used to create this EarthCache:
