Annie’s Canyon is a very unique spot in the greater San Diego area. It is a slot canyon that has been carved through Torrey Sandstone by erosion. This canyon can offer difficult terrain to those who are less sure-footed. It consists of over a mile of walking, steep inclines, and narrow slot canyons that can trigger claustrophobia. Back in the day, it was known as Mushroom Caves, a hotspot for graffiti and vandalism, and was closed off to the public. Eventually some local residents took the area under their care, and cleaned it up to make it an enjoyable place for all. It is now open as a San Diego county park.
The Torrey Formation (Torrey Sandstone) dates back to about 49 million years ago. The sandstone here is composed from beach and offshore sand bar deposits, when this inland area was still in the ocean’s grasp. This layer settled when it was slightly exposed as a sandbar surrounded by water. Not many fossils can be found in the Torrey. The Torrey Formation can appear as white or have a slightly red hue due to iron oxide.
Erosion is the breakdown and removal of rock by exogenic processes. Exogenic, meaning outside, explains that erosion is caused by outside processes, like wind of water flow. Not to be confused with weathering, erosion, breaks down the rock or soil, and transports it to a different location. When it is done being moved, the leaving-behind of the rock is called deposition. Eroded sediment may be transported a few millimeters, of for many hundreds of kilometers. Weathering is simply the breakdown or color change of rocks caused by weather, but still remaining in the same place. As soon as these broken sediments are moved, it is considered erosion.
To log this earthcache, please send me a note with the following:
- Name of this cache with the number of people in your group
- How do you think this canyon was formed by erosion (wind, water, etc)?
- Run your hand along one of the canyon walls. What does the rock consistency tell you about why erosion was particularly effective here?
Sources:
https://www.fleetscience.org/phenomena/water-carves-slot-canyon-near-solana-beach
https://thenaturecollective.org/location/annies-canyon-trail/
https://gotbooks.miracosta.edu/fieldtrips/index.html
https://californiathroughmylens.com/annies-canyon/