IMPORTANT:
This is an Earthcache. There is no physical cache at the coordinates provided. In order to log a "Found it" for this cache, you must send the answers of the questions below to the cache owner via the message center or email function of the site.
------
Materials needed for this Earthcache: Camera, GPS
There is a fee required to park in the lot. However, you can walk or bike in for free. It is also recommended to download this cache beforehand, cell signal can be spotty.
------
Learning Objective: This Earthcache aims to teach you about the dunes and geologic history of Dillon Beach and the surrounding area, including the San Andreas Fault.
------
Sand Dunes: Ever Moving Mountains
The sand dunes of Dillon Beach are always moving, constantly being sculpted by the wind. There are actually two layers of dunes here - two dune “sheets” of different ages. The top sheet, light colored and younger, is always shifting. These young dunes are constantly being reconfigured by water and wind. Underneath this mobile and young dune layer, though, is a much darker and more stable deposit. This dune sheet is much older and almost inactive. It can be recognized as it is almost black compared to the light sand of the younger dunes.
The Dillon Beach dunes. You can see the darker, older layer of sand in this band underneath the newer dunes.
------
The San Andreas Fault and the Sonoma-Marin Coast
The San Andreas Fault, which runs approximately 750 miles from Northern California to Southern California, carves out the Sonoma and Marin coastlines that we know today. The fault is a “strike-slip” fault, meaning that the Pacific Plate and the North American Plate are slowly sliding next to each other. The plates move at about the rate your fingernails grow, with the Pacific Plate moving in a northerly direction. The Pt. Reyes Peninsula is situated on the Pacific Plate, which means that about 10 million years ago, at the beginning of the Pliocene, the rocks of Pt. Reyes would be about 80 miles south of their position today. It is this fault that carves out the long, narrow Tomales Bay and divides the Pt. Reyes Peninsula from the rest of the coastline. By looking across the beach to the tip of Tomales Point, you are standing on the very edge of the North American Plate, viewing the Pacific Plate only a short distance away.
You can view the tip of Tomales Point across the water, which is actually on the Pacific Plate! Dillon Beach is situated right on the San Andreas Fault, which divides the Pacifc Plate from the North American Plate.
------
Questions
In order to log this Earthcache as a "Found it" you must send the answers to the following questions to the cache owner via the message center or the email function of the website. You do not need to wait for a response from the cache owner to write your log.
Logs without answers may be deleted without notice.
#1: If you are sending in answers for a group, include the usernames you are sending answers in for. If it is just you, simply put your username at the top of the message.
#2: Look over at the sand dunes lining the beach. How do you think these dunes formed? Will these dunes be exactly the same in 100 years, or will they have changed?
#3: Describe the size of the sand grains. Are they well sorted (all the same size) or poorly sorted (many different sizes)? Describe the color and texture of the sand.
#4: Knowing that you are standing on the edge of the San Andreas Fault, how do you think Tomales Bay (the bay at the end of Dillon Beach) was formed?
#5: Take a picture of you or a personal item at the coordinates of the cache. For example, a picture of your water bottle with the beach in the background will suffice, but just a picture of the beach will not.