Intro: Welcome to a little-known, hard-to-get-to, but oh-so-beautiful spot along the California Coast. This is Black Sand Beach. This rare spot will take quite a bit of driving (or other transportation!) to reach, but there are two options. I made it a loop when I visited, entering from Ferndale, and exiting out through Honeydew.
KNOW BEFORE YOU GO: As stated above, this location requires a long drive. Begin the drive with a full tank of gas! There are no services nearby this beach and it is NOT a well-traveled area. There is also no cellular phone service. If stuck, you could be stranded for several hours or more. With that all being said, this spot still comes to you highly recommended from myself and is most definitely worth the adventure out here when done safely.
The Spot: The coordinates bring you to a arbitrary point along the beach. The black sand runs for over a mile at this point, and Mattole Road runs right along it for a solid stretch. The black sand even pops up for other stretches further down south. This stretch where Mattole Rd parallels the beach has parking available right off the side of the road at multiple different spots (including right near these coordinates). Any of these pullouts will do, as you will have access to the beach.
The Sand: Black sand is not very common to see! Most beaches around California and even the world contain a classic tan/white sand that most of us are used to seeing. Black sand can form on beaches in three main ways. We will briefly cover the first two, and although they do not directly explain the presence of black sand here, they help paint some context for understanding dark-colored minerals that can find their way into sand anywhere.
The first way black sand beaches form is due to volcanic activity. This is the case for the black sand beaches that are commonly shown around Hawai’i and other volcanic islands (the Canary Islands, the Aleutians, etc.). Volcanic islands have dark-colored rocks like basalt, andesite, and volcanic glass. These rocks contain minerals that give them their distinct black color. Due to the high mineral content in these rocks (such as iron oxides), these rocks and grains of sand are heavier than light-colored sand and can absorb a lot more heat.
Another way black sand can appear on beaches is simply through the deposition of dark-colored rocks onto the beach. Heavy mineral sands are more resistant to weathering and can be carried high up on a beach by strong waves and currents. Small or large streaks of black sand appear when this washed-up sediment successfully avoids getting washed back into the ocean with the waves. Although these heavy mineral sands are full of a spectrum of colors if you look closely, the contrast between them and the light tan sand makes it appear as black sand.
Lastly, black sand can be present as a result of the underlying geology of the immediate area. Excluding deposited sand (aka outside sources), the type of sand present on a beach is determined by the geologic makeup of the immediate area. This is the case for Black Sand Beach. This stretch of coastal California is made up of Late Mesozoic eugeosynclinal rocks of the Franciscan Formation. The Franciscan Formation is a diverse complex of sediment comprised of all three types of rock (igneous, sedimentary, and metamorphic).
The Franciscan Formation contains basalt (igneous), which formed in this complex from submarine lava flows.
The Franciscan Formation also contains greywacke and chert (sedimentary). Greywacke is sandstone that is full of a lot of other angular rocks, leading it to often endure being called “dirty sandstone.” Chert appears as thin, red-colored bands in the complex, leading it to be called “ribbon chert.”
Lastly, the Franciscan Formation contains serpentine (metamorphic). Serpentine forms as an alteration of ocean crust and upper mantle rocks, containing high levels of magnesium and iron.
All these types of rocks and more make up the Franciscan Formation, which is the source for the sand at this beach. Through weathering, erosion, and other natural coastal processes occurring at all beaches, bits of the Franciscan Formation are gradually broken down into the sand we see here today.
To log this Earthcache:
Send me a message with the following:
- The name of this earthcache and the number of people in your group
- Pick up a handful of sand and make some observations about what you see. Describe the shape of the grains, and how coarse the sand is (fine, medium, rough).
- Looking closely at your scoop of sand, do you notice any other colors?
- Of the four main rock types in the Franciscan Formation covered here, which one(s) do you think contribute to the black color of the sand?
Sources:
-https://www.geocaching.com/geocache/GC8ABB6
-https://www.visitredwoods.com/listing/black-sands-beach/525/
-https://www.sandatlas.org/what-is-black-sand/
-https://www.researchgate.net/figure/Geological-rock-formations-map-of-California-United-States-Geological-Survey-1966_fig7_304675732
-https://ucmp.berkeley.edu/education/calandscape/session3/franciscan.html
Thank you, and enjoy your visit! Please post as many pictures as you want!