Rocks In Rocks – Discovering The Cool & Wacky World Of Concretions

July 25, 2012 by libertatemamo 11 Comments

Sometimes you discover something that is SO ÜBER COOL you just have to find out everything about it. This happened to me a few weeks ago as I was writing about our visit to Cape Arago and discovered this post about concretions. I had never heard about these things and was immediately intrigued. A rock that grows inside another rock? The creation of outlandish spherical bulbs of all sizes? Rocks that contain fossilized matter inside? Rocks that grow to be as big as a person? Landscapes of giant rocks that look like outer space?

OMG…this is the most totally cool thing EVER! I was hooked and absolutely, positively needed to find these things and see them for myself.

Thus began a 2-week expedition of “concretion hunting” with some fun exploration and exciting pictures to boot. Not only have I discovered the best local hiding spots around Charleston and Shore Acres, but I’ve learnt alot more about these unusual and fun geological structures.

So what exactly IS a concretion? Structurally they are compact masses of mineral matter embedded in a host rock of other matter. They typically start to form around a “nucleus” of some sort (a shell, a crab, a leaf whatever) and grow inside cracks and cavities of other rocks or get buried in sediment that then hardens. The net effect of all this is a rock within a rock….or more specifically one type of rock inside another type. Surprisingly they are actually really common, but for a non-geologist like me finding these things is akin to the discovery of chocolate sauce on ice cream -> a totally delicious revelation!

So now that I’ve got you all hot and bothered to see them, where do you actually go to find these hidden gems? The area around Charleston & Shore Acres actually has 5 excellent spots with concretions of all sizes, two of which I discovered with my cousin and one (“the giants”) that I scoped out yesterday with our RV buddies Lu & Terry (Paint Your Landscape) who just rolled into town. They are ALL worth visiting and these are my top picks (map at bottom):

1/ “The Giants” at Fossil Point -> Humungous man-size concretions that are best seen at absolute low tide. Going north from Charleston, cross the bridge and drive ~1.8 miles along Cape Arago Hwy. Park at the first turnout on your left after Fossil Point road. Hike around the point to the south until you see the monsters. This is also a great spot to hunt fossils, as you’d expect. Be prepared for mud!

2/  “The Wall” at Yoakam Point -> A spattering of softball-size concretions on a cool wall that juts into the ocean. These are also best seen at low tide where more of the beach is open to walking. Going south from Charleston along Cape Arago Hwy, drive past Oceanside RV Park and take the first turn-out on your right a little ways up the hill. There are several poles and the entry to a trail, but no signs. Follow the trail to the beach and go right from there to see the wall.  The beach here is also, incidently, one of the best places to get a view of closed-to-the-public Cape Arago Lighthouse.

3/ “The Line & Seat” at Simpson Beach -> A really cool line of ground concretions and interesting wall-set big enough to sit on. Simpson Beach is reached by trail directly from Shore Acres State Park. Simply take the trail to the beach and walk to the south end to see the concretions.

All in all a good few weeks hunting with a darn good set of catches. The cool and wacky world of concretions is just as fun in person as they are in print, so if you haven’t yet been seduced by these rocks, I’d recommend letling yourself go and giving it a try. Fun, discovery and rocks to write home about. Priceless!