Saturday, October 3, 2015

Field Trip: Agate Beach, Patrick's Point, Humboldt County, California

Overlooking Agate Beach
Agate Beach, at Patrick's Point in Trinidad, is a well known collecting spots for..... yep, beach agates. Surprise, right?

Directions:  Approximately six miles north of Trinidad on Hwy 101, exit at Patrick's Point State Park. Follow the signs to Agate Beach Campground and park by the top of the staircase. (Day use fee applies at this site).

The trail down to the beach is long and full of switchbacks, but the views are gorgeous, and the rocks worth the walk.

Winter is by far the best season for any beach combing, but I visited in August and still found plenty of agates.

At the bottom of the stairs, you'll see a small stream that flows out into the ocean. In the gravel at the mouth of this stream is where most of the agates are concentrated. Campers regularly hunt for them, so for the best finds, rise early in the morning and get the gravel that has been freshly churned and exposed by waves all night.

You'll find plenty of the usual clear/white breach agates, as well as carnelian (orange or red agate), moss agate, and plenty of colorful jasper. I've even heard claims of jade pebbles being found, though I cannot personally verify this one.

Be sure to bring a bag to carry your pebbles in -- they fall out of pockets easily, and it's likely you don't have pockets big enough to carry everything you'll end up wanting to take home.

Happy hunting, rockhounders!

Wednesday, September 9, 2015

Field Trip: Moonstone Beach, Trinidad, Humboldt County, California

Moonstone Beach
As the name implies, this beach (along with many others along this coastline) often produces agates. However, that's not what this site is primarily known for -- instead, come for the fossil shells! You will find an entire bluff filled with shell fragments. Many are fragile and difficult to remove intact, but with a little time and care, you can find quite a quantity of good fossils.

Directions: From the town of Trinidad, go south on 101 for about 2  miles. Take Kay Ave (Exit 726), turn left onto 6th, and right onto Westhaven Road. Follow that until you reach Scenic Drive, and turn left. You'll then find Moonstone Beach Road on your right, which leads you to the parking area right on the beach. Go north on the beach a short ways and climb the bluff.

Difficulty: Mostly easy, but short steep climb at the end.

Equipment Needed: Rock hammer, chisel, paper for wrapping/protecting specimens. Boots with good tread are a must for the final climb.

Safety Hazards: Don't slip.

The fossil bluff
 In the photo above, see the brown cliff face poking out between the trees? This is the fossil deposit. If you walk along the rocks below, you should be able to find the trail leading up (it can be difficult to spot at first glance).

 You'll find a narrow, steep path that climbs beneath trees and brush. You may have to duck a bit, but the path is well-worn, so you won't be at risk of wandering off it. It's steep, but relatively short.

Fossil bluff
 Once you reach the top, you'll find the entire bluff of fossil shells at your fingers. Here, the difficulty is not FIND the fossils, but deciding which ones you want to dig out and take home!

These fossils are from the Pleistocene Epoch, about 700,000 years old -- quite young for fossils, geologically speaking.

Closer view of deposit
 Many may disintegrate at first touch -- don't be disheartened, as there are plenty of harder ones as well. They may take a little more time to find.

View of the beach from collecting site
 I found numerous bivalve fossils, crab claws, sand dollars, snails, and a surprising number of what appear to be fossilized sea sponges. You can see the final haul I ended up bringing home, below.

Hope you enjoy the trip. Happy hunting!

Saturday, August 22, 2015

Field Trip: Laytonville Quarry, Laytonville, Mendocino County, California

Quarry, as seen from parking area
The Laytonville Quarry, also called Longvale Quarry, is famous among rock hunters and geologists, for being the Type Locality (original discovery site) of the three minerals Deerite, Howieite, and Zussmanite.  (Side note: these three minerals were discovered in 1965, and named after the authors of this book: Introduction to the Rock-Forming Minerals)

Difficulty of access: Near highway, trail is easy, but you need to be able to do the 50-foot sprint across a four-lane highway very quickly.
Trail is difficult to spot, but it's to the left of the sign, near the big rock
Materials Found: Rare minerals Deerite, Howieite, and Zussmanite, as well as small but well-formed pyrite cubes, and masses of small garnets.
Howieite (black crystals)

Equipment Needed: Hiking boots, water bottle, rock pick, safety glasses, sun hat, backpack for carrying specimens.

Safety Issues: Site is somewhat remote and gets extremely hot in the summer. Beware of heat exhaustion, take plenty of water and cool off in the shade when you can. Rattlesnakes are an issue, as are black widow spiders -- be careful of where you put you hands and feet, and wear boots that protect your ankles. Dead grass and loose rocks make steeper portions of the path extremely slippery.

Directions: Site is approximately 17.5 miles North of Willits on Highway 101. You will see a large pullout on the left side of the road -- this is the parking area (It's generally safest to proceed up the road a ways to find a spot to turn around before attempting this).
If you'd like a list of other minerals found at this site, check here.
And if you'd like to do further reading on the subject, I recommend: Geology of the Covelo/Laytonville Area
Good luck and happy hunting!

Saturday, July 18, 2015

Understanding Fossilization

Fish fossil, Jalama Beach, California

Fossilization is a topic that is often poorly understood among the rockhounding community. At nearly every club meeting or field trip, there is always somebody picking up a random rock with quartz veins running through it, and insisting it is a fossilized animal of some sort. Or finding concretions and wondering if they are petrified dinosaur eggs.

I hope that by reading this, you will come away with a better idea of just what fossils are, where to look for them, and how to identify if you have actually found something special.

What is a fossil, exactly?
A fossil refers to the remnants of living organisms which have been preserved in the form of stone. Usually, it refers to the preserved organism itself, though it can also be applied to traces left behind, such as fossilized footprints, burrows, or coprolites.

Geologic environments
Fossils are found in sedimentary rocks. Ancient seafloor deposits, sandstone, mudstone, limestone, or volcanic ash deposits -- this is where you want to search. Very VERY rarely, a fossil will be found in metamorphic stone, but only if that stone was originally sedimentary to start with. Usually, when rocks metamorphize, any fossils contained will be so deformed as to be unrecognizable, but occasionally one will retain enough shape to still be identified as such.

You will never find fossils in igneous rocks. [Volcanic ash deposits are considered sedimentary].

Types of fossilization

So how do fossils form? Well, that depends a bit on exactly what type of fossilization has occurred. 

  • Petrifaction: The original material is slowly replaced by minerals which gradually seep in from the surrounding matrix. The majority of fossil bones and petrified wood are preserved in this manner.
  • Molds: These occur when the remains of the organism decays or dissolves away, leaving only an empty cavity in the rock. These can retain a surprising amount of surface detail imprinted on the rock.
  • Casts: These are when a mold becomes filled with a mineral such as pyrite, calcite, or agate, which takes the form of the mold.
  • Steinkerns: The interior of a shell becomes filled with mud, which hardens, and eventually becomes free of the matrix. Basically, a cast of the inside of a shell.
  • Trace Fossils: These are not fossils of the organism itself, but rather some trace of it -- preserved footprints in mud, for example, or nests/burrows, etc.

How to tell if it's a fossil
Does it have clearly identifiable bones/teeth/wood grain/shells? Always remember that hard parts are MUCH more common than soft part fossils. If you think you've found a tooth, you're more likely right than if you think you found a petrified eyeball.

The fossilization process has to race against decomposition. And fossil-forming can be a very long process, sometimes taking thousands of years. The harder and more rot-resistant parts of the organism are what is likely to actually be left, by the time fossilization has fully set in.

Be sure to take a look at the type of rock you found it in, and the geologic setting nearby. Is it sedimentary? Are there other types of fossils found in the area?

And if you pick it up and have to wonder, "Is this a fossil?" instead of immediately going "Wow, a fossil clam!" ....then it may not be a very good specimen anyway!

If you'd like to learn more about fossils and how to identify them, I highly recommend the following books:

National Audubon Society Field Guide to North American Fossils

Smithsonian Handbooks: Fossils

Happy hunting!

Monday, March 23, 2015

Have a location you want featured? Let me know!

Dear readers,

I've gotten a few suggestions lately about spots to cover for this blog. Do you have a location you would like to see written up here? It doesn't have to be a major spot, I'm willing to visit smaller and more out of the way sites as well.

Suggestions accepted in the comments, or you can send me an email.

I'm looking for sites located only on public land, for ease of access.

I'll take suggestions for anywhere in the whole wide world, but the chances of my actually visiting the place are vastly higher if it's in Sonoma, Lake, or Mendocino Counties, or somewhere nearish those.

Looking forward to your suggestions!