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Low Tide at Pescadero Beach, California

Collecting Agates and Other Rocks

By Kevin Anderson, member SFGMS

On Sunday, Feb. 8th, a group of about 15 SFGMS members and friends met in the parking lot at Pescadero State Beach, about 40 miles south of San Francisco. The occasion was a seasonal low low tide (or nearly so), promising a splendid opportunity for collecting beach agates. Rain threatened early on but was stayed, and the sun came out for most of the afternoon - very helpful as the bright light makes those agates just glow in the surf. All present were well rewarded with agates, jasper, carnelian, petrified whale bone and many other interesting beach rocks.

To get to the beach you follow the trail out a rock spit off the South end of the parking area to a gap, where you can climb down. It's probably about 20 feet down to the large rocks below the cliff, then another 10 - 15 feet of slope to the surf at high tide. This picture is looking Northwest from the parking lot above the collecting area, which is below and left. The adjacent beach area North of the trail is Pescadero State Beach - where collecting is highly frowned upon. There's more sand and less agate - so we didn't go there anyway.


(photo by Dave Bier)

The collecting area when the tide is in is very rocky, strewn with boulders which can be difficult to navigate. As the tide recedes sandy patches begin to appear, which helps a bunch for getting around.


(photo by Hadassah Fliescher)

There's a fair slope to the beach and at the lowest tides the finer rocks and agates are wonderfully exposed. This picture is from the South, looking North across the beach to the rock spit, and the gap in the cliff. The tide is out... you can see the high tide line above the rocks at the base of the cliff, and in the distance beyond the spit, the powerful waves that constantly churn this beach to make and deposit so many interesting stones. The trail seen in the first picture above runs along the top of the cliff - the parking area is to the right of the picture. Getting down (and back up) is not really as difficult as it may look from here - just take your time.


(photo by Hadassah Fliescher)

If you see a group of people walking around with their heads down, they could be in mourning or depressed, but they might just be very happy rock hounds! If you're willing to get your feet wet, the edge of the surf at low tide yields an abundant bounty, but there were great finds all over the beach, right on up to the cliff base!


(photo by Dave Bier)

This picture is looking South down the San Mateo coast at the end of the day as the tide and the inclement weather begin to come back in. Besides rocks, there are numerous interesting tide pools to study and a great variety of migrating birds passing through.


(photo by Hadassah Fliescher)

So, what did we find? Plenty! As stated above, amongst the group, we found agate, jasper, carnelian, petrified whale bone and many other interesting beach rocks yet to be identified. Below are some of the rocks I collected - I think I brought home about 20 or 30 lbs. Of course, picked up the heavy pieces early and carried them around all afternoon. I made the remaining images by scanning the rocks on my flatbed scanner... an excellent technique used by author and fellow beach-collector Josie Islin, who has produced four very fine books using this method. She spoke at a recent monthly club meeting and let us in on the technique, which is quite easy to do and well worth experimentation.

First, a couple of non-agates: This is just a beach rock, but with a pleasing 6-ray star pattern - probably quartz veins. It's about 2-inches across.

This chunk of rock is about 7 inches tall and covered in ocean-swept calcite crystals. It looked like a cliff face with spring borne waterfalls running out of it, so I stuck all 5 or 6 lbs of it in my vest pocket and carried it around with me all day.

A good sized chunk of quartz... (I guess it looks like citrine) about 5-inches top to bottom - a couple of pounds at least. It's kind of translucent with definite crystal structure, I'll have to decide what I'm going to do with it - cut it or leave it alone... the ocean has tumbled it quite nicely - it just feels good to hold it in my hand.

The smallest agate in this picture is 2 inches across. It's covered with very fine banding and would probably polish up to show it very distinctly... or I could cut it open to see what's inside. The two larger agates look like cutters to me.

Here's a larger view of the smaller of the three stones above, showing the banding.

And here's a very sweet little one-inch long agate with delicate banding... Looks like it's trying to tell me something.

...and a group photo of the smaller agates I collected. These range in size from about 1/4 inch to 1-1/2 inches. I could have collected maybe 5-10 times this amount if I was more aggressive, which I became only after finally losing in my effort to keep out of the surf. Once it didn't matter, since I was already soaked, it was fairly easy pickings. Fortunately I had the good sense to bring dry pants, shoes and socks to change into at the end of the day. The banded agate just above the lower right-hand corner is the stone shown in the picture above.


These were not the only rocks I brought home. Among the others, I have a baseball sized hunk of what looks to be a jasper of some kind, or maybe jasp-agate - I'll cut it open to, hopefully, find out what it is, a perfect granite "goose egg" - and numerous interesting but yet-to-be identified goodies.

It was truly an excellent day. It started out looking like rain, but by the time we got on the beach, blue sky and a warming sun won out. The fine weather lasted until we were just getting off the beach, maybe an hour before sunset.

In response to a desire to organize more field trips closer to home, so more members can participate, this trip was a great success. Everyone was very pleased and we'll be watching the tide tables anticipating a return trip to this great location. If you'd like to join us on a day trip, join the club - it's is easy, affordable and fulfilling. (Click here for membership information). Members, keep your eyes opened for announcements here on the website, in the Mineralog and on the bulletin board at the club house for news about all upcoming field trips.

Oh, here's one last agate...

Have a nice day!

The San Francisco Gem & Mineral Society, Inc.

4134 Judah Street

San Francisco, CA 94122

415-564-4230

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on the first Friday of each month, 8 p.m. at the clubhouse.

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