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gtheo

Ammonite Localities In Sf?

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gtheo

I was wondering about the ammonite localities in SF around the Golden Gate bridge. How common are they? Are they difficult to find? Where is the best place to look? Is it worth trying to look for them or are they very rare?

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piranha

I found this paper that describes a few ammonite genera from the Pigeon Point Formation located a few miles south of San Francisco Bay.

Elder, W.P., & Saul, L.R. (1993)

Paleogeographic implications of molluscan assemblages in the Upper Cretaceous (Campanian) Pigeon Point Formation, California.

In: Dunn, G., and McDougall, K., eds., (1993)

Mesozoic Paleogeography of the Western United States-II. Pacific Section, SEPM 71:171-186

LINK

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Plantguy

Hi gtheo, they are rare in the SF bay area! Looks like Scott already gave you a lead on some things south of SF--great, much more fossiliferous than up north by SF--at least for Mesozoic stuff. When I was roaming around there finding Mesozoic macrofossil stuff in the immediate SF area was tough. That may have since changed but the Franciscan complex rocks just didnt produce much. I am aware of a couple of ammonites found a long time ago near the Golden Gate bridge...If you havent already done so look at page 9 of the Geology of the Golden Gate Headlands you'll see those documented.

http://www.nps.gov/goga/forteachers/upload/Geology%20of%20the%20Golden%20Gate%20Headlands%20Field%20Guide.pdf

We did find a few Jurrassic radiolaria in the cherts in Marin county on the north end of the bridge as that guide mentions but no macrofossils as its just not the right rock type/environment. Not sure what the access is like nowadays to that site. Alcatraz Island coughed up a few pelcypods that DL Jones with the USGS found but no ammonites that I know of--cant collect there now anyways. Only other place in the bay area that we ever found ammonites was up in Napa County in the GVsequence rocks but they were very rare as well, only 2 in 20 years of collecting---those were donated to the Napa Valley Museum up in Yountville along with the other Napa fossils we collected. Maybe a member or two who have collected more recently in SF can add additional comments for you.

Good luck hunting! I always enjoyed climbing the rocks and visiting beaches/roadcuts around that area looking for things! Regards, Chris

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Boesse

There's not much in the area for ammonites. There is an old baculite locality I unsuccessfully tried to locate along the west shore of Del Valle Reservoir - it's now underwater. There are various ammonite localities NE of the bay area, and near Taylorsville there is a late Jurassic or early Cretaceous rock unit with tons of marine inverts, including gastropods, small bivalves, and abundand Pinna; occasional ammonites are there. There might be more Cretaceous stuff up by Gualala.

Unfortunately, everything in central (and northern) CA has also been really tectonized, so none of the rocks are easy to dig through or prepare, and most of the invertebrates are warped. One of the biggest issues regarding non-coastal localities in the bay area - particularly localities in the east bay - is that many historical localities are old roadcuts which have either been built upon, or are totally overgrown with undergrowth and poison oak. In High School and early college, I tried relocating many of Stirton's and Savage's land mammal localities in the east bay, and many just don't exist anymore.

Bobby

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Rhinofly

There is an old baculite locality I unsuccessfully tried to locate along the west shore of Del Valle Reservoir - it's now underwater.

I have been researching this site...why do you think it is underwater? Doesn't the distance place it in the arroyo upstream from the lake?

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