Cajon Pass

Hey there every peoples!

Alright, I have a break, so I am going to write a post I have been meaning to write for a very long time but just never got around to it. I have tried to remember as much as I could.

Way back in the early days of april me and my dad attended a second field trip with the San Bernardino County Museum. This trip took us to Cajon Pass, which sits east of Redlands in the “Inland Empire”.  Cajon Pass is a geological and paleontological laboratory, hosting a rich array of fossils and geological features. We spent all day driving around the pass visiting fossils sites and taking in some spectacular views.

The most prominent feature of the pass is the San Andreas Fault. San Andreas is the biggest fault in California and is responsible for many of our worst earthquakes. The falult runs directly across the pass, with the Pacific Plate to the west and the North American Plate to the east.

A view of the San Andreas Fault running across Cajon Pass

The presence of Pelona schist and a sag lake testify to the fault’s presence. Just so you know, a sag lake is a lake that is formed right on a fault when ground water seeps up through cracks created by movement of the fault. In the case of Cajon Pass, this type of lake is represented by Lost Lake. I guess it isn’t really lost if the curators can take people to it.

Another neat geological feature is the Mormon Rocks (or as the curators called them: “Rocks of Jesus Christ of Later Day Saints”). This is where we had lunch and a few people had a good time climbing around and exploring the rocks. Me, on the hand, stayed behind with Eric and aggravated Kathleen with our chatter about Diablo II. The Mormon Rocks were once though to be part of the Punchbowl Formation but were later found to be older than said formation. The formation was named after Devil’s Punchbowl, a geologic feature further to the east (we didn’t get to see it).

Mormon Rocks

Cajon Pass has also yielded many fossils. There are many fossil bearing layers through out the pass and because of the constant motion of the earth there, they all jumble together. Take this site for example:

A great jumble of prehistoric rocks

I cn’t remember the name of the formation on the right, but I remember it’s middle miocene in age, abround 16 to 12 million years old. And interesting thing to note is that the formation is a terrestrial deposit but at one point yielded a whale vertebra. How is that possible? Remember, this area has undergone massive remodeling thanks to tectonic boundries. What the curators think happened is that the whale was buried in an older layer at a time when the pass was underwater. The whale died and it’s vertabra was buried. Later, during the middle Miocene, the bone eroded out of it’s origonal geologic unit and was redeposited when the middle Miocene unit was being formed. So instead of a whale finding it’s way inland (like that one whale, Humphry), the vertebra was instead reworked from an older layer. Isn’t geology fascinating!

Now look at the slanted layers to the left. They are cretaceous and paleocene rocks. I don’t remember much but I remember Eric talking about a plesiosaur vertebra being found in those layers, possibly in the paleocene layers. I just can’t remember. Sorry.

Anyway, they even took us to a fossil site with fossils still in the ground! They said that those fossils have been there for 22 years. That’s because they have been left there so that they can take people to the site to see fossils in their original state. The matirx consists of sand mixed with pebbles, which seems like an unlikely place to find fossils. Indeed, the fossils were fragmentary, consisting moslty of teeth:

A fossil horse tooth in situ

Fragment of rhino tooth, possibly Aphelops

And of course, we can’t forget the curators, who braved hell and high water (and me) to take us on another fantastic trip! Can we hear a big round of applause for:

Chris Sagebiel, purveyor of geological wisdom

Eric Scot, Master of Fossil Horses and Pringle Enthusiast

Kathleen Springer, Senior Curator of Geology, Queen of Rocks, Bane of All that is Doug...

Nah, I’m just kidding. She a wonderful person to be around. But all in all, these people really make the trip. Instead of just some tour guide, we get the people who actually work out here. Thanks again for the wonderful trip guys.

Till next time!

Fossils from the Punchbowl Formation, including a horse jaw and a camel skull

3 thoughts on “Cajon Pass

  1. i found a wierd bone with a fin on it in a dry creeek in the cajon pass and was wondering if you had any idea what it could be/Users/daleroberts/Desktop/Photo 1967.jpg

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