Caldecott Tunnel and the Orinda Formation [updated]

caldecott tunnel

Those of us in the geology community have been eager to hear more from the Caldecott Tunnel’s fourth bore project. The bore is cutting through the Berkeley Hills in a perfect transect, allowing geologists to sample every meter of the rocks along the way. This weekend, I heard some news in a presentation at the CalPaleo 2011 meeting.

The east end was where the boring began. The Orinda Formation is beautifully exposed there—most of it, anyway—on both sides of Route 24.

orinda formation

Much of it is coarse conglomerate of late Miocene age, about 10 million years old, that’s thought to represent landslides into a freshwater basin in the middle of volcanic terrain.

orinda formation

That part, naturally, has no fossils because the environment was too rugged for even large bones to survive. But there’s other stuff in the Orinda, like lava flows at the top of the unit belonging to the Moraga Formation. This is a view of the underside of the lava, where it flowed onto the moist sediments one day long ago.

moraga lava

And there’s a good amount of fine-grained sedimentary rock, suitable for preserving fossils, as you move down section toward the hills. Caltrans has a contract with PaleoResource, a well-regarded firm, to monitor the work and recover fossils that turn up. In the initial digs, the scientists found and cataloged thousands of items, including lots of fish fossils, clams and crabs, birds and the first leaf fossils ever found in the Orinda. The press tends to zero in on large mammals, though, so we’ve heard about bones from wolverines, horses, rhinos, camels, pronghorns and even the obscure oreodont.

However, PaleoResource scientists have told me that Caltrans has not allowed the paleontologists into the tunnel proper, in violation of the contract and the agency’s own policies. That’s the kind of thing that makes me awaken at night and grind my teeth. Not only are we not learning about the lower Orinda Formation, we’re not studying the transition into the underlying Claremont Formation and the Sobrante Formation on the west side.

I try to take the long view. The tunnel is being dug in three passes, and conceivably the rocks can be sampled later. But PaleoResource officials have told me their contract runs out this summer, before the next phase of digging.

So I try to take a longer view. Once upon a time, nobody cared about paleontology. Heck, they didn’t care about archaeology. Today, turning up a human bone will stop a job in its tracks. Fossils aren’t that disruptive; they can be salvaged and documented in a day or two. Many agencies and jobs go well, the paleo people and the construction people interacting well and yielding good science. Other jobs are jobs from hell, but the long arc of history is curving toward respect for science.

Update: I’ve put up some photos of new fossils from the dig on KQED Quest Science Blogs.

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2 Responses to “Caldecott Tunnel and the Orinda Formation [updated]”

  1. Naomi Schiff Says:

    Nonetheless, it might be good to lodge a complaint and see if the situation might be rectified! Presumably the paleo people are there as a condition or mitigation of the EIR and permits, and after all, it IS state law!

  2. Andrew Says:

    I’m still mulling what to do. You are correct about the law and the permits, but those are not impediments to a determined official. Meanwhile I hope to get permission to use some of the fossil photos.

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