Geologic map of Caldecott Tunnel area (credit: USGS ) Click here for a larger version.

If you use Highway 24 as part of your daily commute you are already familiar with the Caldecott Tunnel, which connects Orinda and Oakland — perhaps you are too familiar with the tunnel as you sit in the bottleneck traffic waiting to enter it. What you may not be familiar with, however, is the geology of the hills through which the tunnel was constructed. There are currently three separate tunnels, or bores, that make up Caldecott Tunnel. Construction for a fourth bore is now underway an is already yielding interesting geologic results. The Caldecott Fourth Bore Project website contains a wealth of information about the entire project — from funding to logistics to tunneling methods and more.

The process of excavating a tunnel produces a lot of rock and, in this case, it is sedimentary rock that is known to contain abundant fossils. The geologic map shown above depicts the distribution of distinct rock types and ages in this area. The part of the ridge that Caldecott Tunnel cuts through is made up three formations — each of which has their own color: The Orinda Formation is the orange unit at the east portal, the Claremont Chert in yellow, and an unnamed mudstone in brown at the west portal. The tectonic forces that created these hills also caused the layered sedimentary rocks to be tilted at high angles and, in many areas, the layers are standing up vertical. The rocks are older from east to west so, in this case, excavation of the tunnel from east to west is similar to drilling down into older layers.

Orinda Formation along Hwy 24 near east portal of Caldecott Tunnel (credit: Jeff Weiss, public information officer for Fourth Bore Project)

The rocks are lithified sediments that were deposited in the Miocene period, which ranged from 23 to 5 million years ago. The Orinda Formation (the orange unit by east portal in map above) is approximately 10 million years old and is known to contain abundant mammal and plant fossils in nearby areas. The Orinda Formation is characterized by a wide variety of sedimentary rocks including mudstone, sandstone, and conglomerate that were deposited in streams in creeks (see some photos of the rocks near the tunnel here.

Some mammal fossils found in the Orinda Formation include*:
•    Gomphotherium (a primitive type of elephant)
•    Hipparion, Nannipus, and Pliohippus (primitive horses)
•    Barbourofelis (member of primitive cat family)
•    Cranioceras (deer-like mammal)
•    Ticholeptus (member of extinct group of pig-like animals)
•    Desmostylus (exctinct sea cow similar to a hippopotamus)

The Miocene was the peak of mammal diversity and thought to be linked to the development of grassland ecosystems. So, next time you’re stuck in traffic leading up to the tunnel remember that you’re driving through the geologic evidence of a past Bay Area environment. Excavation of the fourth bore is really just getting started so stay tuned for more in the coming months. I will do my best to find out what I can and blog about it here for QUEST.

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* List of mammal fossils from University of California Museum of Paleontology database. If you want to learn more about specific species, you can learn a lot by simply googling the italicized names in the list above.

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Hydrogen is not exactly a fuel. That is, we don't burn it to make energy. It's used more as a medium for storing and transporting energy.

The science of hydrogen fuel cell systems is based on a simple concept. When you combine hydrogen with oxygen, energy is released. You get electricity. What makes it such a clean technology is that the byproducts of that chemical reaction are just heat and water.  So when a fuel cell takes hydrogen from a fuel tank and combines it with oxygen in the air, it produces electricity and emits only a wisp of heated water vapor from the tailpipe.

Hydrogen is combustible (remember the Hindenburg?), and needs to be handled carefully. However, there are easy ways to demonstrate electrolysis, which breaks water apart into oxygen and hydrogen, and the opposite process of joining those chemicals. In fact, you could make a type of fuel cell in your kitchen, with a popsicle stick, battery clips, Scotch tape and a few other household products. You do need one item that can't be found in your kitchen: platinum wire or platinum-coated nickel wire.

Hydrogen is the most abundant element in the universe. And hydrogen fuel cell conversion is a squeaky clean technology. But the production of hydrogen for use in fuel cells — that can produce a lot of carbon dioxide. In fact, most hydrogen is currently made by stripping, or re-forming, natural gas. That's one of the ongoing criticisms of fuel-cell technology, that it generates greenhouse gas emissions just to get the hydrogen in the first place.

Fuel cells also can store energy generated by solar-powered electrolysis, as well as similar energy generated by wind and hydropower. That's the kind of hydrogen generation that advocates hope to eventually use in fuel cells. But being able to store energy also makes it extremely attractive to harnessing wind, solar and hydropower.

For example, California could generate a lot of wind energy at night, but since electricity has to be used right away, that nighttime, offpeak energy is less valuable. But if it could be stored in a fuel cell through the electrolysis process, that would make it much more lucrative.

Listen to the Where's my Hydrogen Highway? radio report online, and watch our Web Extra Slideshow.

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