I snapped this photo last week while visiting the Getty Museum. It shows the 405 freeway snaking northbound through the Sepulveda pass in West Los Angeles. Follow the freeway into the hills - see that thin stretch of grey wall - 8 stories of it - carved into the mountain, just past the bridge? Those are retaining walls, recently installed by CalTrans.

They're holding back Jurassic-era slate. At Zocalo Public Square, Arthur Sylvester explains:

One hundred and sixty-five million years ago, they were mud that formed an underwater seabed. At that time, stegosaurs and allosaurs roamed the Earth, although no evidence of those particular carnivorous giants has been found in the Los Angeles region. Jurassic slate is weak, crumbly, and difficult to build on.

Science is everywhere - even the dreaded 405 - if you look close enough.