My interest in the natural world has followed an odd sequence.At…
My interest in the natural world has followed an odd sequence.
At first I was drawn to birds. Then it was the insects the birds were eating, and then the plants depended on by the insects.
Now it’s rocks.
Phase II of the Franklin Trail behind Carpinteria is now open, and today Linda and I took Rory on a hike to check it out. There was lots of cool stuff to see; a higher vantage point to view the valley, trees with colorful poison oak beneath them, a big sycamore with bear claw marks leading up its trunk.
But the most interesting thing for me was the geology along the trail. The large image above shows (I think) the transition between the Sespe Formation (on the left), with reddish sandstone and conglomerate, and the Coldwater Formation’s yellow sandstone on the right.
The boundary dates to about 40 million years ago. The Coldwater sandstone is older, the Sespe conglomerate younger. The layers were laid down in the vicinity of present-day San Diego; since then a big chunk of land has rotated clockwise, bringing the rocks to their present location in south Santa Barbara County. In the last 2.5 million years they’ve been tilted up, such that what originally were horizontal layers are now angled up at a 60-degree angle.
The Coldwater sandstone was laid down at the bottom of a shallow coastal sea. Toward the end of that process, as the world’s climate transitioned from being very much warmer than today to being as cool or cooler than today, sea levels fell dramatically, and the rocks in that photo went from being underwater to being part of a low-lying coastal plain. Wave action in the surf zone (maybe?) or periodic river flooding produced the rounded pebbles embedded in the reddish Sespe conglomerate.
It’s cool to be able to read that history in the rocks. I’m just a baby at geology, but I’m looking forward to learning more.
Reposted from http://ift.tt/1FRZ7kV.
Tags: geology, carpinteria, coldwater formation, sespe formation.
