Tuesday, February 1, 2011



The Lord raised his hands high above the American River 
and said, "Dam it.” 
And they did.
- as told by the author’s father far too many times

AESTHETICALLY, I like a lake but I don’t much care for a reservoir. Lakes are pools of water that naturally fill an impression. The level of the water doesn’t change from season to season. Lakes provide habitat for fish and amphibians. Ringed with riparian plant life, they afford shelter to birds and small mammals and provide water for the greater beasts of the field. Eventually, a lake will silt in and form a meadow as nature’s form constantly evolves. Nothin’ like a good lake for a picnic, a paddle or a skinny-dip on a moonlit night.

Reservoirs, on the other hand, are messy creations of man that while providing water for irrigation and flood protection for cities and recreation and fishing, come with dams which disrupt nature and, when water released in the summer and fall is not replenished in the winter and spring display ugly “bathtub rings” evidencing man’s disdain for the order of things. Or so I thought.

You can observe a lot of things by just watchin’.
- Peter Lawrence “Yogi” Berra

RECENTLY, FROM THE RATTLESNAKE BAR boat launching ramp – well above the reservoir’s pool – I traipsed below the bathtub ring of a depleted Folsom Lake. On display was something a little more complex simple than simple devastation.  More interesting, too.

Or is it a rock on a moonscape?
AN "ERRATIC."  Normally reserved for weathered chunks of granite left in a flat field after an ice floe melts, here's a rounded hunk of something sitting atop a plane of alluvium in an area of dry lake bottom.

Eocene Overpass
AN ARCH worn through a conglomerate with an ancient mudflow base.

A concrete example of...
CLOSE UP OF ANCIENT ROCKS from what once was a riverbed – note their water-worn rounded-to-smooth appearance – after having been overtaken by that mudflow. You remember the one: in the late Cretaceous?

THE "BATHTUB RING" viewed next to some decomposing granite. Something in granite dissolves under contact with water.

You're so vein...
A LAYER OF SOMETHING covered the metamorphic rock when it was once horizontal. Another layer of metamorphic rock piled on top. Years pass. The whole thing tilts because tectonic pressures - the origins of which are in the mid-Atlantic. Folsom Dam is constructed. The topsoil and plant life goes away. What remains is a peek at geologic history. Cool!

In looking at Peterson's "Rocks and Minerals," the vein in the above photo may be "dolomitic marble" - common to Placer County - formed through heat and pressure applied to sediments of "fairly pure carbonates." Metamorphosed (my word, not theirs) sandstone - which, I believe becomes granite - is found on either side. Originally formed undersea, close examination of the larger veins originating in this manner may show fossils that are evidenced by traces of white in the pink marble, but in a sample this thin, probably none are to be found. On the other hand, it might just be a crack filled with compacted mud from after when these rocks were inundated by Folsom Lake.

A NOT-SO-RARE MINERAL DEPOSIT (mainly bauxite) from the latter idiotic period.

A TRIP TO THE REGION below the waterline proves to be a nice look back at the past 100 million years or so – and a pleasant way to spend a mid-winter afternoon.



Plough, Frederick H., Rocks and Minerals (a Peterson Field Guide), Houghton Mifflin Company, 1988

Storer, Tracy I. and Robert L. Usinger, Sierra Nevada Natural History, University of California Press, 1963 et seq.

Van der Ven, William, Up the Lake with a Paddle (volume 1 – Sierra Foothills and Sacramento Region), Fine Edge Productions, 1998.

© 2011
Church of the Open Road Press

1 comment:

  1. Errata: "Metamorphosed (my word, not theirs) sandstone - which, I believe becomes granite - "

    The Church of the Open Road apparently enjoys the membership of no geologists.

    Actually, granite crystallizes under intense heat and pressure deep within the earth. Millions of years later, after it is exposed to wind, water, ice and sunlight, it breaks down into sand. The sand is washed down streams as sediment. It lays on the bottom of a body of water, compresses under weight and becomes sandstone. It can be pushed and bent as evidenced in the coast ranges - particularly where road builders have sliced through hill sides.

    But granite begets sandstone. Not the other way around.