CARMEL KNOLLS

Natural History

 

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Geology

The geologic history of the Carmel Valley is recorded by the rocks underfoot.  The history unfolds as we recount the events that formed each rock layer, from oldest to yongest.  

 

1) When you stop on Carmel Valley Road, ready to turn right on Route 1, the steep rock wall dead ahead is 80 million year old granodiorite (a close cousin of granite).  At that time, the Sierra Nevada were a very active volcanic province, and the granodiorite represents a cooled magma chamber that fed one of those ancient volcanoes.  It cooled 5 to 10 kilometers deep in the Earth, and somewhere around the Mojave Desert, perhaps in that topographic gap between the southern Sierras and the Coast ranges of southern California.

 

2) The granodiroite was uplifted to the surface of the Earth, while its overlying volcano was eroded away.  The granodiorite subsided in elevation to below sea level where it was then covered 50 million years ago by marine sedimentary rocks.  These marine rocks are called the Carmelo Formation; they are best exposed at Point Lobos.

 

3) About 20 million years ago, these older rocks began a northward trip to there present location, moving about 1.5 inches/year along the San Andreas Fault.  All of us are continuing that slow northwestard journey.

 

4) While the older rocks were traveling northward, they dropped to very deep ocean depths where the

Monterey Formation was deposited on them.  The Monterey Formation forms the white cliffs seen along Route One as you approach Monterey. It is also the ubiquitous ornamental rock called 
"Carmel Stone."  There is no paucity of Carmel Stone in the Knolls! And, the Monterey Formation is the main bedrock underlying our properties.

 

5) While much went on during the intervening 10 million years between the deposition of the Monterey Formation and now, there are only a three additional events of interest to the Knolls.

 

a) The seafloor where the Monterey Formation was deposited was uplifted high above sea level (it underlies Jack's Peak for example).

 

b) As it rose, it was cut into a stair-step topography by ocean waves.  The steep parts of Carmel Knolls Drive are old, weathered, sea cliffs, and the flat parts of the road are wave-cut platforms.  The topography is like a miniture version of the hills of San Francisco, or Pacific Grove, each of which were shaped by the same mechanism.  The wave-cut platforms cut into the Monterey Formation are commonly capped with a 3 to 4 foot thick layer of younger shoreline deposits.  When you dig in your yard, the hard material you soon reach is either the Monterey Formation or the nearshore deposits, that have now been well cemeted by natural calcium carbonate. 

 

c) Global sea level has risen and fallen approximately 400 ft several times in the past 2 million years.  The most recent low stand was 18,000 years ago.  At that time, most of the coastal streams cut down to an elevation about 300 ft below their present elevation.  The resulting steep canyon walls destabilized the upper valley walls, leading to a period of pervasive landslides in the valley.  Nearly the entire view in the photo at the header of this page is one of those old giant landslides.  Contact Doug Smith on the board if you would like more information about the local geology.