Hwy 9

Guide to the San Lorenzo Valley & Santa Cruz Mountains

A Long Time Ago

A Slightly Silly History Of The Santa Cruz Region

Sixty five million years ago, the Santa Cruz region was not in California at all. In fact it was a part of Mexico (some think it was a suburb of Acapulco). The region is perched on the edge of a massive piece of the Earth’s crust called the Pacific Plate. The edge of the Pacific Plate is sliding north against the western edge of the North American at a rate of 5.5 cm per year.

One of the most distinctive regional features is the San Andreas Fault System which is the boundary between the two gigantic plates. The San Andreas Fault is famous for the destructive earthquakes of 1906 and 1989 among others, but it should be noted that but for it, the Santa Cruz Mountains and the Monterey Bay would not exist as we know them.

The piece of the crust that the Monterey Bay region is part of is called the Salinian Block. It has a special name because it is rather mysterious and unlike other rock masses in the region (this seems appropriate somehow).

At times in the past millions of years, parts of this block have been buried several miles deep into the Earth where the fiery heat of the planet’s mantle cooked some old bay bottoms into limestone and schist and much of the rock was folded like salt water taffy.

At other times, the block has been pierced by volcanic activity leaving huge pools of magma slowly cooling into huge granite masses which would only be seen millions of years later after the softer rock surrounding them eroded away. These granite masses are closly related to the famous ones at Yosemite. In fact, they may have come from the same subterranean blob.

As the Millennia sped by, the Salinian block moved north and was variously incarnated as sea bottom, beachfront, coastal volcanic mountains, and sea cliffs. The numerous fossil beds, sandstones, mudstones, sand hills, and marine terraces bear mute testimony to the geologically long marine influence on the bay area.

Roughly 3 million years ago, the region came out of the sea for the last time to date, and the Santa Cruz mountains began to emerge between the bay and the San Andreas Fault. The mountain building process, called uplift, is related to the tectonics (plate movement) of the area and seems to be a product of the fault systems. In fact, the 1989 Loma Prieta quake raised the top of the range in elevation by 9 centimeters (6 inches). The newly lifted mountains became a barrier that the prevailing water laden winds had to climb over before continuing on their eastward path, which causes tremendous precipitation on the slopes of the mountains (2.5 meters or more in the course of a year). All this water causes a great deal of erosion, as one might expect, so that the mountains are busily being turned back into beach as they get lifted from the bay (and we are so proud of our recycling efforts!).

As the Salinian block was uplifted, the other great landscape feature of the area was formed. The Monterey Canyon is a subsea trench kilometers deep and huge in extent. It falls sharply from the coast at Moss Landing to a depth of almost 3 kilometers within a few kilometers of the beach. It winds around the bay for a total length of 80 km before ending deep in the Pacific. If this canyon were dry it would rival the Grand Canyon in size and depth.

The presence of the cold water immediately offshore greatly influences the climate and the sealife of the region. The sea canyon, the shallow waters of the bay shores and estuaries, and the coastal mountains define the region in many ways.

After the region settled into it’s current geologic profile, the Redwoods and the Douglas Firs moved down the coast and proliferated on the growing mountains. They blended with immigrants from other areas like the Knobcone Pine, Madrone, Live Oaks, and the Bay to create a climax forest that was majestic, dense, and covered most of the area. Various species of animals inhabited the region including Grizzly Bears, Banana Slugs, California Condors, and about a zillion other species of various phyla.

by Gary Starkweather
Copyright 1997-2013 iHwy, Inc.

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