Much of California is an environment that is clearly set off from its neighbors much less from the eastern part of the country. Its climate and geology is fundamentally different and it has many species of animals and plants that are found nowhere else in the world. This diary will look at the forces of nature that created such an unusual place.
One of my main sources for this Diary is
A Natural History of California
by Allan A. Schoenherr
Prior to about 15 million years ago the area that we now call California had a warm and wet climate. It also looked very different. What we now call the coast range of mountains was an archipelago of islands off the coast. What is now the central valley was an inland sea surrounded by those islands. The actual coast began where we now find the Sierra foothills. There was a mountain range in the area of the present Sierra Nevada, but the mountains were much lower than they are now.
It was a "sudden" shift in plate tectonics that transformed that world into the one we know today.
The surface of the planet is divided into a series of huge plates that are continually sliding over the inner core of hot liquid magma.
About 15 million years ago the Pacific plate began to slide beneath the North American plate in the area of present California. This occurred "rapidly" in geologic time. It caused a dramatic rise in all the land forms. The coastal islands became a coastal range of mountains. The present Channel Islands off the Southern California coast are the remainders of that process. The Central Valley became a shallow lake and the existing mountains were pushed up into the Sierra Nevada range. Yosemite Valley presents a dramatic picture of the massive uplifting of rock that occurred.
About 5 million years ago the Pacific plate shifted its push under the North American plate to the north. This resulted in the uplifting of the Cascade range that extends down Washington and Oregon and into Northern California. Mt Shasta is the most prominent Cascade peak in California.
The Cascades can be thought of as adolescent mountains in geological age. Many of them still have disruptive volcanic activity. Mt. St. Helens has provided the most resent eruption. Mt. Lassen in California is still an active volcano. It's last period of eruptions was from 1914-1917.
Changes on such a grand scale made a significant change in the climate. The much higher mountains redirected the pattern of rainfall. There is a meteorological phenomenon known as rain shadow.
The various mountain ranges catch the rainfall coming in off the Pacific Ocean. It flows down the mountains into rivers that return it to the sea. One effect of this is to create the California deserts because the rain never reaches them.
California has a Mediterranean climate. This means that the year is divided into a wet season and a dry season. Such climates occur at similar latitudes around the globe and on west facing sides of continents.
It is interesting to see that the Pacific coasts of North and South America are mirror images of each other in terms of climate. Starting in the north there is the polar arctic, then the wet temperate zone of the Gulf of Alaska, British Columbia, Washington and Oregon. Next comes California followed by the Sonora desert and then the equatorial belt of warm wet weather. Below that is the desert of Southern Peru and Northern Chile. Central Chile has a climate and geography that is very similar to California. Then comes a wet temperate belt and finally the polar region of Antarctica.
In looking at average rainfall totals down the Pacific coast of the US there is a very steady progression from wet to dry. Seattle is wetter than Portland. Portland is wetter than San Francisco and San Francisco is wetter than San Diego. When you combine this distribution with the rain shadow effect of the mountains it results in great variation in the amount of rain that falls in different areas of California.
In discussing climate people usually talk in terms of average rainfall. In California the averages are derived from years with a high degree of variability. Here is an example of annual rainfall totals for San Francisco.
Using dendrochronology or the counting of tree rings, it is possible to determine that a similar pattern of variability was in existence for centuries before weather records were maintained. Much of that variability can be accounted for by the El Nino/La Nina ocean phenomenon.
El Niño-Southern Oscillation
When Europeans arrived in California a bit over 200 years ago they found a complex ecosystem that had been only lightly touched by the Indian inhabitants. The rivers cutting through the mountains deposited rich topsoil in the valleys and nourished a rich diversity of life. Plants and animals had evolved specific adaptations for dealing with the peculiarities of the climate. Of particular interest to the issue of water resources are the various species of fish that migrate from fresh water to the ocean and back to fresh water in their life cycle.
This is a brief overview of the climate and environmental legacy that is California. Next we will look at how this legacy has been transformed by the effort to develop, manage and exploit it.
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