A Way of Seeing California Biogeography

The “real” or “Californian” California can be visualized as a series of concentric rings, like ripples on a pond, beginning with the Great Valley at the center, ringed by low, dry foothills on all sides, and those surrounded, except for a few gaps, by higher, forested mountains.

The pattern is broken or more-or-less greatly modified at places around the edges where it is impinged upon by other biogeographic ripples from outside, much the way that the expanding ripples from one rock thrown into a pond get disrupted by those from other rocks dropped into different parts of the pond.

In our case, the “other rocks”, each equally large and heavy as the California rock, are:  

1. From the west, and most abrupt and huge of all outside ripples, the Pacific Ocean, making a razor-sharp demarcation all along California’s western edge, but having a considerable effect for some distance inland in terms of climate modification, even to the extent of blowing a whole suite of coast-range species clear across the Central Valley at the big San Francisco Bay wind-gap;
2. From the north, the cool, humid, forested bioregion of the Pacific Northwest, impinging on us at the northwest corner and gradually petering out southward, the last traces dying in Santa Cruz and Monterey counties;
3. From the northeast, the dry, cold sagebrush country of the Basin and Range, making a sharp line where it runs up against the high barricade of the Sierra Nevada, but seeping in through low gaps to the north, e.g. at Lake Almanor, Pit River, and west of the Modoc Plateau;
4. From the southeast, the Mojave and Colorado Desert biomes, crashing abruptly into the high southern Sierra and Transverse Ranges and coming to a sharp point in Antelope Valley, lapping over only in the most subtle, low-rainfall way into the southern San Joaquin;
5. A last ripple from a direction we don’t normally consider: UP.  High elevation and thin air make for Arctic climates (and floras) at the tops of our highest mountains, and a gradual but dramatic climatic gradation down to lower elevations; in fact this is the most pervasive “outside ripple” of all those that impinge on our little world.